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Hypothyroidism in Dogs

The thyroid gland is an essential gland in the body, producing a number of hormones, including T3 (liothyronine) and T4 (levothyroxine), both of which are required for normal metabolism in the body.

Hypothyroidism is a clinical condition resulting from a lowered production and release of T4 and T3 hormones by the thyroid gland. It is common in medium to large-sized dogs, with some being more predisposed than others. These breeds include Doberman pinschers, Irish setters, golden retrievers, great Danes, old English sheepdogs, dachshunds, miniature schnauzers, boxers, poodles, and cocker spaniels. It is also more commonly diagnosed in middle-aged dogs between the ages of 4-10 years. Neutered male dogs and spayed females are found to be at higher risk than intact dogs.

Symptoms and Types

• Lethargy
• Generalized weakness
• Inactivity
• Mental dullness
• Unexplained weight gain
• Hair loss (alopecia)
• Excessive hair shedding
• Poor hair growth
• Dry or lusterless haircoat
• Excessive scaling
• Recurring skin infections
• Intolerance to cold
• Tilting of head to one side (uncommon)
• Seizures (uncommon)
• Infertility (uncommon)

Causes

• Unknown etiology (origin)
• Congenital disease
• Iodine deficiency
• Cancer
• After-effect of medical treatment, including surgery

Diagnosis

Your veterinarian will perform a thorough physical exam on your dog, taking into account the background history of symptoms and possible incidents that might have precipitated this condition. You will need to provide your veterinarian with a thorough history of your dog's health leading up to the onset of symptoms.

Finding the exact cause of hypothyroidism may require a thorough investigation. Routine laboratory testing will include a complete blood count, biochemistry profile, and urinalysis. Your doctor may be able to make an initial diagnosis based on the results of these tests, but endocrine testing is also an important panel for the diagnosis of hypothyroidism. The levels of T3 and T4 will be measured to determine if these are in the lower ranges. Radiographic studies may also be conducted to examine your dog internally for abnormalities that may be causing the dysfunction of the thyroid glands.