Hypothyroidism

Hypothyroidism

Species: Dog

Breeds Affected: All Breeds (medium to large breeds, typically 4–10 years old, are most commonly affected; e.g. Golden Retrievers, Doberman Pinschers, Boxers)

Hypothyroidism is a hormonal disorder where the thyroid gland fails to produce enough thyroid hormone. In dogs, this is usually due to immune-mediated thyroiditis or thyroid gland atrophy. The result is a slowing of metabolism. It is one of the most common endocrine disorders in middle-aged dogs. Hypothyroidism is not life-threatening, but it causes significant quality-of-life issues if untreated.

• Because thyroid hormone affects all organ systems
• signs can be widespread. Classic symptoms are lethargy and mental dullness
• weight gain despite normal diet
• and exercise intolerance. Dogs often can’t tolerate cold and seek warm places (cold intolerance). Skin and coat changes are common: the coat becomes dull
• thin
• with symmetrical hair loss (often over the trunk and tail – a “rat tail” appearance). Skin may become hyperpigmented and susceptible to infections (recurrent skin and ear infections are frequent due to low thyroid hormone). High cholesterol levels are a laboratory hallmark and can sometimes lead to fatty deposits in the eye. Rarely
• severe cases show nerve dysfunction (weakness
• head tilt).

Hypothyroidism is highly treatable with daily thyroid hormone replacement. Dogs are started on an oral levothyroxine (synthetic thyroid hormone) dose, and the dose is adjusted based on blood tests. This medication must be given for life. Most symptoms improve within a few weeks to months of therapy – the dog becomes more active, and skin and coat gradually recover. No special diet is usually required, but weight loss through portion control may be needed for obese hypothyroid dogs. Regular monitoring of thyroid levels and clinical signs is necessary, especially in the first few months of treatment, to ensure proper dosing.

Levothyroxine (T4 thyroid hormone) is the standard medication – brands like Thyro-Tabs® are commonly used. It is given by mouth, usually twice daily, to normalize the dog's thyroid hormone levels. After starting therapy, blood tests for T4 are done to confirm the dose is adequate, and then typically every 6-12 months thereafter. Levothyroxine is very safe and effective; side effects are rare unless the dose is too high (which would cause signs of hyperthyroidism like restlessness or weight loss). Other medications are generally not needed once the correct levothyroxine dose is established, as this treatment fully replaces the deficient hormone.