Radioiodine Treatment For Hyperthyroidism In A Patient With Pendred Syndrome

Objective: To report a case of Pendred syndrome accompanied by hyperthyroidism that was treated with radioiodine. Pendred syndrome is an autosomal recessive disorder characterized by bilateral sensorineural hearing impairment, goiter, and impaired iodide organification. The majority of patients with Pendred syndrome are euthyroid or hypothyroid, and hyperthyroidism is rare. Thus far, there are no reported cases of Pendred syndrome with 131I-treated hyperthyroidism.Methods: A 39-year-old woman with congenital hearing impairment visited our clinic because of easy fatigability and body weight loss.Results: She had a diffuse goiter (estimated thyroid weight, 65 g) and subclinical thyrotoxicosis. 99mTechnetium pertechnetate scintigraphy revealed diffuse thyroidal uptake, but thyroid autoantibodies were absent. Since the therapeutic response to a single 131I dose was poor, the patient underwent a second 131I dose (13 mCi each) for hyperthyroidism. Seven years after the second 131I dose, she was euthyroid and her thyroid was still relatively large (37 g). She was later diagnosed with Pendred syndrome due to a homozygous SLC26A4 (pendrin) mutation.Conclusion: The therapeutic effect of radioiodine on hyperthyroidism may be low in patients with Pendred syndrome as a result of impaired iodide uptake into the follicular lumen by the mutated pendrin.