3,4-diaminopyridine base effectively treats the weakness of Lambert-Eaton myasthenia

Introduction: 3,4-diaminopyridine has been used to treat Lambert-Eaton myasthenia (LEM) for 30 years despite the lack of conclusive evidence of efficacy. Methods: We conducted a randomized double-blind placebo-controlled withdrawal study in patients with LEM who had been on stable regimens of 3,4-diaminopyridine base (3,4-DAP) for3 months. The primary efficacy endpoint was >30% deterioration in triple timed up-and-go (3TUG) times during tapered drug withdrawal. The secondary endpoint was self-assessment of LEM-related weakness (W-SAS). Results: Thirty-two participants were randomized to continuous 3,4-DAP or placebo groups. None of the 14 participants who received continuous 3,4-DAP had>30% deterioration in 3TUG time versus 72% of the 18 who tapered to placebo (P<0.0001). W-SAS similarly demonstrated an advantage for continuous treatment over placebo (P<0.0001). Requirement for rescue and adverse events were more common in the placebo group. Discussion: This trial provides significant evidence of efficacy of 3,4-DAP in the maintenance of strength in LEM. Muscle Nerve57: 561-568, 2018