Goitre in a dog on a home-made diet: thyroid ultrasound
Adult dog fed a home-made meat-and-rice diet without mineral supplement for over a year. It is lethargic and gaining weight, and bilateral swelling can be felt in the neck. Total T4 is low and TSH is high. Transverse neck ultrasound at the level of the trachea:
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What is the most likely explanation for these findings?
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A. Bilateral thyroid carcinoma; thyroidectomy is indicated
Canine thyroid carcinoma is usually unilateral, heterogeneous and highly vascular, and rarely causes hypothyroidism. Here both lobes are symmetrically enlarged, homogeneous and smooth-margined.
B. Goitre from dietary iodine deficiency; correct the ration
Correct. Bilateral, symmetric, homogeneous lobe enlargement with low T4 and high TSH in a dog on a home-made diet without mineral supplement suggests iodine-deficiency goitre: high TSH drives thyroid hyperplasia. Once the diet is corrected, the lobes usually shrink within weeks and function normalises.
C. Lymphocytic thyroiditis, which enlarges both thyroid lobes
Lymphocytic thyroiditis is the most common cause of canine hypothyroidism, but it leads to small, hypoechoic, irregular lobes through destruction and atrophy, not to symmetric enlargement.
D. Hyperthyroidism from thyroid tissue in a raw diet
Raw diets containing thyroid tissue cause hyperthyroidism with high T4 and suppressed TSH. This dog has the opposite profile: low T4 and high TSH.
lightbulb Key takeaway
Home-made diets without a properly formulated mineral supplement can be iodine-deficient. With hypothyroidism and enlarged, homogeneous thyroid lobes, review the diet before starting levothyroxine; follow-up ultrasound shows the lobes shrinking once it is corrected.
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Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.