Radiation-Induced Painless Thyrotoxic Thyroiditis Followed by Hypothyroidism: A Case Report and Literature Review

A 68-year-old woman presented with a small painless goiter and thyrotoxic symptoms immediately after 50-Gy external radiation for mucoepidermoid carcinoma of the submandibular gland. Elevated serum thyroid hormone and thyroglobulin levels, and undetectable serum thyrotropin level, together with extremely low thyroidal radioiodine uptake established the diagnosis of painless thyrotoxic thyroiditis. Thyroidal autoantibodies were negative. At follow-up without medication, all the symptoms disappeared, and laboratory abnormalities normalized within 6 months. One year later, the patient developed compensated hypothyroidism as indicated by elevated serum thyrotropin level with low normal serum thyroid hormone levels.