If your cat is having skin problems, the usual suspects are external, like fleas, mites, fungus or bacteria. Sometimes the problem, as the saying goes, is more than skin deep. A malfunctioning immune system can cause trouble much more serious than a few flea bites.
When your cat has an autoimmune disease it means that the body is attacking itself. Your cat's immune system doesn't recognize certain normal, healthy cells and begins destroying them. In cats, autoimmune diseases that affect the skin directly are fairly rare, but other autoimmune disorders that are directed at internal organs can also cause skin problems.
Pemphigus is the most common autoimmune skin disease found in cats. This disease is divided into three types, depending on where it attacks the skin, but in each case the bond between the layers of skin is the victim of the attacking immune system. As the bond is eroded, blisters and sores show up on the skin and break open. If your cat has pemphigus, she will have pustules, scaly patches, sores and hair loss. She is also likely to be itchy and uncomfortable and may run a fever or act lethargic. Bacterial skin infections are also commonly seen with pemphigus. This disease can be fatal if it is not treated.
There are different types of lupus. One affects your cat's skin directly, and the other affects it indirectly. Discoid lupus erythematosus is a big name for the form of lupus that affects the skin. Symptoms are often seen on the nose at first, in the form of lesions, open sores and loss of pigmentation. Although it can appear on any part of the skin, it commonly shows up where the skin is thin and sensitive, such as near the mouth, anus, eyelids and ears. Systemic lupus erythematosus attacks your cat's organs, in turn causing skin problems. Hair loss is common, as well as sores and lesions similar to those caused by the discoid form of lupus.
Bullous pemphigoid sounds similar to pemphigus, but it is a different autoimmune disease that affects the skin. Large fluid-filled sacs, similar to blisters, form under the skin and cause itching, welts and hives. Ulcers are also often found in and around the mouth and in places where the skin folds, such as "armpits" and the groin. The fluid sacs burst quickly, making it difficult for your veterinarian to conduct a biopsy.
Suppressing the immune system so it will stop attacking the skin is the main type of treatment for these diseases. Steroids might be prescribed temporarily or as a permanent treatment. Obviously, the problem with suppressing the immune system is that your cat becomes more vulnerable to all other types of infection and illness. Frequent blood tests and check-ups are important. Antibiotics and topical skin treatments might also be needed to clear up remaining skin problems.