Canine hypothyroidism
Dogs onlyKey concepts ·Also called: underactive thyroid dog, hypothyroid dog, thyroid deficiency
What it is
Hypothyroidism slows the metabolism throughout the body. Diagnosis is rarely made on a single test: a low total T4 is common in any ill dog, so free T4 and TSH are added, and a raised cholesterol is often the supporting clue that tips the balance.
Why it matters
It is one of the more over-diagnosed conditions in dogs, because so many unrelated illnesses and medications lower T4. Getting it right matters in both directions — an untreated hypothyroid dog stays flat and overweight, while a misdiagnosed dog takes a lifelong medication it does not need and the real problem goes unfound.
What it can point to
- Weight gain without an increase in food, lethargy, and heat-seeking behaviour
- A dull, thinning coat, hair loss along the flanks and tail, and recurrent skin or ear infections
- A low total T4 with a raised TSH — the most convincing laboratory combination
- A raised cholesterol, present in the majority of affected dogs
- A mild non-regenerative anaemia
Dogs and cats differ
Naturally occurring hypothyroidism is a dog disease; cats develop it almost only after treatment for hyperthyroidism. Among dogs, breed predisposition is real — Dobermanns, Golden Retrievers, Boxers and several others are over-represented — while sighthounds simply run low T4 in normal health and are easy to misdiagnose.
Questions worth asking your vet
- Could another illness or medication be lowering the T4 rather than a thyroid problem?
- Do the TSH and free T4 support the diagnosis?
- If we treat, how soon should we recheck and what improvement should I expect?
Related terms
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