Hypothyroidism
Also called: Underactive thyroid, primary hypothyroidism
- Dogs
- Hormonal (endocrine)
- Middle-aged
A deficiency of thyroid hormone — usually from immune-mediated thyroiditis or gland atrophy — that slows the body's metabolism. It is very treatable, but is also, in Merck's words, one of the most over-diagnosed diseases in dogs, so careful testing matters.
Signs to look for
- Lethargy and mental dullness
- Weight gain without eating more
- Cold intolerance or heat-seeking
- Dry coat, excessive shedding, or symmetrical hair thinning
- Recurrent skin or ear infections
How a vet diagnoses it
Clinical suspicion plus laboratory testing — low total T4 and free T4 with elevated TSH support the diagnosis. Your vet will test only when disease is genuinely suspected, because other illnesses and some drugs lower T4, and some breeds (e.g. sighthounds) naturally run lower.
Treatment
Lifelong thyroid-hormone replacement (levothyroxine/thyroxine), with periodic monitoring and dose adjustment.
Monitoring at home
Thyroid levels and clinical signs; most signs resolve over a few months. Prognosis is excellent with treatment.
Who tends to get it
Most common around 4–10 years of age, in mid- to large-size breeds (e.g. Golden Retriever, Doberman, Irish Setter); rare in toy breeds. Both sexes.
This library is educational reference only. It is designed to help you learn about health conditions your pet may have been diagnosed with — it does not interpret your pet's symptoms, cannot diagnose, and is not a substitute for veterinary care. Cats and dogs often hide illness well, so signs can be subtle. Any new, persistent, or worsening sign warrants a vet visit.