Rapid thyrotoxicosis in anaplastic thyroid carcinoma.

We present the case of a 71-year-old man with anaplastic thyroid cancer. On presentation, his thyroid function was normal, but he subsequently developed sudden, rapid thyrotoxicosis. Thyrotoxicosis in anaplastic thyroid carcinoma is very rare, but in all previously reported cases the patient was thyrotoxic at presentation. Our case is unusual as our patient presented euthyroid, and thyrotoxicosis developed subsequently. We challenge current ideas regarding the biochemical pathophysiology of rapid thyrotoxicosis in anaplastic thyroid carcinoma and provide an alternative explanation.