What is an autoimmune disease?
Our bodies have an immune system that protects us from foreign invaders that can cause disease and infection. However, if you have an autoimmune disease, your immune system attacks itself by mistake, causing serious illness.
The immune cells fail to distinguish the body's normal, healthy cells from foreign cells, and try to destroy the normal tissues. The cause of this "mistake" is not well understood.
Autoimmune disease can affect a single system or multiple body systems. Autoimmune diseases can affect the skin, connective tissue, nerves, muscles, the endocrine system (controls hormones and other chemicals), red blood cells, and the digestive system.
What causes autoimmune disease?
The causes of autoimmune diseases are not understood, although some theorize that genetics and environmental factors, such as allergens or pollutants, play a role. Certain drugs have also been reported as potential triggers for pemphigus foliaceus, a common form of autoimmune skin disease in cats.
Early recognition is extremely important. Left untreated, the complications of autoimmune disease are serious and multiple-system involvement is common. When multiple systems are involved, diagnosis and treatment can be challenging and complicated. Cats with autoimmune diseases should not be vaccinated, except under certain circumstances.
What are some of the common autoimmune skin diseases in cats?
Fortunately, autoimmune skin diseases are rare in cats. Some of the more common forms of autoimmune skin disease include:
Pemphigus complex
Pemphigus is a group of four autoimmune skin diseases. With each disease, the immune system attacks the junctions between skin cells.
Pemphigus foliaceus (PF): This term means "leaf-like pemphigus". PF is the most common autoimmune skin disease in cats. With PF, the patient develops crusts (scabs) and ulcers around the eyes, ears, footpads, groin, and bridge of the nose. In cats, lesions also develop at the toenail beds, creating crusty, sore feet. PF is rarely found in the mouth or at mucocutaneous junctions. It usually appears suddenly, without a recognized cause, but in some cases, it may be drug-induced or can be the result of years of chronic skin disease.
Pemphigus vulgaris (PV): This term means "common pemphigus". It is the most frequent form of pemphigus in humans. Fluid-filled blisters called vesicles form in and around the mouth, eyelids, lips, nostrils, anus, prepuce, or vulva. These vesicles rupture easily, creating painful ulcers. This condition is very rare in cats.
Pemphigus erythematosus (PE): This term means "red and inflamed pemphigus". The most common symptoms are redness, crusting, scales, and hair loss on the nose. Exposure to ultraviolet light worsens this form of pemphigus.
Paraneoplastic pemphigus (PNP): This condition occurs secondary to severe tumors (thymic lymphoma, splenic sarcoma). It is the least common and most severe type of pemphigus.
Bullous pemphigoid
Bullous pemphigoid sounds like a form of pemphigus, but it is a different type of autoimmune skin disease. The immune system attacks the junctions between the epidermis (outer layer) and dermis (inner layer) of skin. Bullae is the medical term for a large, thin-walled sac filled with clear fluid. These sacs form between layers of the skin. Smaller bullae are called vesicles. Usually, the skin is very itchy and large, red welts and hives often appear before or during the formation of bullae and vesicles.
Vesicles and ulcers (ruptured vesicles) may be found in the mouth, at mucocutaneous junctions, and in the armpits and groin. Evaluation of the vesicles is critical to the diagnosis. Because vesicles rupture quickly after formation, the cat must often be hospitalized and examined every two hours until adequate biopsies can be obtained. Bullous pemphigoid resolves spontaneously in many cases. It is considered rare in cats.
Systemic lupus erythematosus
Systemic lupus erythematosus (SLE), commonly referred to as lupus, is a classic example of a multi-systemic autoimmune disease. Lupus is often called the "great imitator", because it can mimic almost any other disease state. The signs of SLE may be acute (sudden onset) or chronic, and they usually wax and wane.
Clinical signs include the following:
- Fluctuating fever that does not respond to antibiotics (common sign)
- Stiffness in the legs or shifting-leg lameness (common sign)
- Blood abnormalities, such as hemolytic anemia (immune destruction of red blood cells)
- Thrombocytopenia (low platelet numbers)
- Leukopenia (a low white blood count)
- Symmetrically inflamed skin, especially over the bridge of the nose (often called a "butterfly lesion")
Discoid lupus erythematosus
Discoid lupus erythematosus (DLE) is another autoimmune skin disease rarely seen in cats. The common clinical signs of DLE include loss of pigmentation around the cat's lips and the skin around the eyes. The ears and the genitals may also be affected. DLE can transform the surface of the nose from its normal "cobblestone" texture to smooth and flat.
Ulcerated sores may occur. Some cats find the disease irritating, while others do not seem affected by it. It is possible that DLE is a non-systemic, less-serious type of systemic lupus erythematosus (SLE). It is considered a relatively benign autoimmune skin disease.
How is autoimmune skin disease diagnosed?
To definitively diagnose autoimmune skin disease, a biopsy of the affected skin is needed. Depending on the location, a skin biopsy may be performed with a local anesthetic. However, if the affected area involves the nose or face, or if the patient is anxious, sedation or general anesthesia may be required. A small, round block of skin is removed with an instrument called a biopsy punch. This tissue sample is then sent to a veterinary pathologist to determine the diagnosis.
How is autoimmune skin disease treated?
The general treatment for autoimmune skin disease is to suppress the immune system (immunosuppression). Your cat will receive drugs to reduce the immune system reaction that is causing the disease. For many cats, treatment with prednisolone or dexamethasone is sufficient. Other cats require stronger immunosuppressive medications such as chlorambucil (Leukeran®) or cyclosporine (Atopica®). If secondary bacterial infections are present, antibiotics and medicated baths or other topical treatments will be used. Your veterinarian will determine the optimal treatment plan for your cat's condition.
What is the prognosis for autoimmune skin disease?
The prognosis for autoimmune skin disease depends on your cat's specific diagnosis and the severity of symptoms. In general, this condition is potentially life-threatening, and requires extensive diagnostic tests and treatments. Autoimmune disease is rarely curable, but is often controllable with appropriate medications.
