• A progressive degenerative myopathy has been well described in hypokalemic periodic
paralysis but is not as widely recognized in hyperkalemic periodic paralysis. We studied four
families with the latter disease in which some members developed a progressive myopathy.
Episodes of paralysis were prolonged, lasting for months in some cases, and in one case
paralysis was sufficiently severe to require ventilatory support. The progressive myopathy
tended to develop at a time when attacks of paralysis were decreasing in frequency. Muscle …