Treatment for periodic paralysis

BACKGROUND: Primary periodic paralyses are rare inherited muscle diseases characterised by episodes of flaccid weakness affecting one or more limbs, lasting several hours to several days, caused by mutations in skeletal muscle channel genes. OBJECTIVES: The objective of this review was to systematically review treatment of periodic paralyses. SEARCH STRATEGY: We searched the Cochrane Neuromuscular Disease Group Trials Register, MEDLINE (from January 1966 to July 2007), and EMBASE (from January 1980 to July 2007) and any other available international medical library sources from the University of Milan for randomised trials. SELECTION CRITERIA: We included randomised (including cross-over studies) and quasi-randomised trials in participants with primary periodic paralyses, in which any form of treatment, including physical therapy and alternative therapies, was compared to placebo or another treatment. DATA COLLECTION AND ANALYSIS: Our primary outcome measure was the change in attack severity or frequency by eight weeks from the start of treatment. Our secondary outcome measures were: change in muscle strength and mass; change in Quality of Life, using Short Form 36 (SF36) or similar; preference of treatment strategy; adverse effects at eight weeks. MAIN RESULTS: Three studies met our inclusion criteria. In one study dichlorphenamide (DCP) vs placebo was tested in two groups of participants: 42 with hypokalemic periodic paralysis (HypoPP) and 31 with hyperkalemic periodic paralysis (HyperPP), based on clinical criteria. Thirty-four of 42 participants with hypokalemic periodic paralysis completed both treatment phases. For the 34 participants having attack rate data for both treatment phases, the mean improvement in attack rate (P = 0.02) and severity-weighted attack rate (P = 0.01) on DCP relative to placebo were statistically significant. Fifteen preferred DCP, three placebo and six their baseline medication. Twenty-four of 31 participants with hyperkalemic periodic paralysis completed both treatment phases: for the 16 participants who had attack rate data for both treatment phases, the mean improvement in attack rate (P = 0.006) and in severity-weighted attack rate (P = 0.02) on DCP relative to placebo were significant. Fifteen preferred DCP, one placebo and five their baseline medication. Acetazolamide proved to improve muscle strength in eight participants with HypoPP in one other study and pinacidil, a potassium channel opener, also improved muscle strength in 2/4 participants with HypoPP in a third study. AUTHORS'' CONCLUSIONS: The largest included study that met our inclusion criteria suggested that DCP was effective in the prevention of episodic weakness in both hypokalemic and hyperkalemic periodic paralyses. The other two studies provide some evidence that either acetazolamide or pinacidil may improve muscle strength. However we still lack sufficient evidence to provide full guidelines for the treatment of people with periodic paralysis.