F770
Skin Diseases

Introduction: Skin problems in cats are a common reason for a visit to a veterinary clinic. This discussion will review many of the most common skin problems seen in cats. 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 and 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. Cats infrequently experience bacterial pyoderma. There is almost always an underlying reason for the presence of a bacterial skin infection in cats; however, this underlying primary cause is not always found.

Feline acne is a specific condition affecting the chin area of cats. The cause of feline acne is not completely known. The infection can be superficial, with small black scabs and crusts found periodically on the chin. It can also be deep, with a painful swelling of the chin area and drainage of a mixture of blood and pus. Diagnosis is easily made based on location and appearance of the condition. Sometimes, an impression smear will be performed by a veterinarian to determine the type of bacteria causing the infection. Treatment for mild, superficial cases may consist of topical therapy only. Antibiotic/antifungal creams such as Dermalone and benzoyl peroxide shampoos or gels may be applied with some success. For severe, deep infections, oral antibiotics such as Antirobe may be necessary.

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Introduction: There are several types of fungi that can infect the skin of cats. 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.

Parasitic Skin Infections:

1. Fleas:
   
   Introduction: Fleas and flea allergies are among the most common external parasite skin diseases seen in cats. Because fleas do better in hotter, more humid environments, they are more of a concern in some areas than others. The cat flea, Ctenocephalides felis, spends its entire adult life on the cat. The entire flea population living on any single cat consists of approximately 95% egg and larval stages, with adult fleas making up the remaining 5%. Thus, it may be difficult to find the adult fleas on a patient, even though the cat may suffer from a significant flea problem.
   
   Clinical Signs: A range of problems may be seen in cats with flea infestations. Minor infestations may go unnoticed in some cases or may cause some itching (pruritus). In the very young or debilitated animal with more severe infestations, blood loss may be significant enough to cause anemia. Allergic reactions to the flea bite and secondary infections with tapeworms are also common. Cats that develop fleabite hypersensitivity or miliary dermatitis usually suffer severe itching (pruritus). They may develop hair loss, thickened and/or discolored skin, and secondary bacterial infections. Only one to two flea bites per week may be sufficient in supersensitized pets to perpetuate the problem. Cats with underlying allergies (atopy, food sensitivity) are prone to fleabite hypersensitivity.
   
   Diagnosis: Diagnosis of a flea infestation is usually made by noting the actual fleas or flea dirt (feces) on the skin of the animal. Pinpointing a fleabite hypersensitivity problem, however, can be more challenging, since a very minor infestation may be all that is present in such cases.
   
   Crusting, open sores may be noted at the base of the tail and around the neck of a cat with an allergic reaction to flea bites. Flea combs may be used by veterinarians or pet owners to comb out evidence of fleas. Flea dirt is often combed out and can be distinguished from other debris by placing the suspected flea dirt on a moistened napkin. Because flea dirt is the excrement from a parasite that consumes blood, it will leave light red stains on the napkin.
   
   Other tests, including a blood sample (CBC) and skin biopsies, can be used to help identify fleabite hypersensitivity. A specific type of white blood cell called an eosinophil is commonly seen in both a CBC and in a skin biopsy. Another aid for a veterinarian in the diagnosis of fleabite hypersensitivity can be injecting the flea allergen directly into the skin and looking for an immediate reaction.
   
   Finally, specific flea treatment products may be administered, followed by observation to see how the cat responds to the treatment. If the pet responds favorably, a diagnosis of flea infestation can be made. Using treatment as a "diagnostic approach" can be justified because most treatment products are generally considered safe and affordable.
   
   Treatment/Prevention: Treating flea infestations primarily focuses on removal of the fleas from both the animal and the animal’s living environment. First, eliminate fleas from the animal. There are many available products. Some are obtainable through a pet store (over the counter), while others are prescription drugs and are obtainable only through a veterinarian. Over the counter products that may be helpful include flea combs, flea collars, sprays, dips, powders, and shampoos. Insecticidal flea collars are generally more effective than ultrasonic collar devices at reducing flea infections. Sprays usually have rapid action but may be difficult to apply in a thorough and consistent manner. Flea dips are generally rapid-acting and long-lasting; dips may be given through a pet grooming facility or at home. Flea powders are effective but messy and usually vary on how long they will last. Flea shampoos are usually good for rapid killing of fleas but have no residual (lasting) benefits. In general, using the over-the-counter products alone is probably insufficient for adequately treating a cat with fleabite hypersensitivity. Prescription products available through a veterinarian are usually of great benefit to cats with fleabite hypersensitivity problems. These products can be used for treatment and prevention. Many of these products not only kill fleas but are effective against a variety of other parasites including ticks, mites, intestinal parasites, and heartworm larvae. Monthly pour-on (drip-on) formulations that are available include Frontline, Advantage, and Revolution. Oral tablets are also available and include Program and Capstar.
   
   Second, it is important to eliminate fleas from the pet’s living space. This is accomplished with a thorough washing of carpets, rugs, and bedding, followed by vacuuming furniture, baseboards, and even calling in a commercial exterminator in more severe situations. Some advocate the use of foggers; however, foggers may not be effective under furniture, and it is usually necessary to utilize one fogger per room of the house. Some products, such as Program, may be used on the affected animal(s) in order to prevent flea development and keep the eggs from hatching in the environment. An effective treatment plan must involve three things: treating the pet’s environment, treating the affected pet, and treating all other pets that have contact with the affected pet. Failure to thoroughly address all three of these areas can result in continued and repeated flea infestations. (See F998  for information on flea problems in humans and pets.)
   
   
2. Ticks:
   
   Introduction: Ticks are a common bloodsucking ectoparasite that can cause skin disease in cats. 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 as much as the diseases they can transmit. Ticks are responsible for transmitting a large number of microbial diseases to cats and other species, including man. Some of the diseases ticks are responsible for transmitting may be life-threatening to cats and people. Babesiosis (piroplasmosis), Cytauxzoonosis, feline ehrlichiosis, tularemia, Q fever, and possibly Lyme disease are all infectious diseases that are transmitted by ticks to cats.
   
   Clinical Signs/Diagnosis: Ticks may attach themselves to any part of a cat and often cause a local inflammatory reaction in the skin at the site of attachment. When attached to an external location on the cat, 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 yet 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 that 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 under prevention.
   
   Prevention: Treatment for the various microbial diseases ticks can transmit is often complicated and costly. Sometimes, the pet may die in spite of aggressive treatment. Because of this, prevention of tick infestations is of great importance. A variety of quality products exist that may be administered before a pet is taken into an area known to harbor ticks. Over the counter products that 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, 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 and Revolution. (Specific information on both of these products can be found in Section C of this manual.)
   
   
3. Mites:
   
   Introduction and Causative Agents: Two types of mite infections occur frequently in cats. Notoedres cati, the mite responsible for notoedric mange, and Cheyletiella blakei, the mite responsible for cheyletiellosis, are both common in cats. Other mites such as Demodex species and chigger mites occasionally can also cause disease. The ear mite, Otodectes cynotis, is also a very important mite infection in cats, generally limited to the ear canal.
   
   Note: The use of ivermectin in some of the following treatments is considered "extra-label;" therefore, a veterinarian must be consulted before administering it to a cat.
   1. Notoedric mange: Notoedres cati is a sarcoptic mite that causes a skin disease in cats similar to sarcoptic mange in dogs. This mite is very contagious and can also infect dogs, rabbits, and humans. Notoedric mange usually starts with itchiness and scratching at the head, ears, and neck, with crust formation. Later, the disease may spread to other areas of the body, especially the legs and the groin area. Secondary damage to the skin from the cat’s own scratching often leads to secondary bacterial or fungal infections. Lymph nodes may be swollen and tender.
      
      Diagnosis of notoedric mange is usually made with skin scrapings that are then examined using a microscope. If the diagnosis cannot be made with a skin scraping, skin biopsy and histopathology can also be helpful.
      
      Treatment of notoedric mange in cats begins with clipping and cleaning of the affected areas. Lime sulfur dips can be used to cure this infection. They are given once weekly until the skin is back to normal. Another treatment option involves giving two or three ivermectin injections. Revolution can be used in an extra label manner to treat cats with notoedric mange. Treatment of all cats on the same premises is critical in preventing this disease from recurring.
      
      
   2. Cheyletiellosis: Cheyletiella blakei is a rather large mite that tends to cause flaking and dandruff on the back of cats. As the mites move, the large flakes of dandruff will move around as well. Because this movement is visible to the naked eye, the term "walking dandruff" is used. Cheyletiellosis can also affect dogs, rabbits, and humans. Itching ranges from completely absent to severe. Scaling (dandruff) is very common with cheyletiellosis, and its presence can be very helpful in making a correct diagnosis.
      
      Diagnosis of cheyletiellosis is made by direct observation of the mites and/or their eggs. Mites and eggs may be collected from an infected individual by skin scrapings, tape preparations, combings, vacuum techniques, or analysis of the feces.
      
      Treatment of cheyletiellosis may include weekly lime sulfur dips for 3-6 weeks, oral ivermectin treatments weekly for 4-6 weeks, or subcutaneously injected ivermectin every 2 weeks for 3 treatments. Many medications used to control fleas may also be successful at treating Cheyletiella blakei infections. Because this mite can live off of the host for a longer period than most mites, maintaining a clean environment is very important in successful management of this type of mange. Frequent vacuuming of carpets and rugs, washing of the bedding, and treatment of all dogs and cats in contact with an infected pet are all important in helping to prevent re-infection of treated animals. For more information on mites in humans and pets, see F998.
      
      
   3. Demodectic mange (demodecosis):
      Feline demodecosis is uncommon. Demodex cati, Demodex gatoi, and an unnamed species of Demodex are found in cats with this mange mite infection. Cats suffering from demodecosis usually have patches of hairless, reddened, itchy skin with crusts. Localized Demodex infections are most common, but generalized infections can also occur. Purebred Siamese and Burmese cats seem to have more problems with generalized demodecosis than do other cat breeds. Sometimes, cats may suffer from Demodex infections of the ear canals. Demodex gatoi is contagious to other cats; therefore, all household cats should be treated when any case of feline demodecosis is diagnosed.
      
      Diagnosing demodectic mange is accomplished by first taking 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 relatively deep in the hair follicles (although not as deep as the dog variety of Demodex mite). 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.
      
      Because Demodex mites infecting cats do not appear to burrow as deeply into the skin and hair follicle, successful treatment in cats is usually easier than it is in dogs. Topical products like benzoyl benzoate ointment (Goodwinol ointment), lime sulfur dips, and carbaryl shampoos can be used with success. Weekly amitraz dips can also be helpful. Ivermectin injections have also been used in treatment, although not as frequently as with demodecosis in dogs. Antibiotics may be used if secondary bacterial infection occurs.
      
      
   4. Otodectes cynotis is a common mite that is found mainly in the ear canals and adjacent skin of cats, dogs, and ferrets. Dark waxy debris is common with infestations of Otodectes cynotis, and intense itching of the ears usually accompanies such infections. Some cats that suffer from ear mites may shake their heads so violently because of irritation that they develop an aural hematoma (a very painful swelling of the ear pinna or thin part of the ear). Secondary ear infections with bacteria and/or yeast are common with ear mites.
      
      Diagnosis of ear mite infections is made by observing the mites using a microscope. A cotton-tipped swab is placed into the ear canal and a sample of the dark waxy debris is collected and examined under magnification.
      
      Many treatments for ear mites exist, some of which can be found over the counter in pet shops and stores. Because ear mites are very contagious between animals, it is important to treat all in-contact dogs and cats as well as the affected pet. Regardless of the treatment selected, a thorough cleaning of the ears is the first step to clearing up an ear mite infection. Rotenone-based ear drops or washes can be used with some success. Ivermectin administered either subcutaneously or directly into the ears may also be used, but results are unpredictable. Finally, selamectin (Revolution) has recently been approved for treatment of ear mites in cats and kittens, and it appears to be a very safe, effective, inexpensive, and simple means of treating Otodectes cynotis infections.
      
      
4. Lice:
   
   Introduction and Causative Agents: Most lice are extremely species-specific, which means that they are adapted to one type of host animal (or human) and are unlikely to be contagious to other species of animals. They can be, however, very contagious to other individuals within the same species. Felicola subrostratuas is a chewing louse adapted to cats.
   
   Clinical Signs: Lice are parasites of the skin that cause mostly superficial skin inflammation and itching. Some cats infected with Felicola subrostratuas can suffer severe itching and hair loss on the back.
   
   Diagnosis: Diagnosing an infestation with lice is made by identifying the parasite using a microscope. Careful observation of the anatomy of the louse will aid a professional in identifying the specific species causing the infection. This is important in order to determine the most likely source of the louse infection and to aid in preventing re-infections.
   
   Treatment: Treatment of lice infections in cats is accomplished with the use of carbaryl shampoos or dioxathion shampoos, sprays, or dips. Usually, treatment is administered and repeated weekly until the lice infestation has resolved. Two or three treatments are usually sufficient. Fipronil (Frontline) sprays can also be effective in cats.
   
   

Introduction: Allergic skin disease can occur in cats but does so less frequently than in dogs. Allergic skin disease is broken down into three major categories based on how the offending substances that cause the allergic reaction enter the body. Recently, how these category headings are broken down has come into some controversy. This is because a given substance that causes an allergic reaction may actually enter the body through many different avenues. It is actually quite important to understand this when treating an allergic skin condition. In general, allergies result from an exaggerated response to a foreign substance (allergen) that the immune system perceives as a threat to the body.

1. Atopic or Allergic Inhalant Dermatitis:
   
   Introduction: The term allergic inhalant dermatitis implies that the cat has inhaled the substance(s) that causes 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 commonly used to describe these types of allergic reactions. Atopy is often considered an inherited problem passed on through genetics. All cat breeds and both male and female cats appear to be equally affected. Cats younger than 3 years of age seem more likely to become affected.
   
   Causative Agents: Cats can be allergic to a variety of things including flea saliva, house dust, house mites, air-borne molds, human dander, and regional pollens 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 cats with atopy overreacts 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 high levels in cats that 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. Many areas of a cat’s body may be affected depending on the pattern of atopy present. Four reaction patterns occur in cats in response to atopy. The first reaction pattern is called "fur mowing." This is where the cat chews its own hair out, leaving bald, reddened patches all over its body. Secondly, eosinophilic granuloma plaques may occur, in which the skin becomes reddened and thickened and hair falls out. The third type of reaction pattern is called "miliary dermatitis." It is a common secondary reaction to skin infections in the cat and produces crusting and intense itching all over the body. Itching/scratching of the face, ears, and neck in the absence (initially) of any visible skin problem is the fourth reaction pattern. Atopy is usually not seasonal in cats, indicating that cats tend to react more to house mites and other nonseasonal allergens.
   
   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 cats suffering from atopy. Because the testing is usually expensive, and the results can be difficult to interpret, it should be reserved for cats that are experiencing the most severe reactions.
   
   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 cats are known to react directly into the skin. Allergic cats will react by forming a lump or "wheal" in the area associated with the specific injection(s). 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 test injections. 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 that 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 cat 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 cat 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 cat may be reacting. These tests measure IgE levels in the animal’s blood and report any allergens where there is a high IgE response.
   
   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 cat’s immune system to the allergen or allergens that cause the allergic reaction. In order to offer this type of therapy, either intradermal skin testing or serologic allergy testing must be performed to specify the exact offending allergens to be desensitized against. The way hyposensitization works is fairly 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. While considered as probably the best treatment option by many for controlling atopy in cats, hyposensitization treatment is not often used. Further research needs to be done in the area of immunotherapy to help better understand all the factors that 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 antiinflammatory drugs that are commonly used in the control of atopy. Corticosteroids given systemically (orally or by injection) are necessary to help control atopy in a large number of cases. Cats tend to require higher dosages of corticosteroids than dogs do for an adequate response.
         
         Prednisone, prednisolone, methylprednisolone, triamcinolone, and sometimes dexamethasone can be used in cats. Corticosteroids are generally inexpensive but can 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. Steroid injections given weekly to every few months may be sufficient to manage a cat with atopy. Oral steroids may also be used in cooperative cats on a daily to twice daily basis. 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. There are several types of antihistamines available. Antihistamines may be synergistic (more effective if given together than separately) with essential fatty acids. Some available antihistamines that 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 cat 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 cat, 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. Perhaps the greatest disadvantage of antihistamine use in cats is the fact that it is an oral medication that requires lifetime administration if used to treat atopy. This, probably more than any other reason, discourages the use of antihistamines in cats.
         
         
      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. EFAs should be given for at least 3 months to observe maximal benefit. 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. 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 most cost-effective is cool-water bathing, which may give relief for up to 1-2 days. Cool-water baths may be very difficult and traumatic for cats, however. Other types of topical therapy include shampoos/conditioners, creams, ointments, and sprays. Shampoos that 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 ointments, shampoos, or emollients such as fatty acids, glycerin, and oatmeal. Sprays may contain antihistamines, corticosteroids, or local anesthetics.
         
         
      5. Dietary therapy: Dietary therapy is generally beneficial to those animals suffering specifically from food related allergies (discussed below). 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 that 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 20% of all skin related allergies in cats. 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 cat to develop an allergy to food, and some cats may eat the same diet for years before they begin to react to an ingredient. Allergens that are most commonly associated with food allergies in cats include beef, dairy products, and fish.
   
   Clinical Signs: The signs of food allergy in cats are similar to atopy. They include moderate to severe itchiness, redness, and skin erosions often restricted to the head, face, and neck. Sometimes, "fur mowing" (self-induced baldness without obvious initial skin problems) and eosinophilic plaques will also occur. Vomiting, diarrhea, and mouth inflammation may accompany skin problems in cats 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, or palatable medications) must be eliminated. The diet itself can be either home-made or commercial, but it must contain only carbohydrates as a base and one protein type to which the cat has never or only rarely been exposed. Such protein sources can include lamb, rabbit, or venison. Rice or potato may be added but are usually avoided by the cat. Homemade diets are usually the best. Commercial hypoallergenic diets can be used for the dietary trial but are less successful since there is no commercial diet that works for all cats with food allergies. If after 6-8 weeks, the cat 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 cat 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, a different type of hypoallergenic diet may be fed. If the cat continues not to respond to the dietary trials, food allergies are not likely the cause, and further testing is necessary to find 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 feed the cat a high quality, hypoallergenic commercial brand food or a balanced homemade diet. Many cats with food allergies will do very well on a commercial hypoallergenic brand of food, although some experimentation may be required to find a brand and ingredient combination that will be well tolerated. Cats fed a homemade diet often require vitamin and mineral supplementation to avoid nutritional deficiencies. Corticosteroids may be used if a restricted diet is not successful or not possible (i.e. cats that hunt for their own diets).
   
   
3. Allergic Contact Dermatitis:
   
   Introduction: Allergic reactions to substances that 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 that remain localized to the area of contact are known as contact allergic reactions or allergic contact dermatitis. It may become confusing when a cat experiences allergic contact dermatitis due to a substance, such as a shampoo or body rinse, that has contacted the entire body. These cases where the problem extends over the entire body may appear at first to be a case of atopy (see F770). Contact dermatitis is considered rare in cats, with the possible exception of miliary dermatitis. Miliary dermatitis, discussed previously as one of four reaction patterns in feline atopy, may be thought of as a type of contact dermatitis in which the skin reacts to the presence of an infection such as fleas or fungus (dermatophytes).
   
   Causative Agents/Clinical Signs: Many cases of contact dermatitis are caused by infections, 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, back, thighs, feet, tail, and chin may become 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, any ongoing infections the cat may be experiencing, bedding type, and any contact with chemicals, cleaning agents, or other similar products is extremely helpful.
   
   Treatment: The treatment of allergic contact dermatitis focuses primarily on avoiding the substance/medication or treating the infection that led to the reaction. Corticosteroids may be used either systemically or topically to relieve immediate itching and discomfort.
   

Introduction: Autoimmune skin diseases (also known as immune-mediated disorders) are best described as conditions where the body’s immune system is directly responsible for damage done to the skin. Allergic skin disease is also traced to the immune system but is a result of a more indirect reaction. Allergies result from an exaggerated response to a foreign substance (allergen) that the immune system perceives as a threat to the body. Autoimmune skin disease is a result of direct attack by the immune system on the skin itself. When compared to skin disease as a whole, autoimmune disorders are much less common than either infectious or allergic skin disease.

1. Pemphigus Complex: There are 3 main varieties of pemphigus reported in cats: pemphigus foliaceous, pemphigus erythematosus, and pemphigus vulgaris.
   1. Pemphigus foliaceous is the most common form of the pemphigus complex seen in cats. Pemphigus foliaceous primarily affects the face, feet, ears, and nipples. Normal dark coloration of the nose may lose pigment and change to a lighter color. This may result in "photodermatitis." Photodermatitis is a term which implies a skin disorder that worsens with exposure to sunlight.
      
      
   2. Pemphigus erythematosus is usually thought of as a form of pemphigus foliaceous that is confined to the face and ears. Like pemphigus foliaceous, loss of pigment in the nose and resulting photodermatitis may occur.
      
      
   3. Pemphigus vulgaris is extremely uncommon. This is fortunate, because it carries the poorest prognosis of the pemphigus complex disorders. Many cases of pemphigus vulgaris are unmanageable or manageable for only a short period of time. Frequently, euthanasia is the ultimate outcome. This condition does not seem to be associated with any age, sex, or breed types. The feet, face, mouth, armpit (axilla), groin (inguinal area), anus, vulva, and prepuce may be affected. Many cases develop ulcers and inflammation in the mouth, leading to difficulty eating and bad breath.
      
      
   Clinical Signs: The clinical signs for pemphigus complex diseases vary depending on the type of pemphigus the animal has developed. These differences have been described to some extent in the preceding information. In general, the affected areas are covered with pustules, crusts, and/or ulcerations of the skin. Drainage of a clear to yellow/brown discharge and cracks in the affected skin, deep enough to allow bleeding, are common. Secondary infections are frequently seen. Itching (pruritus) is also extremely common with all forms of pemphigus. Sometimes, a coming and going progression of the disease is noted. This can be accompanied by the sudden (hours to days) appearance of new pustules in previously unaffected areas. This is followed by days to weeks of crust formation over the previously affected areas.
   
   Diagnosis: Diagnosing pemphigus complex autoimmune diseases is generally made by a skin biopsy and histopathology. History and physical examination provide extremely important information that is necessary in helping to establish a diagnosis. Feline leukemia (FeLV) and feline immunodeficiency virus (FIV) testing should also be performed in any cat with a suspect autoimmune skin disease. Direct smears with special stains of the crusts and skin discharge may also provide useful information in arriving at a diagnosis of pemphigus foliaceous. Finally, there are special tests that may be run by a laboratory specializing in skin samples. These tests include immunofluorescence and immunohistochemical testing, and can confirm a suspected diagnosis of pemphigus complex disorder.
   
   Treatment/Management: Treatment and management of the pemphigus complex diseases are based on suppressing the immune system’s attack on the skin. In doing so, it is important to establish a specific diagnosis of the type of pemphigus. This is critical because the different pemphigus disorders have different management techniques and vary on their response to treatment. Pemphigus vulgaris, for example, is difficult to manage and is often fatal, while pemphigus foliaceous is less severe but may be fatal without treatment. Pemphigus erythematosus is much easier to manage and carries a good prognosis with treatment.
   
   Therapy is usually initiated with large doses of corticosteroids (prednisolone) to induce remission of disease. After a favorable response, the dosage may be decreased. Many cases may be managed on corticosteroids alone.
   
   In cases where management with corticosteroids alone is incomplete or inappropriate, other drugs that suppress the immune system may be used. Aurothioglucose or chlorambucil may be added to the corticosteroid treatment. Because it can quickly lead to a fatal blood condition, azathioprine, commonly used in dogs with resistant pemphigus disease, should be used with extreme caution or not at all in cats. Doses of immunosuppressive drugs needed to manage pemphigus complex diseases are usually high, and it is important to consider the problems associated with these treatments. Most animals will experience side effects, including a weakened immune system, and may be more susceptible to infections. Boarding, grooming, cat shows, or any other circumstance where the treated cat will be exposed to other cats may need to be off-limits to help prevent spreading of infections. Even exposure to a common upper respiratory virus in an animal with a drug-induced weakened immune system may prove to be very serious. It has been shown that exposure to sunlight tends to worsen many cases of pemphigus complex, and the use of sunscreen lotion on affected areas or avoiding the sunlight altogether may help with therapy and management of these disorders.
   
   
2. Lupus Diseases:
   
   Introduction: Lupus erythematosus is a group of autoimmune diseases where lymphocytes attack the body’s own tissues. Lymphocytes are a type of white blood cell that normally help fight infection. Lymphocytes come in a variety of types, each with a specific function in the immune system. In lupus diseases, different lines of these lymphocytes attack the body’s own tissues and produce disease. Lupus diseases are relatively uncommon, with two major types occurring in the cat.
   1. Systemic Lupus Erythematosus (SLE): This is a rare illness where the lymphocytes attack a wide variety of tissues. Because of the variety of tissues that may be attacked, the clinical signs associated with this illness are also extremely varied and seem to mimic a number of other diseases. SLE has been called "The Great Imitator" due to this variety of signs/symptoms and the tendency to mimic other disorders. Among the tissues that may be attacked is the skin. About 20% of cats with SLE have skin involvement. SLE may produce hair loss, scale ("dandruff"), skin redness, itching, ulcerations, vesicle (blister) formation, overgrowth of the footpads, and persistent secondary bacterial infections of the skin. Any combination of these may be noted in small areas of the skin or may affect the entire body. The face, ears, and paws seem most likely to be affected in cats.
      
      Diagnosis: Diagnosing SLE is extremely difficult. There is no single test that can specifically diagnose SLE. Tests that may be helpful in establishing a diagnosis include bloodwork (CBC, serum chemistry profile), FeLV and FIV screening, and urine analysis. A test called ANA (anti-nuclear antibody) testing can also be used in the diagnosis of SLE; however, this test seems to be somewhat unreliable in cats. This test looks for immune system activity against certain portions of the body’s own cells. Joint taps (if arthritis is present) and skin biopsies (if skin disease is present) are also beneficial.
      
      Treatment/Prognosis: Treating SLE is based on the body systems affected. Generally, drugs that suppress the immune system are the key in managing this disease. Corticosteroids, gold salts, and chlorambucil are the main drugs that are used in treating feline SLE. Antibiotics for secondary infections are commonly used. The prognosis is guarded because many cases develop organ failure (i.e. kidney failure, liver failure) or blood disorders.
      
      
   2. Discoid Lupus Erythematosus (DLE): This is a more benign cousin of systemic lupus erythematosus. In DLE, lymphocytes attack the nose and occasionally regions around the eyes, ears, lips, and chin.
      
      Clinical Signs: A history of crusting in the described areas (nose, eyes, ears, lips, and chin) is the most common clinical sign. Some cats may experience pruritus (itching), with secondary self-inflicted damage to the face.
      
      Diagnosis: Diagnosing DLE is based on history, clinical signs, physical examination, and skin biopsy. A biopsy is necessary for a positive diagnosis and is generally very well tolerated with a quick recovery.
      
      Treatment/Prognosis: Therapy differs according to the severity of an individual case. Minor cases may benefit greatly by reduced exposure to sunlight and/or the use of topical treatments such as corticosteroids and dimethyl sulfoxide (DMSO). DMSO fights inflammation and is available in a gel form. Moderate to severe cases may require more aggressive therapy. Corticosteroids are usually considered the therapy of choice in treating feline DLE.
      
      
3. Erythema Multiforme:
   
   Introduction/Causative Agents: Erythema multiforme is an uncommon autoimmune illness of the skin that affects cats. It is thought that this condition represents a sudden attack by the immune system on skin tissue that is brought on by certain triggers. The most common triggers thought to lead to erythema multiforme in the cat are drug reactions. A variety of drugs have been associated with this problem, including penicillin and gold salts.
   
   Clinical Signs: Erythema multiforme begins with symmetrical red patterns that may progress to blister-like areas and eventually to tissue death and sloughing.
   
   Diagnosis: Diagnosing this disease is based on history, physical examination, clinical signs, and skin biopsy.
   
   Treatment: Treatment of erythema multiforme focuses on correcting any underlying cause. If the underlying cause is removed, the condition itself usually resolves within a few weeks without any specific treatment. Severe cases have been treated successfully with drugs that suppress the immune system (corticosteroids).
   

Introduction: Skin tumors and cancers are seen quite often in cats, and the list of tumor types and cancers is long. Some grow slowly as single or solitary lumps and do not tend to spread beyond the immediate tumor area. Others may grow quickly, involve large or multiple areas of the skin, and may spread to internal organs causing a life-threatening situation. Tumors can be benign (less invasive, less destructive) or malignant (invasive, destructive, and may spread).

1. Basal Cell Carcinomas:
   
   Introduction: Basal cell tumors, both benign and malignant, are the most common type of skin tumor seen in cats. 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 cats.
   
   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 dark 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.
   
   
2. 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. SCC is not found more commonly in certain breeds; however, white cats develop this type of cancer much more frequently than do cats of other colorations. The average age of diagnosis in cats is 9 years.
   
   Clinical Signs: The most common areas for development of SCC in cats are the nose, the tips of the ears, the eyelids, and the lips. SCC also occurs frequently inside the mouth of cats. SCC may either cause ulceration and loss of tissue, or it may be an actual growth on the affected area. Both forms cause inflammation and pain in the immediate area.
   
   Diagnosis/Treatment: Biopsy and histopathology are necessary for a diagnosis. Treatment of SCC may include surgical removal of the cancer, cryotherapy, hyperthermia, or radiation therapy. Amputation of the affected portion of the nose ("nosectomy") or ears is usually required in nasal or aural SCC. The cosmetic result is often surprisingly acceptable. Laser surgery is helping surgeons perform these difficult surgeries, with a more rapid recovery period for the cat. Radiation therapy may be helpful in many cases of feline SCC. In all cases, it is important to avoid additional exposure to sunlight. Generally, this tumor type is extremely aggressive in cats and may spread to local lymph nodes and attack nearby bone, cartilage, muscle, or specialty organs such as the eyes and ears. With aggressive treatment, many cats may live months to even years; however, with advanced tumor growth, the prognosis becomes more guarded.
   
   
3. Mast Cell Tumor:
   
   Introduction: Mast cell tumors (MCTs) are the second or third most common skin tumor in the cat. The average age at diagnosis is 10 years old, although mast cell tumors have been seen in kittens. Male cats and Siamese cats are more commonly affected with mast cell tumors.
   
   Clinical Signs: Mast cell tumors of the skin may appear as distinct lumps or as multiple varying sized lumps in the skin. They occur most commonly on the head and neck of cats. They may be slow or fast-growing. Sometimes, cats may develop so many tumors that it becomes nearly impossible to treat them surgically because of sheer numbers. Mast cell tumors have the potential to spread internally and cause life-threatening disease, although the vast majority of feline MCTs are benign. A syndrome seen in young Siamese cats called histiocytic mast cell tumor syndrome will often regress (return to previous state) on its own.
   
   Diagnosis/Treatment: This is one of the few tumor types that can be diagnosed with a fine needle aspirate and cytology. Treatment depends on the degree of involvement and nature of the cat. Surgery is usually considered the best therapy, if feasible. Other possible treatments include laser surgery, freeze-burning (cryotherapy), and electrotherapy to remove the tumors. Antihistamines may also be used to help control the disease if it spreads internally.
   
   
4. Fibrosarcoma:
   
   Introduction/Clinical Signs: Fibrosarcomas are aggressive, malignant tumors that can occur anywhere on the body. They most commonly occur on the limbs, ears, and trunk in cats. Feline leukemia virus can lead to fibrosarcoma growth in young cats, usually occurring in multiple areas. Some fibrosarcomas have also been found associated with giving certain vaccines. 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. About 20% of fibrosarcomas in cats may spread to other sites in the body.
   
   Diagnosis/Treatment: Diagnosis is accomplished by histopathology. Cytology may help identify the typical spindle-shaped cancer cells that make up fibrosarcomas, but large areas of hemorrhage and tissue death commonly found inside the tumors may yield confusing cytology results. Feline leukemia virus screening should be performed in all cats with fibrosarcoma, especially if there is more than one tumor present. Treatment begins with aggressive surgical removal. Radiation therapy, chemotherapy, and cryotherapy may be helpful in some cases. Based on factors such as location on the body and how much cell division is seen upon microscopic examination, a prognosis can be given. Unfortunately, prognosis is poor in many cases.
   
   Prevention: Avoiding infection with feline leukemia virus is probably the best form of prevention available. Keeping only 1-2 cats per household, retaining cats strictly indoors, and adequate vaccination protection all help in avoiding exposure to FeLV. Unfortunately, the vaccine that protects against FeLV has been known to cause some fibrosarcoma growths. Tumors caused by vaccines are discussed in the next topic.
   
   
5. Postvaccinal Sarcomas:
   
   Introduction/Clinical Signs: Tumors that arise directly as a result of vaccine administration are called postvaccinal sarcomas, vaccinomas, or vaccinosarcomas. The number of cats that develop these potentially devastating tumors following vaccination is on the rise, currently affecting between 1-10 cats per 10,000 vaccinated pets. These tumors develop with more frequency in association with the following:
   1. Feline leukemia vaccines and certain rabies vaccines.
   2. Vaccines that are coupled with adjuvants (carriers such as aluminum, which aid in the function of the vaccine).
   3. Repeatedly giving vaccines in the same spot on the cat.
      
      
   The tumor that results is very large, fast-growing and aggressive. They always occur at the site of vaccination in the cat. The tumors are irregular, firm, and usually attack underlying tissues to the point that they feel continuous with muscle, bone, or other underlying tissues.
   
   Diagnosis/Treatment: Inflammatory lumps that occur following vaccination are very common in both dogs and cats and should go away on their own within 1-3 months. Any lump that remains in a cat beyond this time or is obviously still getting larger after 1 month, should be examined by a veterinarian. Biopsy/removal of the lump should be performed if there is any question as to its nature. Histopathology will diagnose the condition. Most post-vaccinal sarcomas are fibrosarcomas (connective tissue-origin cancer) (see F770). Other types of tumors that may develop following vaccination include liposarcoma (fatty tissue-origin cancer), osteosarcoma (bone-origin cancer), rhabdomyosarcoma (skeletal muscle-origin cancer), and chondrosarcoma (cartilage-origin cancer). The type of tumor that develops depends on what local tissue responded with cancerous growth to the vaccine. Treatment is often difficult. Surgery alone usually is unsuccessful. Radiation therapy is a very helpful treatment tool for post-vaccinal sarcomas and may be combined with very aggressive surgery for the best results. The prognosis usually remains guarded even with the best treatment available.
   
   Prevention: Avoiding vaccines altogether is the best prevention technique available. However, the benefits of choosing to not vaccinate a cat may not outweigh the risks. Any cat that has access to the outdoors and possible exposure to other cats has a far greater risk of being exposed to feline leukemia virus than it would have of developing post-vaccinal sarcoma. Since feline leukemia virus is usually even more devastating and harmful than the sarcoma, the risks of viral infection must be taken into consideration. Some cats in certain situations may be at a low-enough risk to consider foregoing a regular feline leukemia vaccine program— this decision should be made by the owner with the help of a veterinarian. Rabies infection is fairly unlikely in most cats (particularly those kept indoors); however, local law usually mandates that cats be kept updated on rabies vaccine status. A new vaccine by Merial called PureVax offers protection against rabies for cats without the use of an adjuvant and has been shown to minimize vaccine-related reactions.
   
   When giving feline leukemia and feline rabies vaccines, it is recommended that they be given in a limb for the following two reasons: First, if a vaccine-related tumor develops, the sparse tissues on a cat’s limb are less likely to hide the problem, and it may be detected earlier. Secondly, in the event that a tumor does develop, amputation of the limb may actually mean the difference between life and death to the patient. Post-vaccinal sarcomas that develop in the neck or back area do not give the treatment option of amputation and are usually much more difficult to manage.
   
   
6. Lipoma:
   
   Introduction/Clinical Signs: Lipomas or fatty tumors are uncommon in cats. They are benign growths, originating from fat cells (adipocytes).
   
   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 surgeon’s ability to distinguish the tumor from surrounding tissues. This will greatly reduce surgery time and increase the chances of completely removing the tumor.
   
   
7. Sebaceous Gland Tumors:
   
   Introduction/Clinical Signs: Sebaceous glands are found throughout the skin of cats. Tumors of these glands can arise in cats, although they are uncommon. Affected cats are usually older than 10 years of age, and the Persian breed may be predisposed to developing theses tumors. The tumors are usually isolated and occur on the head, neck, and body. They may look like warts, with a pink/white cauliflower appearance.
   
   Diagnosis: There are several types of sebaceous gland tumors, most of which are benign. 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.
   
   
8. Papilloma:
   
   Introduction/Clinical Signs: Papillomas, or warts, are uncommon in cats. There are at least two papillomaviruses that are known to infect cats and cause papillomas to grow. One infects the mouth (especially the tongue), and the other infects the skin. 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).
   
   
9. Melanoma:
   
   Introduction/Clinical Signs: Melanomas are tumors arising from pigmented cells and are usually found as black, gray, or brown growths. In cats, they occur most commonly on the ear, eyelids, lips, head, and neck. Malignant melanomas may spread and cause aggressive destruction to internal organs.
   
   Diagnosis/Treatment: Histopathology is the primary method of diagnosis. Melanomas may occur as benign or malignant growths. Aggressive surgical removal of the tumor is the treatment of choice, although spreading of the tumor may have already occurred at the time of diagnosis. Radiation and chemotherapy have been used with varying success following surgery.
   
   
10. 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, unfortunately, more common cousin of the hemangioma in cats. Hemangiosarcomas appear as blue/black to red plaques, usually less than 2 centimeters in diameter, often with a bruised appearance. Hemangiosarcomas usually occur in older male cats and commonly occur on the head and face (occasionally on the paws). Long term exposure to sunlight may lead to hemangioma and hemangiosarcoma formation in the head and tips of the ears of white cats.
    
    Treatment: Aggressive surgical removal is considered the therapy of choice; however, the prognosis is guarded because spreading of the cancer to other areas in the body can occur. Amputation is usually successful at curing hemangiosarcoma when it occurs in the paws.
    
    
11. Lymphoma:
    
    Introduction: Lymphoma is a malignant cancer of the lymphocytes. (Lymphocytes are cells that help the immune system fight infection.) Any tissue with lymphocytes can be affected, including the skin. There are several classes of lymphoma, including a condition known as "mycosis fungoides." 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 that appears much like immune-mediated skin disease or a skin infection. Although it is misleading because it implies a fungal infection, the name "mycosis fungoides" has never been changed.
    
    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, 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.
    
    Diagnosis/Treatment: The diagnosis of lymphoma is made by biopsy and histopathology of affected areas. Prognosis for cats with lymphoma of the skin is poor and is considered grave for cats 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 lymphoma of the skin, the use of oral retinoids in cats has been tried with occasional 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 cats. Three of the most common endocrine diseases affecting the skin will be discussed: