Autoimmune Disorders in Pets
These disorders are caused by a defect in a pet’s immune system. When it is working correctly, the immune system is a protective defense for the body against infections and foreign proteins. However, with immune mediated skin disease, the body’s immune system recognizes a component of the skin as foreign, resulting in skin lesions.
Download our handout on Pemphigus Foliaceus.
Pemphigus foliaceus (PF) is a non-contagious autoimmune skin disease that affects dogs, cats, horses, and people. The problem starts when the animal’s body recognizes the skin as “foreign” and the immune system attacks it. Short-lived blisters or fluid-filled pimples develop, and as these rupture, crusts and hair loss occurs.
In most cases, it is unknown what causes this problem. In some cases, we might suspect drugs, viruses, genetics, or environmental influences, but these can be difficult to prove. Males and females alike are affected. The age of disease onset is variable and can occur from under 1 year old to over 10 years old. In older dogs, we may suspect cancer as a problem that sets off PF.
PF has to be definitively diagnosed before starting treatment because several other diseases may mimic it. We will perform various tests including skin scrapings, cytology, cultures for bacteria or fungi, and therapeutic trials for parasites to rule out other differentials. A skin biopsy must be done to confirm a diagnosis of PF. Biopsies are taken by surgically removing a small piece of the affected skin, specially preparing it, and sending it to a laboratory where the skin is looked at under a microscope by a dermatopathologist. Diagnosis may be difficult and occasionally several biopsies need to be taken at various times to diagnose PF.
The immune-suppressing drugs used to treat this disorder stop the immune system from attacking the skin, but can have serious side effects. Your pet must be monitored regularly, with the type of monitoring dependent upon the specific drugs used. Treatment is usually life-long and periodic monitoring is required. No tests can determine which drug or drug combination will be best for an individual. Sometimes several different drugs will be tried and may need to be changed if there is inadequate response.
Discoid Lupus Erythematosus (DLE)
Download our handout on DLE.
Discoid lupus erythematosus is a common immune-mediated skin disease of dogs but rarely of cats. The underlying cause that triggers the immune system to react this way is unknown; however, sun exposure and sensitivity to ultraviolet light may irritate the condition. Skin lesions occur primarily on the nose but may appear on the face and legs. Initially you may see a loss of pigment or color, followed by redness, ulcers, and crusts. A secondary skin infection is common with the skin lesions observed with DLE.
A diagnosis of DLE is confirmed by taking skin biopsy samples from the affected areas. Subtle changes can be found in the skin biopsy samples and they are examined by a dermatohistopathologist to obtain the correct diagnosis. Because secondary skin infections are common with DLE, any skin infection should be treated before we perform the biopsies.
DLE is a life-long disease that can be managed with a variety of medications and supplements. Since it is considered to mainly affect the skin, topical therapy may be sufficient to control it. However, if the disease becomes more severe, we may recommend systemic medication that can treat the immune system. Suppression of the immune system is typically not needed in cases of DLE.