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Hyperthyroidism: A rare late toxicity of cancer radiotherapy

INTRODUCTION: Radiotherapy of childhood cancers, despite technical progress, remains delicate because of the fear of long-term toxicities, especially dysthyroidism. We report a case of hyperthyroidism, which occurred four years after irradiation for cavum cancer. OBSERVATION: A 20-years-old girl with a history of cavum cancer at the age of 16 years was treated with induction chemotherapy followed by radiotherapy with a dose of 70 Gy to the cavum and 50 Gy to the cervical and supraclavicular lymph nodes. The thyroid received 24 Gy to the lobes and 16 Gy to the isthmus. The tumor response was complete and stable. Four years after the radiotherapy, signs of irritability, rebellion towards her mother, attributed to late adolescence, thermophobia and weight loss appeared. On clinical examination, a small exophthalmos associated with a goiter predominantly on the left was noted. The thyroid workup confirmed hyperthyroidism: free T4 concentration higher than 67 pmol/l, TSH lower than 0.05 µU/ml (norm: 0.11-5), anti-TSH receptor antibodies at 56% (norm: 0-15%). The Technetium-99m scintigraphy showed an asymmetry of the gland in favor of the left lobe and the ultrasound, a left lobe of heterogeneous structure without nodule. The diagnosis of hyperthyroidism was retained in a young girl and treatment with synthetic antithyroid drugs was carried out, with a rapid euthyroidism. The evolution remained favorable at one-year follow-up. CONCLUSION: Hyperthyroidism is one of the rare complications of radiotherapy. It is necessary to think about it and to carry out a thyroid hormone assay during the monitoring of the patients irradiated to avoid a diagnostic errancy leading to psychotropic treatments sometimes avoidable.