Definition of Hypothroidism
Hypothyroidism occurs when the thyroid gland doesn’t make enough of two essential hormones, triiodothyronine (T3) and thyroxine (T4). Primary hypothyroidism is the most common form of this disease and usually is caused by inflammation and atrophy of the thyroid gland. For some reason, the dog’s immune system targets and damages its own thyroid tissue as if it were foreign. This decreases the amount of T3 and T4 circulating in the bloodstream, triggering a cascade of metabolic problems. Environmental and dietary factors may also be involved. Secondary hypothyroidism, which is rare in dogs, can be caused by systemic disease, dietary iodine deficiency and space-occupying pituitary gland tumors, among other things. Hypothyroid dogs can have a variety of symptoms, including mental dullness, lethargy, weakness, exercise intolerance, weight gain for no apparent reason, heat-seeking behavior (they get cold easily), symmetrical hair loss without itchiness, ear infections and assorted skin and coat abnormalities. Fortunately, hypothyroidism is fairly easy to diagnose and treat.