Beneath your dog's fur coat is a network of antibodies, white blood cells and other substances that work together to recognize and fight off foreign invaders. When functioning properly, the immune system differentiates between foreign cells and its own cells. Occasionally, a dog's immune system isn't able to recognize the differences between the cells and attacks and rejects the dog's bodily tissue as foreign. Some immune diseases in dogs are inherited, while others can be caused by viruses, illness or medication.
Autoimmune Hemolytic Anemia
A dog's red blood cells may be tagged as foreign by the immune system if they're carrying antibodies or affected by drugs, infections, parasites or disease such as cancer. Usually, it's business as usual when damaged red blood cells are destroyed. However, sometimes the red blood cells are destroyed faster than they can be replaced, causing autoimmune hemolytic anemia. Weakness, loss of appetite, lethargy and increased heart rate are often initial signs; jaundiced eyes, skin and gums are seen as the condition progresses. Corticosteroids usually are administered, and other drugs, known as chemotherapeutics, occasionally are necessary. When a dog doesn't respond to treatment, the vet may recommend a surgical removal of the spleen, taking away the primary means for the red blood cells' destruction. Autoimmune hemolytic anemia has a guarded prognosis.
When the clotting cells, otherwise known as thrombocytes, are destroyed, the dog has immune-mediated thrombocytopenia. The mechanism is the same as autoimmune hemolytic anemia. Symptoms include blood in the urine and feces, bruising and excessive bleeding during surgery, trauma or heat cycle. Treatment includes corticosteroids and other medications as necessary, as well as a splenectomy if the dog doesn't respond to medication. This condition has a generally favorable prognosis.
Autoimmune diseases of the skin are uncommon in dogs, however occasionally a dog may experience one of the four diseases of the pemphigus complex, an autoimmune skin disorder marked by blisters and ulcers.
- Pemphigus foliaceus mainly affects the head, ears and footpads, eventually spreading elsewhere on the body. Symptoms include itchy, red skin, shallow ulcers, scales, pustules, crusts and fluid-filled sacs in the skin, as well as lethargy, swelling and swollen lymph nodes.
- Pemphigus erythematosus is similar, often with loss of color in the lips.
- Pemphigus vegetans primarily presents large patches of oozing lesions.
- Pemphigus vulgaris is the most serious type and shows more severe symptoms of pemphigus foliaceus and erythematosus. Ulcers may be shallow or deep and the dog's lips, gums, underarms and groin areas may be affected. Fever, depression and secondary bacterial infections are normal.
Medication, including steroids, limiting the dog's exposure to the sun and regular veterinary checkups typically are used to manage pemphigus.
Systemic Autoimmune Disease
Systemic lupus erythematosus usually is referred to simply as lupus, and occurs when a dog's body is attacking its own healthy tissue as though it's damaged and needs to be destroyed. There are several types of lupus.
- Skin/exocrine lupus presents in skin lesions, ulcers, hair loss, loss of pigmentation and scaling.
- Musculoskeletal lupus affects the soft tissue within the joints, resulting in swollen, painful joints, muscle pain and wasting and lameness.
- Blood, lymph and immune system lupus will cause the lymph nodes to swell.
- Renal/urologic lupus causes kidney and liver enlargement.
Other symptoms associated with lupus include fever, lethargy and appetite loss. Treating lupus depends on what part of the body is affected and often can be accomplished at home. Cage rest may help a dog with joint pain and immunosuppressive drugs may help depress his immune system's response. Corticosteroids are helpful to reduce inflammation in the lymph nodes. Regular veterinary visits are necessary to monitor for side effects and treatment effectiveness. The prognosis for lupus is guarded, particularly for dogs with kidney disease.