F770
Skin Disease

bacterial | fungal | parasitic | allergic | autoimmune | neoplastic | endocrine-related | miscellaneous

Introduction: Skin problems in dogs are among the top reasons for a visit to a veterinary clinic. This discussion will review many of the most common skin problems seen in dogs. The information will be divided into infectious, allergic and autoimmune (immune-system related), neoplastic (cancerous), endocrine (skin problems caused by problems with the organs that excrete hormones and related substances), and miscellaneous skin diseases (scaly skin, pigment abnormalities, nutritional skin diseases, etc.).

Introduction: Bacterial skin infections are commonly grouped under the term "pyoderma," meaning a skin disease that causes pus. Pyoderma is further broken down into more specific categories. The bacteria most often responsible for pyoderma is Staphylococcus intermedius. There is almost always an underlying reason for the presence of a bacterial skin infection in dogs; however, this underlying primary cause is not always found.

Introduction: There are several types of fungi which can infect the skin of dogs. Most fungal skin infections can appear identical to other types of infections (bacterial pyoderma and demodectic mange). Therefore, specific diagnostic testing should always be performed on a suspected fungal skin infection to ensure an accurate diagnosis and treatment.

Causative Agents: There are at least 20 different species of dermatophytes which have been found to cause skin infections in dogs; however, the vast majority of cases are infected with one of two species: Microsporum canis and Trichophyton mentagrophytes.

Clinical Signs: Dermatophytosis in the dog appears very similar to other infections of the skin. It is practically impossible to tell the difference between dermatophytosis, demodectic mange, and some types of bacterial pyoderma. Generally these fungal infections appear as areas of hair loss, with flaky, crusty, irritated skin. These areas usually cause some degree of discomfort to the dog.

Transmission: Dogs can get ringworm in several ways. They can get the fungi directly from other animals, including rodents, cats, dogs, and humans, or from the soil. They can also be exposed to fungi found on surfaces, such as brushes, blankets, and bedding.

Diagnosis: A dermatophytosis infection is diagnosed by performing a culture of the hair from an affected individual. This is accomplished by taking hair samples from the outside edge of a few of the lesions. The hair is then placed on fungal specific media and any dermatophytes are allowed to grow. Most culture results can be performed and interpreted by a veterinarian. Results may take up to 10-14 days to provide an accurate answer. Other techniques commonly used include a Wood’s lamp test and direct microscopic examination of hair and scales of affected animals. Wood’s lamp testing involves close examination of the skin of the animal with a special light which causes the hair and skin to fluoresce a bright apple-green color if the pet is infected with a dermatophyte. Wood’s lamp testing is only accurate in about 50% of cases. Direct microscopic examination with the aid of potassium hydroxide preparations is also done. This procedure, however, is time consuming and a positive diagnosis may be made in only 50-60% of cases.

Treatment: There is a large variety of medications and treatment options available for dermatophytosis therapy. Most often, a combination of several types of therapy is utilized for maximum results.

1. Affected areas should be clipped; cases with widespread lesions should receive whole-body clips. This may worsen the problem initially.
2. Whole-body topical therapy should be used in all cases. Shampoos (chlorhexidine, miconazole, or iodine based) and dips (lime sulfur, sodium hypochlorite, and chlorhexidine based) are types of effective whole-body topical therapy which can be used.
3. Systemic therapy (treatments going to the entire body) should be used in many cases. Systemic treatments include griseofulvicin, itraconazole, and ketoconazole. Because griseofulvin is teratogenic (causes severe birth defects), it should NEVER be used in pregnant animals and must be used with great caution in breeding females. Systemic anti-fungals are usually very expensive especially for larger dogs.

Prevention and Public Health Concerns: Dermatophytosis is "zoonotic," which means that the disease is contagious to people. Care should be taken when a pet is diagnosed with dermatophytosis. Follow the veterinarian’s instructions when treating ringworm. Keep the dog’s skin healthy. Because certain conditions encourage fungal growth, do not allow the dog’s skin to remain damp and dirty. If ringworm is identified on the dog, all bedding, combs, brushes, and cages must be thoroughly cleaned and disinfected. A 1:10 dilution of household bleach can be used. The fungal spores remain viable for up to 18 months in the environment. Frequent washing of hands, bedding, and clothing which comes into contact with the affected animal is very important. A thorough vacuuming of carpets, vents, and rugs is also essential. Steam cleaning carpets may also help. A physician should be contacted if people in the household become affected with skin abnormalities.

* For additional information on ringworm infections in humans, refer to page F998.

2. Sporotrichosis:

Causative Agent: Sporothrix schenckii is a fungus which causes skin infections in dogs worldwide on a sporadic basis. In dogs, sporotrichosis is usually associated with a puncture wound caused by a splinter of wood or thorn. This disease tends to affect hunting dogs and other dogs which spend time outdoors in contact with trees, bushes, and shrubbery.

Clinical Signs: Affected animals have multiple nodules of infection in the skin and tissues underlying the skin. These nodules may be ulcerated and crusted, and may have a draining discharge. If a limb is affected, the infection may spread upward toward the body and may cause inflammation and infection to occur in the lymphatic vessels and lymph nodes which are closest to the affected limb. Secondary bacterial infections can occur.

Diagnosis: Diagnosing this disease can be challenging in dogs. At body temperature, Sporothrix schenckii lives as a yeast form that can be seen on cytology when present. The challenge in dogs, however, is that relatively few yeasts are present in the nodules, and they can be difficult to find. If cytology is unhelpful in yielding a diagnosis of sporotrichosis, other diagnostic testing is available. Fungal culture is probably the most commonly successful diagnostic tool in the diagnosis of sporotrichosis; results may take several days to a couple of weeks before they are available. Submission of a sample of tissue for histopathology is another method of diagnosis; however, it may be difficult to find the fungal organisms present in the sample. When all other attempts at diagnosis have failed, immunofluorescence staining of discharge or tissue may be performed by the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.

Treatment: Treatment of Sporothrix schenckii infections may be accomplished with the use of a supersaturated solution of potassium iodide (SSKI). This solution should be given orally and then continued for at least one month after the nodules completely subside. Recurrence of infection is common when treatment has not been administered for a long enough period of time. Side effects of SSKI include vomiting, lethargy, weakness, and nasal discharge. If side effects are severe, alternative therapy may be offered. Such therapy includes ketoconazole or itraconazole, both of which are general antifungal drugs. Antibiotics for secondary bacterial infections should always be a part of therapeutic plans for sporotrichosis.

Parasitic Skin Infections: When we speak of the various parasites which infect the skin of either people or animals, they are specifically referred to as "ectoparasites," meaning parasites which remain on the surface. In contrast, "endoparasites" are those parasitic organisms whose life cycles favor the internal environment of the body. The following are some of the most common ectoparasites found in pets.

Introduction: Ticks are a common bloodsucking ectoparasite which cause skin disease in dogs. There are many different species of ticks that can be found throughout the world. The most important health problem associated with ticks is not the skin disease they cause, it is the disease they might transmit. Ticks are responsible for transmitting a large number of microbial diseases to dogs and other species, including man. Some of the diseases ticks are responsible for transmitting may be life-threatening to dogs and people. Babesiosis (piroplasmosis), Lyme disease, ehrlichioisis (tropical canine pancytopenia), Rocky Mountain spotted fever, tularemia, Q fever, and Colorado tick fever are all infectious diseases which are transmitted by ticks.

Clinical Signs: Ticks may attach themselves to any part of a dog and often cause a local inflammatory reaction in the skin at the site of attachment. Toxicosis (tick paralysis) and severe blood loss in massive tick infestations also occur.

Diagnosis: When attached to an external location on the dog, the cause of the problem is usually readily identified, because the tick is quite large when engorged with blood. Sometimes, the tick may attach itself in a more difficult area to access, such as inside the ear canal. This can make diagnosing this problem more complicated.

Treatment: Once the problem is identified as an attached tick, removal must be performed. Because mouthparts have usually not become embedded in the skin, removal is usually quite easy if done within the first hours after attachment. Cautiously removing each individual tick with thumb forceps is acceptable for some species of tick; however, other species secrete a type of cement which may make complete removal much more difficult. Leaving mouthparts embedded in the skin may cause irritation and secondary bacterial infections. If the tick cannot be safely removed, there are many different products that are very safe and effective at treating tick infestations. These products are listed below under prevention.

Prevention: Treatment for the various microbial diseases ticks can transmit is often complicated and costly. Because of this, prevention of tick infestations is of great importance. A variety of quality products exist which may be administered before a dog is taken into an area known to harbor ticks. Over the counter products which may be helpful include collars, sprays, dips, powders, and shampoos. Insecticidal flea/tick collars are generally more effective than ultrasonic collar devices. Sprays usually have rapid action, but may be difficult to apply in a thorough and consistent manner. Dips are generally rapid-acting and long-lasting and may be given through a pet grooming facility or at home. Tick powders are effective but messy and usually vary on how long they will last. Shampoos are usually good for rapid killing of ticks, but some have no residual (lasting) benefits. Prescription products are generally extremely effective, long-lasting, and safe. Pour-on (drip-on) formulations that are available include Frontline, Kiltix, and Revolution. The Preventic Tick Collar, available through veterinary clinics and hospitals, claims to be the only flea and tick collar that detaches and kills ticks effectively.

* For additional information on tick borne diseases see page F998.

Introduction and Causative Agents: Generalized mite infections in dogs are usually grouped under the common disease term of "mange." Mange is then more specifically broken down based on the species of mite which is responsible for the infection. In dogs, the three types of mange most commonly encountered are demodectic mange (caused by Demodex canis), sarcoptic mange (caused by Sarcoptes scabiei), and "walking dandruff" (caused by Cheyletiella yasguri). A fourth type of mite which infects dogs is Otodectes cynotis, causing a local infection in the ear canal and surrounding skin.

1. Demodectic mange (demodecosis):

• Introduction: This type of mange can be a particularly difficult disease to manage. Demodex canis is found in the skin in small numbers of most normal dogs. Pups acquire Demodex mites from their mothers when nursing. Animals which develop demodectic mange are thought to have a deficient immune system which allows larger than normal numbers of mites to grow.
  
  
• Clinical Signs: Signs usually include hair loss, crusting, and mild to intense itching. The region around the eyes, mouth, and feet are frequently affected; however, the infection may occur on any area of the body. Localized or focal demodecosis is a minor type of mite infection. These focal infections can be found as small areas or patches of hair loss, flaky skin, and inflammation. They can appear as one or multiple lesions.

Generalized (whole-body) infections can (and frequently do) affect the entire body of the dog and may affect puppies or adults. In these infections, the skin becomes coarse, dry, and red (these infections are sometimes referred to as "red mange"). Puppies that are affected with whole-body Demodex canis infections are quite often purebred and have an inherited defect of the immune system which allows growth of the mites. Adults that are affected with whole-body Demodex canis infections usually have an underlying illness which causes suppression and weakening of the animal’s immune system allowing growth of the mites. Such diseases may include hypothyroidism, Cushing’s disease, diabetes mellitus, or cancer. Secondary bacterial infections of the skin are very common with generalized demodectic mange. In extremely severe cases, the secondary bacterial infections can spread to the bloodstream (septicemia) and may lead to death of the animal.

• Diagnosis: Diagnosing demodectic mange is accomplished by first taking deep scrapings of the skin. When taking a skin scraping looking for demodectic mange, it is important to get a small amount of blood with the sample. The reason for this is that the mites live deep in the hair follicles. If small capillaries of blood are reached/ruptured with the scraping, the scraping is deep enough to include these mites in the sample. The mites themselves are then identified microscopically, making the diagnosis relatively simple.
  
  
• Treatment: Except for the focal form, treatment of demodectic mange is complicated and often difficult. Because it can resolve on its own, therapy is often not necessary for the focal form. Topical products like benzoyl peroxide gel or benzoyl benzoate ointment (Goodwinol ointment) can be used if treatment is required in these focal infections. Antibiotics may be used if secondary bacterial infection occurs.

Treatment of the generalized forms is always necessary. Steroid therapy for itching is unacceptable because it almost always makes the infection worse by further weakening the immune system. Adults with generalized infections should have the underlying problem addressed and properly managed to help strengthen the immune system. Affected females should be spayed as soon as possible, because estrogen (a steroid type hormone) can also weaken the immune system and should be eliminated. Affected puppies usually carry an inheritable defect in the immune system; these puppies should be neutered or spayed to prevent passing on the defect.

Amitraz (Miteban) dips are the only FDA-approved specific treatment for demodectic mange in dogs. Amitraz dips should be performed every week in severe cases and every 2 weeks in mild to moderate cases. Skin scrapings should be performed every 3 weeks to assess the effectiveness of amitraz therapy. Dips should continue for 4 weeks after scrapings are negative for any mites. Other drugs that can be used include ivermectin (doses used are fatal to Collies and Shetland sheepdogs!) and milbemycin oxime (Interceptor). Ivermectin is now considered the treatment of choice in dogs which have failed to respond to amitraz. Finally, antibiotics are frequently utilized to fight secondary bacterial infections.

• Prognosis: The focal form carries the best prognosis for full recovery, followed by the adult generalized infections which may be curable if the underlying disease process can be resolved or managed. The puppy (juvenile) generalized type of infection is the least favorable, with most requiring very aggressive treatment for management of the disease and few ever achieving full recovery.

2. Sarcoptic mange:

• Introduction and Causative Agent: Sarcoptes scabiei mites have a preference for a certain species of host. For example, some types of Sarcoptes scabiei prefer humans, while others prefer dogs or pigs. While a mite infection can spread from one species to another (i.e. from a dog to a person), the resulting infection is usually mild and goes away on its own. When an infection occurs in the species of preference, however, the resulting skin problems can be extremely severe.
  
  
• Clinical Signs: Sarcoptic mange in dogs usually takes 1-2 weeks from exposure before clinical signs begin. Itching usually intensifies over the next couple of weeks and may become one of the most agonizing skin conditions to affect dogs. The mites seem to prefer hairless areas on the body such as elbows, hocks, chest, abdomen, and tips of the ears. This mite causes a reddened, crusting appearance to the skin. Secondary bacterial infections of the skin are common. Some dogs can have significant inflammation and itching with relatively few mites. This supports the idea of a hypersensitivity reaction similar to fleabite hypersensitivity (see above). Sometimes sarcoptic mange can occur without the typical crusting and reddening of hairless areas on the body; usually these dogs have intense itching, but no other clinical signs. These cases are referred to as "sarcoptes incognito," and may be more difficult to diagnose.
  
  
• Diagnosis: Diagnosing sarcoptic mange may be more difficult than demodectic mange, but it is usually easier to manage. Multiple skin scrapings are usually performed; if mites or mite eggs are seen, a diagnosis is established. Fecal flotations may also be helpful in identifying mites and eggs that may be ingested while a dog is grooming itself. However, mites and/or eggs are seen in only 20-50% of affected dogs. In challenging cases, specific mite treatment products are often administered and the animal observed to see how it responds to the treatment. If the pet responds favorably to the treatment, a diagnosis of sarcoptic mange infestation can be made.
  
  
• Treatment: Treatment of sarcoptic mange is usually very successful. Weekly lime sulfur or amitraz (Miteban) dips can be very helpful; usually treatment for 4-6 weeks is sufficient for resolution. Ivermectin is a very effective drug which may be used either orally or as a series of subcutaneous injections; however, it is important to remember that this drug is fatal to some breeds of dog at the doses needed to treat sarcoptic mange. Herding breeds such as Collies, Shetland sheepdogs, Old English sheepdogs, and Australian shepherds may have very severe reactions to ivermectin and should be treated with an alternate therapy. Milbemycin oxime (Interceptor) and selamectin (Revolution) have been used successfully for cases of sarcoptic mange and may be used in those breeds sensitive to ivermectin. Interceptor is given orally while Revolution is a pour-on type treatment. Most cases appear to respond to a single treatment of Revolution. Treatment of all animals in contact with the affected individual is of great importance for complete control and resolution of sarcoptic mange regardless of the type of therapy used.

3. Cheyletiella yasguri:

1. Atopic or Allergic Inhalant Dermatitis:
   Introduction: The term allergic inhalant dermatitis implies that the dog inhales the substances which then lead to a reaction in the skin. Atopic dermatitis is a less restrictive term, implying that the allergic reaction is a response to ordinary environmental substances. Many studies indicate that atopic dermatitis may result from not only inhalation of these ordinary substances, but also through ingesting these substances or when these substances directly contact the skin. Because of this new understanding, the term allergic inhalant dermatitis is falling out of favor. Atopy is a general term used to describe these types of allergic reactions.
   
   Atopy is often considered an inherited problem passed on through genetics. Certain dog breeds to tend to develop atopic dermatitis more frequently than others. West Highland white terriers, English setters, Cairn terriers, Wheaten terriers, and Fox terriers are probably the five most allergic dog breeds. Other breeds which are frequently diagnosed with allergic skin disease include Labrador retrievers, cocker spaniels, and Chinese shar peis. Dogs with atopy usually begin to experience skin problems somewhere between the ages of 1 and 7 years.
   
   Causative Agents: Dogs can be allergic to a variety of things including regional pollens, house dust, house mites, air-borne molds, human dander, and often food proteins to name a few. All of these are considered allergens or substances that produce an allergic reaction. When one of these substances contacts the animal, the immune system produces several types of antibodies known as immunoglobulins. Most of these have the absolutely crucial function of fighting infection. One specific type of antibody, known as Immunoglobulin E (IgE) plays a significant role in allergic reactions. Basically, the immune system of dogs with atopy over reacts and a hypersensitivity reaction results. This hypersensitivity reaction produces excess IgE and causes the release of histamine and other substances. IgE is generally found in very high levels in dogs which suffer from atopy.
   
   Clinical Signs: The signs of atopy include mild to severe itchiness (pruritus) and skin redness. Hair loss (alopecia) and thickening of the skin are also possible. Secondary bacterial or yeast infections are common and may result in drainage of pus, crusting, and further itching. Areas of a dog which are most frequently affected by atopy include the feet, face, ears, axillary (armpit) areas, and inguinal (groin) areas. Atopy may or may not be seasonal, depending upon the offending substance causing the reaction and the individual animal. Reactions to pollens tend to be worse in the late summer, whereas reactions to house dust may be worse in the winter when windows are left closed and furnaces are turned on, blowing dust from air vents. In many dogs, the seasonal nature of atopy may steadily progress to a constant problem, with no relief as the seasons change.
   
   Diagnosis: The diagnosis of atopy is somewhat of a challenge. In many situations, no formal testing is done, and the diagnosis is made based on history, clinical signs, and response to treatment. Testing is available, however, and can be extremely beneficial for dogs suffering from atopy.
   
   The intradermal skin test is generally accepted as the best test available for the diagnosis of atopy. To perform this test, an experienced veterinarian (usually a veterinary dermatologist) injects small blebs of reagents/allergens to which dogs are known to react directly into the skin. Allergic dogs will react by forming a lump or "wheal" in the area associated with the specific injection(s) they are allergic to. Sedation is generally very helpful when performing the test and helps to decrease interference with natural steroid release from an excited or anxious animal. The pet undergoing an intradermal skin test should not be treated with any corticosteroids (i.e. prednisone) for at least 6 weeks prior to testing. The steroid can prevent the skin from reacting to the offending reagent(s). This test is very dependent upon the experience of the professional performing the procedure and the interpretation of the results.
   
   The second type of testing commonly used in the diagnosis of atopy is serologic allergy testing. Currently, three major types of serology tests are available which can be used for diagnosing atopy: ELISA (enzyme-linked immunosorbent assay), RAST (radioallergosorbent test), and liquid-phase immunoenzymatic assay (VARL). Blood from a suspect atopic dog is sent to a laboratory for measurement of IgE levels against specific allergens. A detailed history of the condition and the region of the country where the dog resides are also included. Testing is performed on the blood using a variety of allergens (regional pollens, house dust, house mites, air-borne molds, human dander, and often food proteins) to which the dog may be reacting. These tests measure IgE levels in the animal’s blood and report any allergens where there is a high IgE response.
   
   As a side note, a smaller and much quicker ELISA test, called the Allercept E-Screen IgE test, is currently available through Heska Laboratories. This test (which can be run in a veterinary clinic in 5 minutes) shows the total IgE levels in a dog’s blood sample and may indicate what animals require more extensive and specific testing.
   
   Histopathology of a biopsy sample from affected skin may be used as an aid to help in the diagnosis of atopy, but generally cannot provide a specific diagnosis of atopy.
   
   Treatment: Treating atopy is another area of challenge. Treatment is broken into 2 major categories: immunotherapy and non-immunotherapy.
   
   1. Immunotherapy, also known as hyposensitization, consists of desensitizing the dog’s immune system to the allergen or allergens which cause the allergic reaction. In order to offer this type of therapy, either intradermal skin testing or serologic allergy testing must be performed in order to specify the exact offending allergens to be desensitized against. The way hyposensitization works is extremely complex. Small, measured amounts of the specific allergen(s) to be desensitized against are injected regularly under the skin. These injections may be administered at home or in a veterinary hospital. A specific schedule with the frequency and amount of each injection is outlined and strictly followed. Studies show that between 50% and 80% of treated animals have a good to excellent response. Immunotherapy has been described as the mainstay of atopy treatment in dogs; however, in reality it is underutilized as a therapeutic tool. This is probably due to both the cost involved in the testing and the immunotherapy itself. Further research needs to be done in the area of canine immunotherapy to help better understand all the factors which affect the success of treatment. This will help the veterinarian select the best candidates for a successful response to this type of therapy.
      
      
   2. Non-immunotherapy is a collection of medications used in the treatment of atopy and other types of allergies. Each category will be briefly discussed here under the heading of atopy, but it should be remembered that all types of allergies may respond to one or a combination of the medication types listed.
      
      
      1. Corticosteroids: Corticosteroids are a class of powerful anti-inflammatory drugs, which are commonly used in the control of canine atopy. Corticosteroids given systemically (orally or by injection) are necessary to help control atopy in a large number of cases, although they are usually less effective in helping to control food allergies in dogs.
         
         Prednisone, prednisolone, methylprednisolone, triamcinolone, and sometimes dexamethasone are often used in dogs. Corticosteroids are generally inexpensive, but have undesirable side effects. These side effects include the excessive need to drink water and urinate, appetite changes, behavior or personality changes, and liver irritation. Because of these side effects, the main goal with corticosteroid therapy is to control the condition adequately on the lowest possible drug dose. Usually, the right dose given orally, every other day is both effective and minimizes undesirable side effects. Many of the following medications may be used with the attempt to reduce the need for corticosteroids.
         
         
      2. Antihistamines: Antihistamines are a class of anti-itch therapy drugs used commonly in people with allergies. Antihistamines are only beneficial in about 20-30% of dogs with atopy or other types of allergies. There are several antihistamines available, and it is generally very difficult to predict which, if any, will be effective in any given dog. Antihistamines may be synergistic (more effective if given together than separately) with essential fatty acids. Some available antihistamines which may be utilized in the treatment of allergic skin problems include diphenhydramine (Benadryl), hydroxyzine, chlorpheniramine (Chlor-Trimetron), cyproheptadine, and clemastine (Contac). It has been suggested that a first attempt at treating a dog with atopy (if non-immunotherapy is to be pursued) begins with essential fatty acid treatment and then multiple two week trials of several different antihistamines. If a combination is found to be beneficial to the dog, this therapy may be used either exclusively or in combination with other medication based on need. If no antihistamine is found to be effective, corticosteroids are then used.
         
         
      3. Essential fatty acids: Essential fatty acids (EFA) are composed of Omega 3 and 6 fatty acids, with the most emphasis on the Omega 3 fatty acids to best control itching in dogs. EFAs are effective in 10-20% of patients and should be given for at least 3 months to observe maximal benefit. Some diets supplemented with Omega 3 fatty acids have shown promise in helping to reduce itching in dogs with atopy. EFAs are considered to be very safe, with adverse side effects occurring only very rarely. EFAs are generally given daily as a capsule or liquid.
         
         
      4. Tricyclic antidepressants: There is a significant psychological component to many allergic skin problems. This class of drugs works by helping to minimize self-destructive behavior such as licking, chewing, scratching, and biting.
         
         Tricyclic antidepressants may also work more directly at reducing the amount of pruritus (itching) experienced by dogs suffering from allergies. Side effects of these medications can include drowsiness, heart rhythm disturbance problems, and seizures (rarely). Some of the specific drugs which can be used include amitriptyline, clomipramine, doxepin, and fluoxetine (Prozac). Certain medications have undesirable interactions with tricyclic antidepressants and should be avoided when treating with this class of drugs. In general, these drugs produce positive responses in about 20-25% of cases.
         
         
      5. Topical therapy: A large number of topical medications exists that can be helpful in cases of atopy. Most of these products, however, must be used along with other therapy and not as the sole treatment for allergies. By far the easiest and most cost-effective is cool-water bathing, which may give relief for up to 1-2 days. Other types of topical therapy include shampoos/conditioners, lotions, and sprays. Shampoos which reduce pruritus (itching) may contain oatmeal (see page G207), local anesthetics such as pramoxine, antihistamines such as diphenhydramine, and corticosteroids such as hydrocortisone. Cooling agents such as camphor and menthol may also be helpful in replacing the itch with a cool sensation. Dry skin increases the sensation of itching and may be alleviated with skin moisturizing lotions, shampoos, or emollients such as fatty acids, glycerin, and oatmeal. Sprays may contain antihistamines, corticosteroids, or local anesthetics. Daily foot soaks with shampoos are particularly effective in dogs which suffer primarily from itchy paws, while sprays may be most effective for use in small problem areas.
         
         
      6. Dietary therapy: Dietary therapy is generally beneficial to those animals suffering specifically from food related allergies (discussed below); however, exceptions do exist. Among these exceptions are diets containing essential fatty acid supplements (discussed above). For animals that suffer from food allergies, dietary therapy is the primary treatment. A variety of "low allergy" or hypoallergenic diets exist. Many of these diets may be purchased as over the counter diets, while others are sold only as prescriptions through veterinary hospitals and clinics. Many of the diets available only by prescription through veterinarians are used in the most severe cases. Cases that use the prescription diets tend to have a greater success rate than those that use only the over the counter diets. There are so many types of diets which may be used in food allergies that no attempt will be made here to list them; see the section on food allergies for more information on the properties of these hypoallergenic diets.
         
         
2. Food Allergies:
   Introduction/Causative Agents: Allergic skin disease resulting from an adverse reaction to food is responsible for up to 15% of all skin related allergies in dogs. Food allergies along with food intolerances make up a broader category known as food sensitivities. Food allergies are due to a reaction by the body’s immune system to certain substances (allergens) in food. Food intolerances do not involve the immune system and are usually due to certain types of food such as dairy products. It generally takes some time for a dog to develop an allergy to food, and some dogs may eat the same diet for years before they begin to react to an ingredient. Allergens which are most commonly associated with food allergies include beef, milk, soybean, chicken, pork, yeast, corn, and wheat. There are no strong breed predilections for food allergies in dogs, although according to some dermatologists, the retriever and terrier breeds are probably the most commonly affected. Dogs first diagnosed with food allergies tend to be younger, and more than 80% are affected at less than 3 years of age.
   
   Clinical Signs: The signs of food allergy in dogs are similar to atopy. They include moderate to severe itchiness of the skin in the feet, face, ears, axillary (armpit), and inguinal (groin) areas. Up to 20% of dogs with food allergies may suffer from persistent and/or recurrent inflammation and infection of the ears only, with no other body areas affected. Only rarely do vomiting or diarrhea accompany skin problems in dogs with food allergies. Like atopy, secondary bacterial or yeast infections are common. Food allergies are not seasonal.
   
   Diagnosis: The diagnosis of food allergy is accomplished with a dietary trial. During the trial, a diet with a limited number of possible food allergens is fed for 6-8 weeks. Throughout the trial, additional food and food products (table scraps, snacks, chew toys, or palatable medications) must be eliminated. The diet itself can be either home-made or commercial, but must contain only carbohydrates as a base and one protein type to which the dog has never or only rarely been exposed. Such protein sources can include lamb, fish, duck, or venison. The carbohydrate base is usually composed of cooked rice or potato and is the main source of calories during the trial. Homemade diets are usually the best. Commercial hypoallergenic diets such as Lamb & Rice can be used and are generally successful in 75-80% of dogs with food allergies. If after 6-8 weeks, the dog has shown some improvement with a strictly followed dietary trial, the diet is then continued until maximal improvement is noted. To confirm the diagnosis, the patient is then given its previous diet. Clinical signs should recur within 7-10 days. If there is no response to a diet trial after 6-8 weeks, then a different type of hypoallergenic diet may be fed. If the dog continues not to respond to the dietary trials, then food allergies are ruled out of the list of possible problems. Further testing may be necessary to determine the correct diagnosis.
   
   Treatment: Proper treatment for food allergic animals is life-long maintenance with a diet that the animal can tolerate without experiencing skin reactions. For life-long maintenance, it is best to have the dog on a high quality, hypoallergenic commercial brand dog food; this is possible in most dogs with food allergies, although some experimentation may be required to find a brand and ingredient combination that will be well tolerated. Occasionally, a dog may need to be maintained long-term with a homemade diet. Vitamin and mineral supplementation may be necessary in such cases to avoid nutritional deficiencies. Corticosteroids may be used in dogs with food allergies as a last resort, although the success of this type of therapy is sometimes poor.
   
   
3. Allergic Contact Dermatitis:
   Introduction: Allergic reactions to substances which directly contact the skin can affect the general condition of the animal or may simply cause a local reaction in the area of contact. Reactions which remain localized to the area of contact are known as contact allergic reactions or allergic contact dermatitis. It may become confusing when a dog experiences allergic contact dermatitis due to a substance which has contacted the entire body such as a shampoo or body rinse. These cases where the problem extends over the entire body may appear at first to be a case of atopy (see above). Generally, most cases of allergic contact dermatitis in dogs are a result of topical medication. Because of this, the history is extremely important in helping the veterinarian pinpoint the cause of the itching.
   
   Causative Agents/Clinical Signs: Many cases of contact dermatitis are caused by medications, shampoos, bedding, chemicals, cleaning agents, or other similar products. When contact is made with these substances, the body’s immune system reacts by changing the skin in the area where the contact is made. The ears, abdomen, thighs, feet, tail, and chin are commonly involved. When an allergic reaction occurs in these areas, the skin is red, inflamed, can be itchy (pruritic), and have bumps or blisters (vesicles).
   
   Diagnosis: To diagnose allergic contact dermatitis, a thorough history is essential. Information on the types of medications or shampoos used recently, bedding type, and any contact with chemicals, cleaning agents, or other similar products is extremely helpful. Skin patch testing and environmental testing are two lines of diagnostics which may be performed by an experienced veterinary dermatologist.
   
   Treatment: The treatment of allergic contact dermatitis focuses primarily on avoiding the substance/medication which led to the reaction. Corticosteroids may be used either systemically or topically to relieve immediate itching and discomfort.

Autoimmune diseases are broken down into primary and secondary disorders. Primary disorders are those which develop spontaneously, independent of any external triggers. Secondary disorders are a result of a triggered response, traceable to a variety of stimulating factors such as certain drugs, bacteria, or viruses. The following will discuss three major types of autoimmune diseases:

Neoplastic (Tumors and Cancer) Skin Problems

Diagnosis: The diagnosis of skin tumors or lumps is based primarily on biopsy or removal of the tumor and subsequent histopathology. Some are possible to diagnose with a fine needle aspirate and cytology. This does not require anesthesia, but a specific diagnosis is usually not possible with this technique.

Treatment: Treatment of skin tumors and malignant cancer types varies with the specific tumor. Removal of the tumor is usually at the top of the list of treatment recommendations. In many cases, removal of the tumor cures the dog. Tumor removal techniques vary a great deal and range from a simple snip excision to amputation of an entire limb. Other treatment recommendations may include radiation therapy, chemotherapy, hyperthermia (heat therapy), and cryotherapy (freeze-burning). Nutritional cancer therapy is a field which has received much attention in the last decade, and prescription diets are commercially available through veterinary hospitals which appear to have benefit in slowing the growth of many types of cancer.

See the information on page E495 for additional details on the diagnosis and treatment of tumors in general.

The following list of tumors and skin cancer types is not meant to cover all the possible skin tumors, but will include many of those most common in the canine patient. The purpose is to give dog owners a brief description of the tumor or skin cancer type after a diagnosis has been made. This list is not intended to provide the diagnosis of a lump or tumor. These tumors and cancers are listed in order of how frequently they are diagnosed in dogs living in the United States.

1. Mast Cell Tumor:
   Introduction: Mast cell tumors (MCTs) are the most common skin tumor in the dog. The average age at diagnosis is 9 years old, although a mast cell tumor has been seen in a 3 month old puppy. Breeds at risk include mixed breed dogs, boxers, Boston terriers, beagles, schnauzers, Labrador retrievers, weimaraners, dachshunds, golden retrievers, pugs, and shar peis.
   
   Clinical Signs: Mast cell tumors of the skin may appear as distinct lumps or as varying sized patches of lumpy skin. They may be slow or fast-growing. Mast cell tumors have the potential to spread internally and cause life-threatening disease. Therefore, it is not a tumor type to be treated lightly. The location of the tumor on the body can indicate how serious the problem might be. The outcome tends to be worse if the tumor is located in the mouth, near the anus, around the prepuce, or in the nail beds.
   
   Diagnosis/Treatment: This is one of few tumor types which can be diagnosed with a fine needle aspirate and cytology. Treatment depends on the location and grade (a score given to MCTs based on histopathology which can strongly predict the outcome) of the tumor. A veterinary oncologist (cancer specialist) may become involved in difficult cases.
   
   
2. Perianal Adenoma:
   Introduction: Perianal adenomas or circumanal gland tumors are very common in male dogs. While they can occur in female dogs, they are far less common. Breeds at risk include dachshunds, German shepherds, beagles, shih tzus, cocker spaniels, English bulldogs, Samoyeds, Lhasa apsos, and Siberian huskies.
   
   Clinical Signs: These tumors are usually small, round, nonpainful, slow-growing lumps located on the hairless skin around the anus. They may be solitary or multiple in number. Usually perianal adenomas are benign and do not cause any problems; however, if the tumor is malignant, it can cause life-threatening illness by spreading to other areas.
   
   Diagnosis/Treatment: A diagnosis must be made by histopathology– it is very difficult to tell the difference between benign and malignant perianal gland tumors with cytology alone. Treatment for the common benign variety may be accomplished with tumor removal or cryosurgery. Castration of intact male dogs is also helpful. Treatment for the malignant type involves aggressive removal and potentially radiation and/or chemotherapy. Multiple surgeries may be necessary for some cases. Malignant circumanal gland tumors in some dogs (especially females) can be incurable, leading to death in some cases.
   
   
3. Lipoma:
   Introduction/Clinical Signs: Lipomas or fatty tumors are common in dogs and usually occur in dogs older than 8 years of age. They are benign growths, originating from fat cells (adipocytes). They are most common on the thorax, abdomen, and front legs. Breeds at risk include cocker spaniels, weimaraners, Labrador retrievers, dachshunds, Doberman pinschers, miniature schnauzers, and small terriers.
   
   Diagnosis/Treatment: Lipomas can be best diagnosed by histopathology. Cytology can be a useful diagnostic tool as well; however, many tumors contain fat cells, and cytology alone may lead to an incorrect diagnosis of a lipoma. The ideal treatment for lipomas is surgical removal of the tumor. In overweight animals, a restricted diet for some weeks prior to surgery may help reduce the size of the lipoma and improve the surgeons ability to distinguish the tumor from surrounding tissues. This will greatly reduce surgery time and increase the chances of completely removing the tumor.
   
   
4. Sebaceous Gland Tumors:
   Introduction: Sebaceous glands are found throughout the skin, especially in areas that require moist and pliable skin, such as the eyelids and lips. They are also found in between foot pads, on the chin, and on the tail, where they may have scent-marking functions. Sebaceous glands produce an oily substance that keeps skin moist and healthy. Tumors of these glands are common, most often occurring in dogs 9 years of age and older. Breeds at risk include cocker spaniels, dachshunds, Irish setters, miniature schnauzers, beagles, Siberian huskies, poodles, shih tzus, Lhasa apsos, and malamutes.
   
   Clinical Signs/Diagnosis: There are several types of sebaceous gland tumors, most of which are benign. These tumors often appear as white to pink, raised, cauliflower-like growths commonly occurring on the limbs, head, trunk, and eyelids. Diagnosis is by histopathology, although clinical appearance and cytology may also establish a fairly accurate diagnosis.
   
   Treatment: Proper treatment may include surgical removal, cryotherapy, or observation without treatment. Malignant sebaceous gland tumors do occur and should be removed surgically as soon as possible. However, these malignant tumors rarely spread beyond the original tumor area.
   
   
5. Fibrosarcoma:
   Introduction/Clinical Signs: Fibrosarcomas are aggressive, malignant tumors that occur anywhere on the body, but more commonly on the limbs and the trunk. Golden retrievers, Doberman pinschers, and cocker spaniels are breeds at risk. Fibrosarcomas are usually irregular, firm, sometimes lumpy growths that often do not have distinct borders. They generally grow rapidly and may ulcerate and drain at the surface.
   
   Diagnosis/Treatment: Diagnosis is accomplished by histopathology. Cytology may help identify the typical spindle-shaped cancer cells which make up fibrosarcomas, but large areas of hemorrhage and tissue death commonly found inside the tumors may yield confusing cytology results. Treatment begins with aggressive surgical removal. Radiation therapy, chemotherapy, and cryotherapy may be helpful in some cases.
   
   
6. Melanoma:
   Introduction/Clinical Signs: Melanomas are tumors arising from pigmented cells and are usually found as black, gray, or brown growths. They occur most commonly on the head, limbs, toes, scrotum, lips, mouth, thorax, and abdomen. Breeds at risk include schnauzers, Airedale terriers, Boston terriers, Scottish terriers, boxers, Chihuahuas, chows, springer spaniels, cocker spaniels, Doberman pinschers, golden retrievers, and Irish setters.
   Melanomas may occur as benign or malignant growths. Malignant melanomas are tumors with a risk of spreading and causing aggressive destruction of internal organs. This is especially true if the tumor originates in the mouth or nail beds.
   
   Diagnosis/Treatment: Histopathology is the primary method of diagnosis. Aggressive surgical removal of the tumor is the treatment of choice, although spreading of the tumor may already have occurred at the time of diagnosis. The average survival time in one group of dogs with melanomas located inside the mouth was 3 months following surgical removal. Radiation therapy and chemotherapy have been used with varying success.
   
   
7. Histiocytoma:
   Introduction: Histiocytomas are common benign tumors which tend to occur in young dogs. Breeds at risk include boxers, dachshunds, cocker spaniels, rottweilers, Great Danes, schnauzers, shar peis, Boston terriers, Shetland sheepdogs, Labrador retrievers, and Doberman pinschers.
   
   Clinical Signs: These are solitary, firm, round or disk-shaped and tend to occur on the head, limbs, and ears. They frequently ulcerate at the surface and may grow surprisingly rapidly for a benign tumor. Occasionally, this tumor type may occur in groups and may even spread to lymph nodes– this type of histiocytoma is probably more common in shar peis.
   
   Diagnosis: A diagnosis is made based on histopathology. Because of its rapid rate of growth that is not typical of benign tumors, histiocytomas often appear as malignant cancer. It is usually a great relief to have a report of histiocytoma come back from a pathologist after the cytology seemed to indicate a malignancy.
   
   Treatment: The majority of histiocytomas recede on their own within a few months. Surgical removal is curative, and cryotherapy has also been successful at treating histiocytomas. In cases where surgical removal is difficult due to location on the body, but the tumor is causing discomfort or has become infected, the use of a topical corticosteroid with dimethyl sulfoxide (DMSO— a powerful medication which helps other drugs cross skin barriers they otherwise would not) has been very successful.
   
   
8. Squamous Cell Carcinoma:
   Introduction/Causative Agents: Squamous cell carcinoma (SCC) is probably the condition most frequently associated with the term "skin cancer." SCC arises from the most superficial layer of skin and is associated with exposure to excessive sunlight, virus infections of the skin, radiation, burn and frostbite scars, and chronic skin irritation. Unmanaged discoid lupus erythematosus of the nose may also develop into SCC.
   
   Breeds at risk include Scottish terriers, Pekingese, boxers, poodles, and Norwegian elkhounds.
   
   Clinical Signs: One form of squamous cell carcinoma affects the nail beds and causes a painful swelling of the toe. This form more commonly affects a different set of dog breeds. These are usually large breed dogs with black coats such as Labrador retrievers, Bouvier de Flandres, standard poodles, and giant schnauzers. Sunlight-induced squamous cell carcinoma occurs in breeds with short, white hair coats such as dalmations, beagles, and bull terriers. SCC can occur on the trunk, limbs, toes, scrotum, lips, anus, and nose. Skin in which squamous cell carcinoma arises may appear as an open sore or wound that does not heal, or may occur as cauliflower-like nodules of varying size. Toes which are affected may be swollen, painful, and have the toenail fall off. SCC is a locally aggressive malignant cancer. This means that surrounding tissues are often damaged and destroyed. Lymph nodes may be affected locally in some cases.
   
   Diagnosis/Treatment: Histopathology is necessary for a diagnosis. Radiographs of SCC of the toe are helpful because they may identify if bone is affected and if the swelling is more than an infection of the soft tissues. Treatment of SCC may include surgical removal of the cancer, cryotherapy, hyperthermia, or radiation therapy. Amputation of a toe affected with SCC will usually cure the cancer, although the amputation may need to be aggressive, with the location of the amputation one knuckle joint above any affected tissue. Amputation of the affected portion of the nose ("nosectomy") is required in SCC resulting from unmanaged discoid lupus erythematosus. The cosmetic result is often surprisingly acceptable, and the surgery will usually cure the problem. In all cases, it is important to avoid additional exposure to sunlight. This is critical because new squamous cell carcinoma development is common in dogs that have already been diagnosed with the disease if ultraviolet light is not avoided.
   
   
9. Hemangiopericytoma:
   Introduction/Clinical Signs: Hemangiopericytomas are skin tumors which occur frequently in older dogs on the limbs, especially the knee (stifle) and elbow joints. They tend to be firm, lumpy, raised masses of varying sizes. Breeds at risk include boxers, German shepherds, cocker spaniels, beagles, Irish setters, springer spaniels, Siberian huskies, and collies. Hemangiopericytomas rarely spread to other areas of the body. They may be difficult to completely cure because they can recur following surgery. With each recurrence of a hemangiopericytoma, they appear more aggressive and become even more difficult to cure. The longer a hemangiopericytoma has been present prior to surgery, the more likely it is to recur.
   
   Diagnosis/Treatment: Histopathology is the diagnostic test of choice for diagnosis. Treatment is accomplished by surgical removal and/or amputation of the affected limb. Radiation therapy has also been somewhat effective in certain cases.
   
   
10. Basal Cell Carcinoma:
    Introduction: Basal cell carcinomas are a large class of tumors arising from skin and a few other tissues. These tumors are associated with exposure to ultraviolet light in people, but this correlation has not been proven in dogs.
    
    Clinical Signs: These tumors are usually slow-growing, firm, rounded, and may ulcerate on the surface. Basal cell carcinomas are also frequently pigmented and may have the appearance of a melanoma. While the term "carcinoma" implies a malignant growth, basal cell carcinomas are considered to have a low grade of malignancy and rarely spread beyond the immediate area.
    
    Diagnosis/Treatment: Histopathology will identify this type of tumor. Treatment may be achieved by surgical removal of the tumor or cryotherapy.
    
    
11. Papilloma:
    Introduction/Clinical Signs: Papillomas or warts are common in dogs and occur in a variety of ways. Cauliflower-like pink to white multiple or solitary lumps may occur on the head, eyelids, feet, abdomen, groin, and mouth. This tumor type results from skin infections of papillomaviruses. Breeds at risk include schnauzers, cocker spaniels, kerry blue terriers, and shar peis. A rather severe form of this problem is known as canine oral papillomatosis. Papillomatosis causes the mouth and throat tissues of young dogs to become covered with white, cauliflower-like masses. This form of papillomas does not appear to have any breed preferences and can affect any dog. Papillomavirus infection of the skin has also been associated with the development of squamous cell carcinoma.
    
    Diagnosis/Treatment: Histopathology is the diagnostic tool most often utilized to establish a certain diagnosis; however, papillomas are often diagnosed visually upon close inspection. Treatment of papillomas can include surgical removal, cryotherapy, and observation (no treatment). Canine oral papillomatosis usually resolves on its own within 3-4 months. Use of retinoids or interferon therapy may help improve recovery times.
    
    
12. Hemangioma/Hemangiosarcoma:
    Introduction/Clinical Signs: Hemangiomas of the skin are benign tumors arising from the lining of small blood vessels. These tumors appear as well defined, rounded, blue-black to red masses of varying firmness and size. Hemangiosarcoma is the malignant and, fortunately, less common cousin of the hemangioma. Hemangiosarcomas appear as blue-black to red masses, often with a bruised appearance. They tend to be closely associated with surrounding normal tissue and may grow to be incredibly large. Breeds at risk include boxers, golden retrievers, German shepherds, dalmations, beagles, springer spaniels, Bernese mountain dogs, basset hounds and pointers. Long term exposure to sunlight may lead to hemangioma and hemangiosarcoma formation in the sparsely-haired areas of light-skinned dogs. Hemangiosarcomas may arise from internal organs, especially from the liver and spleen, and then spread to the skin; therefore, it is important to fully research the possibility of internal original tumors when a skin hemangiosarcoma is diagnosed.
    
    Treatment: Aggressive surgical removal is considered the therapy of choice; however, the prognosis for dogs with hemangiosarcoma is usually poor because the cancer is extremely aggressive and spreads quickly to other tissues. Chemotherapy has also been used as a treatment option with some success.
    
    
13. Lymphoma:
    Introduction: Lymphoma is a malignant cancer of the lymphocytes. (Lymphocytes are cells that are important to the immune system in fighting infection.) Any tissue with lymphocytes can be affected, including the skin. There are several classes of lymphoma, including a condition known as "mycosis fungoides." Many years ago a skin condition unlike most types of cancer was originally thought to be a fungal infection. This condition has since been shown to be lymphoma in a form which appears much like immune-mediated skin disease or a skin infection. The name "mycosis fungoides" has never been changed, although it is misleading because it implies a fungal infection.
    
    Clinical Signs: Lymphoma can appear as solitary or multiple skin masses or plaques and may affect nearly any part of the skin. The nose, mouth, footpads, genital areas, anus, and any haired or non-haired area of skin may be involved. Mycosis fungoides can appear as reddened, itchy, scaly skin across large areas of the body. It can also appear as ulcerations, crusting, swelling, irritation, and loss of pigment around the nose, eyes, and lips, much like pemphigus complex.
    
    Diagnosis/Treatment: The diagnosis of lymphoma is made by biopsy and histopathology of affected areas. Prognosis for dogs with lymphoma of the skin is poor and is considered grave for dogs with the mycosis fungoides form. Surgical removal of the cancer in these cases is not possible because such extensive areas of the body are usually involved. Chemotherapy and different combinations of drugs are sometimes successful. For mycosis fungoides, topical application of nitrogen mustard (mechlorethamine) is used successfully in treating the irritated skin part of this disease. Even though most dogs experience an improvement in the clinical signs, there is no evidence that this therapy extends the lifespan of a dog diagnosed with mycosis fungoides. Retinoid therapy has been used, but with unpredictable success.

Introduction: These are skin abnormalities caused by problems with the organs that excrete hormones and related substances. These disorders are encountered on a relatively regular basis in dogs. Three of the most common endocrine diseases affecting the skin will be discussed:

1. Hypothyroidism:
   Introduction/Clinical Signs: Hypothyroidism is the most common endocrine disease seen in dogs affecting the skin. Signs of skin disease tend to develop slowly over several months. Initially, alopecia (hair loss) is usually seen over the animal’s trunk, tail (giving a "rat tail" appearance), thighs, or flanks. In time, the alopecia worsens, becoming symmetrical, but tends to spare the head and limbs. Hair often fails to regrow after clipping or shaving. The hair coat in general tends to appear dull, dry, and brittle. Scale (dandruff), increased skin pigmentation, and thickened skin are common. Secondary bacterial, parasitic (mites), or fungal (yeast) skin infections are also very common. If pruritus (itching) is present, it is primarily due to the secondary infections.
   
   Diagnosis/Treatment: The general diagnosis and treatment of hypothyroidism is discussed elsewhere (see page F815). The skin disorders related to hypothyroidism do respond to treatment. Once treatment is started, the skin problems tend to worsen before showing signs of improvement. Significant hair regrowth can be seen within 4-6 weeks of beginning treatment, although it may take 4-6 months for hair regrowth to be complete.
   
   
2. Hyperadrenocorticism:
   Introduction/Clinical Signs: Hyperadrenocorticism or Cushing’s disease may occur naturally or may be iatrogenic (caused by people) because of long-term use of glucocorticoid therapy. Skin changes may begin as an unhealthy appearance of the hair coat. Owners may find that grooming appointments are not needed as frequently because the hair is not growing as fast as it normally does. The coat may change color early on, with black and brown hairs lightening to rust or tan. Hair is eventually lost, leading to symmetrical hair loss over the trunk. The skin tends to become thin and wrinkled, heals slowly from cuts and scrapes, and bruises easily. Secondary skin infections (bacterial, fungal, parasitic) are common.
   
   Diagnosis/Treatment: Skin disorders related to Cushing’s disease respond variably to treatment. Improvement is usually noted, but may not be complete even in well-managed dogs. See page F138 for an in-depth discussion of Cushing’s disease including diagnosis and treatment.
   
   
3. Diabetes mellitus: While skin-related problems due to diabetes occur only in a minority of cases, diabetes is a relatively common disorder in dogs. When skin disease does occur in association with diabetes, secondary skin infections are the biggest problem. Varying degrees of hair loss, scale (dandruff), and thin skin may also be noted. These abnormalities may or may not be correctable through the proper treatment of diabetes. See page F153 for additional details on diabetes.

1. Seborrhea:
   Introduction: The term "seborrhea" is used to describe a defect in either production of sebum (normal skin oils) or keratinization (normal growth and turnover of skin cells), or a combination of both. Abnormalities can occur with both quality and quantity of sebum. Generally, seborrhea is a secondary condition seen in association with an underlying primary cause such as allergic skin disease or endocrine-related skin disorders. Primary seborrhea does occur, but it is uncommon.
   
   Types of seborrhea:
   1. Seborrhea sicca: Seborrhea sicca is thought to be a result of decreased sebum/oil production leading to dry, dehydrated skin. The hair coat is dull and the skin is dry with "scale" (white or gray flakes of dry skin found in hair coat). Seborrhea sicca is the most common form of seborrhea seen in dogs.
   2. Seborrhea oleosa: With this problem, excessive sebum/oil production in the skin causes a thick, greasy, sticky hair coat. This condition is usually very messy and can emit a foul odor.
   3. Combination seborrhea sicca/oleosa: The hair coat appears dull like seborrhea sicca, but feels greasy like seborrhea oleosa. This is probably due to increased production of a poor quality sebum. The increased quantity of sebum creates the greasy feel to the hair coat, but the abnormal quality of sebum still allows drying of the skin.
   
   Treatment: The treatment of seborrhea focuses on treating or correcting the underlying cause. Moisturizing shampoos/conditioners that contain sulfur/salicylic acid are extremely helpful with seborrhea sicca (see page G750). Seborrhea oleosa can be managed with a de-greasing shampoo/conditioner that contains benzoyl peroxide or coal tar (see page G659).
   
   
2. Nutritional Skin Disorders:
   Introduction: A number of nutritional deficiencies or excesses can lead to skin disease. Notably among these are deficiencies of vitamins A, B, and E, fatty acids, protein, and zinc; or excessive levels of vitamin A.
   
   
1. Vitamin A: Vitamin A is stored very well in the body. Because of this, excesses of vitamin A are probably more of a concern than is vitamin A deficiency. Both vitamin A deficiencies and excesses cause similar skin problems. Poor hair coat, scaling (seborrhea sicca), hair loss, and secondary skin infections are commonly seen. One major difference between cases of vitamin A deficiency and vitamin A excess is that pain is sometimes noted during the physical exam of a patient with vitamin A toxicity. This is due to bone changes in the spine. Vitamin A can be given as a single injection or with low-dose oral therapy. Oral therapy tends to be expensive, but sometimes necessary for certain cases.
   
   
2. Vitamin B: Vitamin B deficiencies often cause seborrhea sicca with varying degrees of hair loss. Vitamin B is manufactured by bacteria found in the intestine and is constantly absorbed over time. It is not stored in the body, so vitamin B excesses do not occur. Any disease affecting the intestine’s ability to absorb nutrients or affecting the population of bacteria found in the intestine has the potential to result in vitamin B deficiency. Because it affects the bacteria found in the digestive tract, prolonged antibiotic therapy may also result in a vitamin B deficiency. Supplementation with vitamin B products in any dog with chronic seborrhea failing to respond to therapy may be very helpful.
   
   
3. Fatty acids: Fatty acid deficiency may be seen in dogs fed only dry, commercial foods that have been improperly preserved or stored. It can also be seen in dogs fed homemade diets. Skin disorders resulting from fatty acid deficiency are seen several months after starting the diet. Fatty acid deficiency leads to skin thickening, seborrhea sicca, seborrhea oleosa, hair loss, and secondary skin infections. Supplementation with essential fatty acid capsules or household oils (i.e. corn oil, sunflower oil, or canola oil) may correct the problem, but it is generally better to upgrade the diet to one of higher quality. Sometimes, fatty acids are withheld purposely for certain medical conditions such as pancreatitis and obesity. In these cases, the seborrhea and skin infections may have to be treated without correcting the fatty acid deficiency.
   
   
4. Vitamin E: Naturally occurring vitamin E deficiency is rare in dogs. Some cats fed exclusively high-fat diets do suffer from vitamin E deficiency, and the same is theoretically possible for dogs. Some laboratory dogs have been experimentally made to suffer from vitamin E deficiency. These dogs showed signs of seborrhea (seborrhea sicca at first, followed by seborrhea oleosa) and inflamed, itchy skin. They responded dramatically to oral vitamin E supplementation. Topical vitamin E oils are frequently used in a variety of skin diseases in dogs, sometimes with surprising success.
   
   
5. Protein deficiency is unusual because most dog foods now available contain adequate or even high protein levels. However, some diets may be low in protein in order to treat another condition such as kidney failure. Homemade vegetarian diets may also lead to protein deficiency in dogs. Protein deficiency leads to color changes in the hair coat (lightening of darker hair), skin thickening, hyperpigmentation (darkening) of skin, and patchy hair loss. The coat is brittle, dry, and rough. The changes are usually symmetrical over the trunk, legs, head, and feet. Supplementation with protein generally provides a good response.
   
   
6. Zinc-responsive dermatosis: There are two types of zinc-responsive dermatosis syndromes seen in certain dog breeds. The first type (Syndrome I) occurs in Siberian huskies, Alaskan malamutes, and sometimes in Bull terriers. Skin disease usually begins to occur by age 3 and appears as crusting, redness, and swelling with drainage around the eyes, mouth, chin, and ears. Genital areas may be occasionally affected. The condition seems to develop regardless of diet, which is why the disease is not referred to as a zinc deficiency. Because the disease is probably inheritable, it is not recommended that affected dogs be bred.
   
   The second type (Syndrome II) occurs in quickly growing puppies fed diets low in zinc or diets oversupplemented with other vitamins and minerals that interfere with zinc absorption. Inflamed callouses tend to form over bony areas, with deep crevasses and drainage. Secondary infections may occur, and lymph nodes may become enlarged and painful.
   
   Zinc levels can be measured in hair or blood, but are not very reliable. Treatment consists of supplementing the diet with zinc sulfate, zinc methionine, or zinc gluconate. In Syndrome II, once the skin appears normal again and the dietary cause of the problem has been corrected, zinc supplementation may be stopped. Zinc supplementation is usually lifelong for Syndrome I. Some Siberian huskies do not respond to oral zinc therapy and must receive periodic zinc-containing injections.