Thyrotoxic hypokalaemic periodic paralysis

A 24-year-old male Chinese student from southern China presented with sudden onset of generalized weakness. The evening before admission he had played football for 3 hours, and eaten a Chinese takeaway plus two hamburgers. He awoke in the early hours of the following morning unable to move his arms or legs. There was no history of any recurring illness and in particular there were no symptoms suggestive of hyperthyroidism. On examination the only abnormality was a profound symmetrical muscle weakness more marked proximally than distally (Medical Research Council (MRC) classification grade 1–2). Sensation to light touch and pinprick was normal. There were no signs of thyrotoxicosis. Laboratory investigations revealed the following (normal values in parentheses): serum potassium 1.2 mmol/litre (3.5–5.0); urinary potassium 14 mmol/litre (20–60); phosphate 0.18 mmol/litre (0.8–1.45); sodium, urea, and creatinine levels were normal. Electrocardiogram showed first degree atrioventricular block, prolonged QT int...