Thyrotoxic periodic paralysis in a Caucasian man: recognition and diagnosis.

Periodic paralyses are uncommon disorders characterized by episodic muscle weakness, often with hypokalemia. Thyrotoxic periodic paralysis (TPP) is the most common and is rarely seen in the Caucasian population; the relative unfamiliarity of TPP among physicians in the United States may lead to initial errors in diagnosis. This article presents the case of a 25-year-old white man with frequent episodes of skeletal muscle weakness and cramping, associated with profound hypokalemia. Laboratory evaluation demonstrated primary hyperthyroidism, and a diagnosis of TPP was made. The disorder is found more commonly in men between the ages of 20 and 40. Hypokalemia is the most consistent laboratory abnormality, representing a transcellular shift rather than a total body deficit; the exact mechanism is unknown. The exercise test demonstrates distinct electromyographical abnormalities in those with periodic paralysis. The definitive treatment of TPP is establishing a euthyroid state.