Hypothyroidism in Dogs

The thyroid glands are located in the neck on either side of the trachea (windpipe). These glands require sufficient quantities of iodine for normal production of the thyroid hormone. The thyroid hormone effects the metabolism of all tissues, particularly the metabolic rate. It is required for normal growth and development. The disorders of the thyroid glands are:

Hypothyroidism causes a reduced metabolic rate. Iodine deficiency can lead to cretinism in the young; thickening and swelling of the skin, called myxedema in adults; and goiter, which causes enlargement of the thyroid gland.

The exact cause of hypothyroidism is not always evident or understood. The disease is most commonly seen in four- to six-year-old, medium to large breeds of dogs. Miniature or toy breeds are seldom affected.

Signs of Hypothyroidism

Common signs include lethargy, increased appetite, weight gain, loss of libido, infertility, sensitivity to cold, a brittle, dry, dull coat, loss of hair especially over the neck, back, and tail areas, and in some cases an oily skin and excessive wax in the ears; chronic skin infections. Any dog with chronic skin infections should be tested for hypothyroidism. As the disease advances, the skin darkens in color, thickens, and feels cool to the touch. The dog becomes more dull and irritable, and heart problems may develop. Only about 50% of hypothyroid dogs show the skin and hair changes.

Clinical disturbances associated with hypothyroidism vary among affected animals and not every sign is seen in each animal patient. Many clinical signs associated with hypothyroidism are due to a reduction in basal metabolic rate. A gain in body weight without an associated change in appetite occurs frequently. The weight gain may vary from slight to striking obesity. The animal usually is less active and the owner may observe a reluctance to play or take walks. The inactivity also contributes to the weight gain. Dogs with hypothyroidism may have difficulty in maintaining normal body temperature and are often heat seekers. They will lie on or near sources of heat, such as registers, radiators, and electric blankets, and be reluctant to venture outdoors in cold weather. Excessive shivering may be observed and the skin frequently feels cool.

<== Hypothyroidism - Skin Manifestations

In case of congenital hypothyroidism of Toy Fox Terriers, there is delayed ear and eye opening, palpable goiter (enlarged thyroid gland to compensate for decreased production), stunted growth, mental dullness.

Treatment of Hypothyroidism

Treatment involves the use of replacement thyroid hormone drugs, usually for life. Establishing the dosage requires veterinary supervision and periodic monitoring of the affected dog is absolutely necessary. If the diagnosis is correct, the prognosis is good. Many dogs have increased activiity in 10 days; hair regrows in 4-6 months and other signs improve in 2 months.

CAUTION: Because vegetables such as broccoli and cabbage can depress thyroid hormones if eaten in large amounts, they should not be fed to dogs with hypothyroidism.

References:
1. Thyroid Disorders in Animals. Charles C. Capen
2. Hypothyroiidiism. Dr. Sandy Merchant