A case report of sudden-onset upper and lower extremity weakness.

Thyrotoxic hypokalemic periodic paralysis is characterized by acute attacks of muscle paralysis, hypokalemia, and thyrotoxicosis. It is a medical emergency, as fatal and life-threatening ventricular arrhythmia associated with hypokalemia has been reported. A 24-year-old man presented with severe lower extremity weakness, which progressed to his trunk and arms. He denied any associated symptoms and had no history of a similar episode or predisposing condition. The physical examination was significant for bilateral extremity weakness, more severe in the lower as compared to the upper extremities. The rest of the neurologic exam was normal. A small, smooth, nontender goiter was palpated. Laboratory data was significant for a potassium level of 2.0 mEq/L. Final lab data revealed a thyroid panel consistent with hyperthyroidism. Once the patient's potassium level normalized after repletion, he recovered his strength and was able to walk again. He was diagnosed with thyrotoxic hypokalemic periodic paralysis, a potentially lethal complication of hyperthyroidism. Because it is reversible with treatment of hyperthyroidism, it is imperative that this condition be considered, recognized and managed appropriately.