Hypothyroidism in Dogs
One of the most common endocrine disorders in dogs, usually caused by immune-mediated destruction of the thyroid gland in middle-aged, medium-to-large breed dogs.
Overview
Canine hypothyroidism most commonly results from lymphocytic thyroiditis (immune-mediated) or idiopathic thyroid gland atrophy, leading to insufficient thyroid hormone production.
Clinical signs
- Lethargy and exercise intolerance
- Weight gain without a corresponding increase in appetite
- Cold intolerance
- Symmetric hair loss on the trunk and a dull, dry coat
- Skin hyperpigmentation and, in some dogs, a "tragic" puffy facial expression
Diagnosis
- Total T4 as an initial screening test
- Free T4 by equilibrium dialysis plus endogenous TSH for more reliable confirmation, since illness unrelated to the thyroid can also lower total T4
Treatment
- Daily oral levothyroxine supplementation
- Periodic monitoring of T4 levels, typically drawn a few hours after dosing, to fine-tune the dose
Prognosis
Excellent with appropriate lifelong supplementation. Most clinical signs improve within weeks to a couple of months of starting treatment.
This page is general reference information for educational purposes. It is not a substitute for an individual clinical assessment, current formulary guidance, or the judgment of a licensed veterinarian treating a specific patient.
Frequently asked questions
Is hypothyroidism in dogs treatment lifelong?
Yes, in almost all cases levothyroxine supplementation is needed for the rest of the dog's life, since the underlying thyroid gland damage does not reverse.
Can hypothyroidism cause skin problems?
Yes - a dull, dry coat, symmetric hair loss on the trunk, and darkened or thickened skin are classic signs, and skin/coat changes are often among the first things owners notice.