Hypothyroidism results when the thyroid gland doesn't make enough of the hormones triiodothyronine and thyroxine. This failure of the thyroid, in many cases, is caused by inflammation of the gland or withering of the thyroid. The dog's immune system malfunctions and starts attacking the gland, which damages the thyroid and causes it to put out fewer essential hormones into the body.
Congenital diseases, iodine deficiency, pituitary tumors and other pituitary gland diseases are often to blame for hypothyroidism in dogs. Middle-aged dogs and older dogs are most susceptible, especially if they are larger. Secondary hypothyroidism, unusual in dogs, is caused by systemic disease and the pituitary gland failing to release the thyroid stimulants TSH, or thyroid-stimulating hormone, and TRH, or thyrotropin-releasing hormone. Tumors in the pituitary or hypothalamus can cause this.
Lethargy is a symptom of hypoactive thyroid, as is mental dullness and muscle weakness. Hair loss following symmetrical patterns is common. An afflicted dog gets cold easily and suffers ear infections as well as coat and skin diseases. Exercise intolerance, weight gain and heat-seeking behavior are common symptoms. Dandruff and seborrhea of the skin are possible. Heart arrhythmia is a sign, as is a slower-than-normal heartbeat. Anemia, seizures and infertility are common symptoms.
The veterinarian examines the dog and determines his condition. He'll measure the hormone levels of the dog's body; if the thyroid hormones are off balance, it's a sure sign of thyroid disorder in the animal. The modified equilibrium dialysis test that measures the thyroxine levels in the dog's blood determines the condition as well as measures the thyroid-stimulating hormone. If the TSH levels are high and the thyroxine levels are low, hypothyroidism is the diagnosis.
If the dog takes pills by mouth easily, oral thyroid hormone replacement therapy is a possibility for the animal. Dogs who dislike taking pills can be given the meds by breaking up the pills and mixing them into his food. Most dogs respond well to treatment in as little as a week's time, displaying improvement in alertness and energy levels. Many of the other symptoms take longer to vanish, but, over time, marked improvements are seen.
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