3,4‐Diaminopyridine is more effective than placebo in a randomized,double‐blind,cross‐over drug study in LEMS

The purpose of this study was to investigate the clinical and electrophysiological efficacy of 3,4‐diaminopyridine (DAP) in patients with Lambert–Eaton myasthenic syndrome (LEMS) in a randomized, double‐blind, cross‐over drug trial. The diagnosis of LEMS was made based on the combination of fluctuating muscle weakness, diminished or absent reflexes, and more than 60% increment of the compound muscle action potential (CMAP) amplitude after brief exercise or 50‐HZ stimulation on a repetitive nerve stimulation (RNS) test. Evaluations were done at baseline, with placebo, and with 3,4‐DAP (up to 75–80 mg/day). Assignment of placebo or 3,4‐DAP was done in a double‐blinded manner. Measurements included subjective symptoms score, objective clinical measurements LEMS classification, muscle strength score, quantitative myasthenia gravis (QMG) score] and RNS test and single‐fiber electromyography (SFEMG). The differences between placebo and baseline values (placebo change) were compared with the differences between 3,4‐DAP and baseline or placebo values (DAP change). Seven patients with LEMS (QMG score >9) participated in the study. One patient had major side‐effects with 3,4‐DAP and withdrew from the study. Statistically significant efficacy was noted with DAP change (N = 13) compared with placebo change (N = 7) according to the subjective symptoms score (P = 0.01), LEMS classification (P < 0.001), muscle strength score (P < 0.006), QMG score (P = 0.02), and CMAP (P = 0.03). For long‐term treatment, 2 patients preferred 3,4‐DAP, 1 chose guanidine hydrochloride, 1 preferred pyridostigmine, and 2 chose no treatment. A randomized, double‐blind, cross‐over drug trial of 3,4‐DAP showed significant efficacy over placebo in patients with LEMS. As a long‐term treatment, however, not all patients preferred this drug. Muscle Nerve, 2009