Diagnosis of familial hypokalemic periodic paralysis: role of the potassium exercise test.

Familial hypokalemic periodic paralysis (FHOPP) is a rare, dominantly inherited disease, the diagnosis of which may require the induction of paralysis. We studied whether the increase in plasma potassium concentration during exercise can be used in the diagnosis of FHOPP. Potassium concentration increased 0.3 +/- 0.1 mEq/l in patients with FHOPP and 0.6 +/- 0.1 mEq/l in healthy controls (p < 0.001) during a 10-minute bicycle exercise test, and 0.3 +/- 0.1 mEq/l in patients with FHOPP and 0.8 +/- 0.2 mEq/l in healthy controls (p < 0.001) during a 30-minute bicycle exercise test. We conclude that the potassium exercise test may be useful in the diagnosis of FHOPP.