Spontaneous adult-onset hypothyroidism in a cat

Spontaneous adult-onset hypothyroidism, confirmed by a thyroid-stimulating hormone stimulation test, thyroid biopsy, and response to replacement therapy, is described in a female cat. Clinical signs consisted of profound apathy, hypothermia, poor hair growth, severe seborrhea sicca, and a puffy face. Cutaneous histological changes consisted of epidermal and follicular hyperkeratosis, teloginization of hairs, and dermal mucin deposition. There was no adnexal atrophy. Lymphocytic thyroiditis, equivalent to Hashimoto's thyroiditis, was shown by thyroid biopsy. Clinical signs rapidly responded to thyroxine replacement therapy. Glucose intolerance was coexistent with the hypothyroidism, but was not dramatically influenced by thyroxine therapy and probably was an independently occurring endocrinopathy.