A Cochrane review included 4 RCTs with a total of 54 patients with Lambert-Eaton myasthenic syndrome. Trials compared 3,4-diaminopyridine with placebo in 3 cross-over and one parallel group trials. One of these trials (n=9) also assessed pyridostigmine in conjunction with 3,4-diaminopyridine. A further cross-over trial compared intravenous immunoglobulin (IVIg) to placebo in 9 participants. Four trials of 3,4-diaminopyridine reported significant improvement in the primary outcome, muscle strength score, or myometric limb measurement for between hours and a week following treatment, and significant improvement in resting compound muscle action potential (CMAP) amplitude following 3,4-diaminopyridine, compared with placebo. A meta-analysis of the primary endpoint showed Quantitative Myasthenia Gravis (QMG) muscle score, assessed between 3 and 8 days, likely to improve by a mean of 2.44 points (95% CI 3.6 to 1.22). Meta-analysis of the secondary endpoint, CMAP amplitude, also showed a mean improvement of 1.36 mV (95% CI 0.99 to 1.72) over the same period. A single cross-over trial reported significant improvement in myometric limb strength in 3 strength measures (p = 0.017 to 0.038), lasting for up to 8 weeks, and non-significant improvement in mean resting CMAP amplitude with IVIg compared to placebo.
Comment: The quality of the evidence is downgraded by study quality (unclear allocation concealment), inconsistency (heterogeneity in outcomes) and imprecise results (limited study size for each comparison).