This case report discusses a rare instance of diet-associated iodine-deficiency goitrous hypothyroidism in a 9-year-old spayed female Chihuahua. The dog was fed a non-standardized home-prepared diet lacking vitamin and mineral supplementation. Initially, the dog exhibited mild weight gain and bilaterally enlarged thyroid lobes but did not show the typical symptoms of hypothyroidism.
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Laboratory tests indicated significantly reduced concentrations of total and free thyroxine, alongside elevated thyroid-stimulating hormone (TSH) levels, confirming primary hypothyroidism. Ultrasonographic examination revealed symmetric thyroid enlargement, while fine-needle aspiration ruled out neoplasia. Serum inorganic iodine levels were severely low, prompting a dietary change to a commercially prepared, iodine-supplemented diet without initiating thyroid hormone replacement.
Within two months, the dog's thyroid hormone levels normalized, iodine concentrations returned to baseline, and ultrasonography showed a dramatic reduction in thyroid size. These findings highlight the significance of adequate dietary iodine and the potential reversibility of thyroid function following appropriate dietary changes.
Despite hypothyroidism, the dog displayed few overt clinical symptoms. The underlying mechanism may include the body's ability to preferentially produce T3 over T4 during iodine deficiency, thus conserving iodine while maintaining metabolic function.
This case underscores the importance of nutritional assessment in canine patients, particularly those on home-prepared diets, and emphasizes the need for awareness of nutrient deficiencies such as iodine in veterinary practice.