Unusual case of weakness in the UK

A healthy 35-year-old Vietnamese man presented with acute tetraparesis. He was watching television when suddenly he could not mobilise. As the weakness progressed overnight he attended the accident and emergency department. Observations were normal. He denied any pain, headache, vomiting, diarrhoea or use of laxatives or illicit drugs. Neurological examination revealed global weakness in all four limbs ranging from 0 to 3/5. Reflexes were suppressed. Examination of cranial nerves and of other systems was unremarkable. However, laboratory results showed a hypokalaemia of 2.3 (3.5-5.5 mmol/l) on admission. ECG first showed U waves and Mobitz type 1 but this resolved to sinus rhythm. On further questioning, he revealed a recent weight loss of 9 kg despite an increase in appetite. Thyroid function tests revealed free T4 57 (12-22 pmol/l) with thyroid-stimulating hormone undetectable. He was treated with potassium replacement and carbimazole and his symptoms resolved completely 8 days post-admission. The patient was diagnosed with hypokalaemic thyrotoxic periodic paralysis.