Adynamia episodica and paralysis periodica paramyotonica

We studied hyperkalemic attacks in one family with adynamia episodica (AE) and one family with paralysis periodica paramyotonica (PPP). Under exercise, serum potassium increased as in healthy subjects. Thiazide did not affect this increase. Thirty minutes after exercise, a second potassium increase occurred, but could be prevented by thiazide and not by mexiletine. After cooling, muscle relaxation time was normal in AE but increased up to 100 times in PPP; this cooling effect was prevented by mexiletine. Although hyperkalemic attacks are similar in AE and in PPP, the membrane defect in PPP seems more complex.