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The Difference Between Hypothyroidism and Hyperthyroidism in Dogs

The thyroid gland, located in the throat beneath the larynx, produces hormones that regulate metabolism and otherwise assist with a variety of biological processes. Dogs with hypothyroidism produce too little thyroid hormone, which results in a slow metabolism and other complications. Dogs with hyperthyroidism produce too much thyroid hormone, causing an accelerated metabolism and related symptoms.

Hypothyroidism in Dogs

Hypothyroidism most commonly occurs in dogs with thyroiditis, an autoimmune condition that causes the breakdown of thyroid tissue. All dogs are susceptible, but onset typically occurs during middle age in large and medium-sized breeds.

Poor coat growth and skin changes that affect both sides of the body are often seen in dogs with hypothyroidism. Hair loss on the throat, chest, rear of the thighs, sides of the torso, or top of the tail is a standard clinical sign. Skin in these affected areas is typically darker, dry, and thickened or swollen.

A slowed metabolism causes weight gain, reduced ability to regulate body temperature, lethargy, depressed heart rate, loss of heat cycles, or other various symptoms. Mood or behavioral changes, high cholesterol, and numerous secondary disorders are also possible with production of too little thyroid hormone.

Your veterinarian can diagnose hypothyroidism with a blood test. The condition is generally permanent but is manageable with medication. The primary course of treatment is administration of supplemental thyroid hormone. Symptoms should correct with treatment, which also requires close monitoring, frequent examinations, and periodic blood tests.

Hyperthyroidism in Dogs

Canine hyperthyroidism is rare and typically associated with benign or malignant thyroid tumors. It is also sometimes seen as a side effect of certain medications. The related acceleration in metabolism can have many effects on various organ systems. Increased appetite and weight loss are hallmarks of the condition, and increased thirst and urination are also common.

Other symptoms associated with an excess of thyroid hormone include a chronically disheveled coat, poor physique, diarrhea, vomiting, rapid or labored breathing, increased heart rate or murmurs, and hyperactivity. Also, the thyroid gland is usually enlarged; it may be detectable as a lump in the throat.

Your veterinarian can identify hyperthyroidism as the likely cause of symptoms by checking for thyroid enlargement with a physical examination or imaging. Blood tests and urinalysis confirm the diagnosis. False negatives are somewhat common, though, especially early on in the course of the disease. When hyperthyroidism is probable but not confirmed, repeat visits and tests are necessary.

If overproduction of thyroid hormone is a result of a specific medication, an alternative therapy or dose adjustment is generally sufficient to solve the problem. In other cases, drugs can effectively decrease thyroid hormone output. In the event a tumor is to blame, removal (and often follow-up radiation treatments) sometimes cures the associated hyperthyroidism. Treatment with radioactive iodine and surgical removal of the thyroid are other options for some dogs.

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{ 1 comment… add one }
  • Ashe April 3, 2014, 6:02 pm

    Thanks for the terrific summary of the differences between Hypo and Hyperthyroidism.

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