Multifocal Motor Neuropathy: Disease Stabilisation on Quinidine

Objective:To describe the serendipitous effect of quinidine on intravenous immunoglobulin (IVIG) dependent multifocal motor neuropathy (MMN).Background:MMN is a rare immune-mediated demyelinating neuropathy. A consistent feature is high IVIG requirement, with latter treatment resistance. Other immunomodulatory agents have not shown consistent benefit. A putative pathological mechanism involves hyperpolarisation-depolarisation of nerve beyond areas of conduction block. We report a case of improved MMN disease control with the addition of quinidine, an anti-arrhythmic agent with membrane stabilizing and immunogenic properties.Methods:A 51 year old patient with MMN had received IVIG for over 8 years, with gradual decline in disease control after several years of therapy. Mycophenolate mofetil was not beneficial. Rituximab was added 6 years after IVIG. At 50 years, he was commenced on quinidine for an unrelated episode of ventricular fibrillation (VF). IVIG and rituximab requirements and treatment response were documented prior to, and following, treatment with quinidine.Results:Prior to quinidine therapy there was chronic mild weakness of right biceps and left finger abduction/adduction on IVIG (2g/kg/month) and regular rituximab. Disease control reproducibly deteriorated with early B-cell recovery, with increasing end of IVIG cycle weakness, prompting further re-dosing with rituximab (2g over two weeks) approximately 6 monthly. He was 4 months post-rituximab therapy at time of VF arrest. He had developed recurrence of progressive weakness, despite B-cell depletion (u003c1[percnt] total lymphocytes). One month following quinidine treatment, strength in previously weak muscles improved. He was maintained on monthly IVIG, and remained clinically stable for the next 12 months without requiring additional rituximab. We discuss proposed pathological mechanisms of MMN and potential mechanisms of disease stabilization induced by quinidine.Conclusions:Quinidine therapy may provide additional benefit in MMN. Further studies are needed to accurately describe treatment effect and response. Disclosure: Dr. Leong has nothing to disclose. Dr. Saw has nothing to disclose. Dr. O9Connor has nothing to disclose. Dr. Nolan has nothing to disclose. Dr. John has nothing to disclose.