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A 14-year-old Chinese girl was referred to us for assessment of her thyrotoxicosis before corrective surgery of genu varus. On questioning, she mentioned significant weight loss with occasional palpitations. She had also experienced episodic lower limb proximal muscle weakness, but there was no history of paralysis.
Physical examination showed sinus tachycardia of 110 beats/min. There was no lid retraction or lid lag. Her goitre was enlarged three-fold with audible bruit, but there was no retrosternal extension. Eye examination revealed no evidence of Graves' ophthalmopathy. Abdominal examination was normal. There was no lymphadenopathy, splenomegaly nor pretibial myxoedema. Her proximal muscle power was grade 4/5 and the jerks were all brisk.
Investigations showed a raised free thyroxine of >170 pmol/l (normal range 10-19 pmol/l) and a suppressed thyrotropin of <0.03 mIU/l (0.35-5.5 mIU/l). Chest X-ray, however, revealed a mediastinal shadow with clear lung field. Complete blood count and routine biochemistry were normal. Acetylcholamine receptor antibody was...