An Electrocardiogram Triad in Thyrotoxic Hypokalemic Periodic Paralysis

Abstract

A 37-year-old Asian man presented to the emergency department with acute onset of bilateral lower-extremity weakness. Physical examination was notable for marked reduction in proximal muscle strength, with decreased deep tendon reflexes. Initial laboratory tests showed a potassium level of 1.3 mEq/L (normal range, 3.7 to 5.2 mEq/L), thyroid-stimulating hormone level <0.03 μIU/mL (normal range, 0.4 to 5.0 μIU/mL), total thyroxine of 21.8 μg/dL (normal range, 4.8 to 10.8 μg/dL), and free thyroxine level of 5.7 ng/dL (normal range, 0.8 to 1.8 ng/dL). The 12-lead ECG taken immediately after presentation was notable for sinus tachycardia, first-degree atrioventricular conduction delay, ST depressions, and prolonged T/U segments (Figure 1). Figure 1. Twelve-lead ECG shows …