Abstract
A male patient aged in his early twenties presented to the emergency department (ED) with quadriparesis. He was ordinarily fit and well and had exercised and eaten a carbohydrate rich meal the evening before. His point-of-care venous blood sample on arrival to the ED showed hypokalaemia of 1.6 mmol/L. (normal range=3.5–5.0 mmol/L). He was put on a cardiac monitor and started on an intravenous infusion of potassium chloride. With the benefit of hindsight, his male sex, particular features in his history and his initial ECG all pointed to a differential diagnosis of thyrotoxic periodic paralysis (TPP), although a differential diagnosis of a first attack of familial hypokalaemic paralysis was considered. As urgent thyroid function tests were sent promptly, there was minimal delay in reaching a diagnosis of TPP and promptly starting propranolol as a safe and more effective means of reversing TPP, followed by definitive treatment with carbimazole.