hypokalemic periodic paralysis: age of onset in a retrospective study

primary hypokalemic periodic paralysis is a familial channelopathy inherited as an autosomal dominant trait. the first attack of paralysis may be evolved at any age, but has been reported to be most common in the second decade, so that some authorities believe that an episodic weakness beginning after age 25 is almost never due to primary periodic paralysis. in this retrospective study, we reviewed 50 patients admitted in two hospitals of tehran university of medical sciences during 1992-2001 with acute flaccid weakness and hypokalemia, twenty-three of whom fulfilled our inclusion and exclusion criteria. two patients showed first attack below age 15, 8 in 15-20, 4 in 20-25, 3 in 25-35, 4 in 35-45, and 2 beyond age 45. in our study, in contrast to previous ones, the first attack was beyond age 20 in 13 patients (56.5%) and beyond 25 in 9 (39 %). age at first attack is more than other studies, which seems to be due to a difference between our epidemiological characteristics compared to that in the west. in other words, in our epidemiological condition, periodic weakness, although started beyond second decade of age, could be due to primary periodic paralysis if secondary hypokalemia had been ruled out.