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.