- Primary hypothyroidism results from thyroid tissue damage. The damage may be due to inflammation (often cause by autoimmune problems), tumors or degeneration, according to Vetinfo. Over 90 percent of dogs with hypothyroidism have the primary form. Other causes include brain or pituitary problems, medications, thyroid removal and radiation of thyroid tumors. Iodine deficiency, particularly in some breeds such as giant schnauzers and boxers, may cause hypothyroidism.
- Hypothyroid symptoms include lethargy, anemia, weight gain, slow heart rate and intolerance of the cold, according to Vetinfo. High cholesterol due to hypothyroidism may cause deposits on the eyes, which may grow large enough to rupture, resulting in ulcers on the eye, according to Brooks. The most common symptoms of hypothyroidism are coat and skin problems, including hair loss, darkened skin, skin infections, brittle or dry coat and thickened skin, particularly on the face and head. Untreated, hypothyroidism can cause heart problems and blindness, according to Vetinfo.
- Hypothyroidism generally begins in middle age or older dogs. Some breeds, such as German shepherds and toy fox terriers, may have a genetic form of hypothyroidism that develops at a younger age. Other breeds with an increased rate of hypothyroidism include golden retrievers, Irish setters, Rottweilers, Doberman pinschers, Great Danes, dachshunds, boxers, English setters, Shetland sheepdogs, Tibetan terriers and German wirehaired pointers. Dogs with dwarfism are at a higher risk of developing hypothyroidism.
- Blood testing can help determine if a dog has hypothyroidism. Testing for hypothyroidism has complicated factors, including breed differences, medication interaction and result variations among dogs with hypothyroidism, according to Brooks. Your veterinarian may prescribe medication for hypothyroidism without a positive test result. If your dog's symptoms improve, a diagnosis of hypothyroidism is probable.
- Treatment for hypothyroidism is generally oral hormone replacement using a synthetic form of L-thyroxine. According to the University of Georgia, results generally begin within two weeks. Skin improvements may take up to eight weeks, according to Texas A&M University. Your veterinarian may retest after one to two months and then every six months or if symptoms return. Treatment is for life, but the prognosis is good for most dogs. According to the University of Georgia, the best prognosis for early on-set genetic hypothyroidism depends on early treatment.