A male junior high school student presented with failure to gain weight and acceleration of growth for 2 years. Free triiodothyronine and free thyroxine levels were elevated, and the thyroid-stimulating hormone (TSH) level was suppressed. TSH receptor antibody (TRAb) and thyroid-stimulating antibody were negative. On I-123 thyroid scintigraphy, iodine uptake was most pronounced in the upper pole of the right lobe. The patient was initially diagnosed with asymmetrical TRAb-negative Graves' disease (GD). His thyroid hormone level normalised with potassium iodide (KI) alone, and he became TRAb-positive 4 months after the initiation of KI therapy. This case demonstrates a rare presentation of GD that was initially TRAb-negative, which had asymmetrical iodine uptake on a thyroid scan and was confirmed to be TRAb positivity during the follow-up. KI monotherapy could be one of the effective treatment options for GD that is initially TRAb-negative.
Keywords: Endocrine system; Hyperthyroidism; Thyroid disease.
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