We don’t completely understand what causes autoimmune diseases, although genetics are suspected in many types. Vaccinations have also been implemented in some types of autoimmune disease, but a definite link has not been established.
“Autoimmune” essentially means a disease in which the body starts to attack itself. Many diseases fall into this category, and the following 5 are the most common we encounter in veterinary medicine.
Hypothyroidism in Dogs
Like most autoimmune disease, we don’t understand what causes the immune system to revolt and start attacking the patient’s own thyroid, but that appears to be what is happening in this disease. The result is that the dog is left with very little in the way of functioning thyroid tissue, and since the thyroid’s job is to regulate the body’s metabolic rate, the signs of the disease are consistent with that. These dogs often appear “lazy” and lethargic, and gain weight without an increase in food consumption. People often think their dogs look “sad”, but in reality hypothyroid dogs can undergo atrophy of the muscles of the face and head, and consequentially get saggy faces. Hair loss also can accompany the disease.
Diagnosis is fairly straightforward with the right blood test, and patients respond quickly to supplementation with synthetic thyroid hormone. Usually we like to retest these levels on a yearly basis, and make dosage adjustments if necessary.
Immune-Mediated Hemolytic Anemia (IMHA)
IMHA is an often-devastating disease that strikes healthy dogs without warning, typically in middle age. The cocker spaniel is the most commonly affected breed, however any dog can have IMHA. The word “hemolytic” perfectly describes the path of the disease, because it comes from “hemolysis”, which essentially means red blood cells are destroyed, leaving the dog with severe anemia.
In cases of IMHA, red blood cells are incorrectly “tagged” as defective, and the spleen destroys them – kind of like your desktop paper shredder – and removes them from circulation. This happens so rapidly that the bone marrow can’t respond with enough new red blood cells, and the result is a quickly and very severely anemic dog. The most obvious signs of severe anemia are pale gums and extreme weakness and lethargy.
Dogs with IMHA need massive doses of drugs that suppress the immune response to hopefully stop the red blood cell destruction. Sometimes they need a blood transfusion, since anemia leaves them in a critically low oxygen state.
Immune-Mediated Thrombocytopenia (IMT)
IMT is similar to IMHA, except that it’s platelets that are being destroyed. Platelets are integral to your body’s ability to clot once it starts bleeding. Like IMHA, platelets (or thrombocytes) are incorrectly tagged for destruction and removed from circulation, leaving the patient with very low numbers of platelets – a condition known as thrombocytopenia.
Many times dogs with IMT act very normal in the early stages of the disease. But an observant owner will notice bruising on non-haired areas, such as the gums, the insides of the ears, or the skin of the abdomen. The bruising occurs because the lack of platelets is allowing bleeding to occur under the skin.
IMT is treated with the same types of drugs as IMHA, although it typically responds faster, for reasons we don’t quite understand. Allowed to progress without treatment, IMT can lead to severe bleeding into the lungs and chest, and if this occurs the prognosis for recovery is grave.
Allergies in Dogs
Allergies are so common in dogs, and most people can identify with their canine counterparts, since most of us have experienced an allergic reaction ourselves at some point. Where people tend to sneeze and have nasal discharge and itchy eyes, dogs most common get red, inflamed skin that itches intensely, and often have secondary bacterial skin infections as well.
Despite the mountains of research papers that have been written about allergies, we still don’t quite understand what makes one individual’s immune system react so violently to something that most dogs tolerate with no problem. Luckily, most allergic reactions aren’t life threatening, like IMHA and IMT, and we understand quite a bit about treatment. There are many medications, shampoos, special foods, and topical treatments that control the itchiness.
Immune-Mediated Skin and Claw Diseases
Immune-mediated skin diseases are not all that common, but if your dog has a strange lesion on its skin or nails, an immune-mediated cause should be considered. This is especially true if the more common possibilities, such as fleas, mites, and allergies, have been ruled out, or the lesions don’t resolve with appropriate treatment for those diseases.
Immune-mediated conditions seem to favor the face, especially the nose and the bridge of the nose, the tips of the ears, and the feet. Diagnosis usually requires a biopsy of the skin, and treatment depends upon the exact disease. It can take many weeks to see improvement, so owners have to be diligent with medications.