Rebound Hyperkalemia After Potassium Repletion in Thyrotoxic Periodic Paralysis: A Case Report and Review of Management Implications.

Thyrotoxic periodic paralysis (TPP) is a potentially life-threatening complication of hyperthyroidism. It is characterized by hypokalemia-induced muscle weakness that typically begins in the proximal lower limbs and may progress to paralysis of all four extremities and involvement of the respiratory muscles. We present a case of a 37-year-old man with a history of TPP, presenting with acute muscle weakness and hypokalemia. The patient reported acute-onset bilateral lower extremity weakness from the previous day. Physical examination revealed normal deep tendon reflexes, but marked muscle weakness was observed in both lower limbs. Laboratory workup revealed severe hypokalemia at 2.1 mEq/L and thyrotoxicosis, while the electrocardiogram showed a prolonged QTc interval. The patient received thiamazole, potassium iodide, and propranolol for thyrotoxicosis and a total dose of 122 mEq of potassium repletion. His potassium level rose from 1.7 mEq/L to 5.6 mEq/L within six hours post-repletion cessation, highlighting the risk of rebound hyperkalemia and the importance of close monitoring. This case underscores the danger of rebound hyperkalemia after aggressive potassium repletion in TPP and supports a cautious, stepwise correction strategy.