Anaplastic thyroid carcinoma with thyrotoxicosis and hypoparathyroidism.

OBJECTIVE: To describe a patient who presented with anaplastic thyroid carcinoma and thyrotoxicosis in whom hypoparathyroidism developed.
METHODS: We present the clinical and laboratory findings in a patient with anaplastic thyroid carcinoma and thyrotoxicosis. We also review the literature for previous cases of anaplastic thyroid carcinoma with thyrotoxicosis.
RESULTS: A 74-year-old man presented with left-sided neck pain and a rapidly enlarging neck mass. Initial thyroid function tests revealed the following: thyrotropin (thyroid-stimulating hormone or TSH) 0.03 microIU/mL, free thyroxine 1.28 ng/dL, and total triiodothyronine 119 ng/dL. A thyroid radioiodine uptake scan was 2.2% at 25 hours. Pathology examination of the neck mass disclosed anaplastic thyroid carcinoma. His thyrotoxicosis was managed with beta-adrenergic blockade. The thyroid carcinoma was treated palliatively with external beam irradiation. During week 9 after the patient's initial presentation, symptomatic hypocalcemia developed, with an ionized serum calcium level of 0.75 mmol/L (normal range, 1.15 to 1.29) and a parathyroid hormone level of 21.2 pg/mL (normal range, 10 to 65). He was given calcium gluconate intravenously for initial management, followed by orally administered calcium carbonate and calcitriol. At week 15, he died of complications attributable to anaplastic thyroid carcinoma.
CONCLUSION: Thyrotoxicosis due to thyroiditis is a rare initial manifestation of anaplastic thyroid carcinoma. Hypoparathyroidism due to anaplastic thyroid carcinoma has not been reported previously.