Marieke van Rosmalen

Clinical outcomes in MMN 27 2 INTRODUCTION Multifocal motor neuropathy (MMN) is a pure motor disorder characterized by slowly progressive asymmetric distal weakness mainly in the hands, the absence of upper motor neuron signs and presence of one or more abnormal ancillary investigations, i.e. abnormal nerve conduction or conduction block (CB), thickening or T2 hyperintensity on magnetic resonance imaging (MRI) of the brachial plexus, sonographic nerve thickening, increased protein content in the cerebrospinal fluid (CSF) or the presence of anti-GM1 IgM antibodies in serum. 1–5 Administration of intravenous or subcutaneous immunoglobulins transiently improves muscle strength and maintenance treatment is therefore needed. 6–10 Consensus criteria have facilitated diagnosis of MMN and shortened diagnostic delays, but we know less of the disease course and outcome. 5,11 Early case reports suggested that its course is not benign in individual patients, but few studies have longitudinally addressed natural history in larger patients cohorts. 12–14 Early treatment may improve long-term outcome, but accumulating axonal damage nevertheless results in significant disability in up to one fifth of patients. 11,15 More detailed insight in MMN’s clinical course would help to identify correlates of worse outcome and thereby patients at higher risk for developing severe deficits, and eventually to investigate efficacy of other treatment approaches. We have previously reported the characteristics of a relatively large cross sectional cohort of patients with MMN in the Netherlands. 11 In order to gain more insight in the clinical course of MMN, we performed a combined cross-sectional and follow-up study in a cohort of 100 patients with the aim to identify factors that predict a progressive disease course of MMN. METHODS Study design and patients This cross-sectional cohort study was performed between May 2015 and February 2016 in the University Medical Center (UMC) Utrecht, a large tertiary referral center for neuromuscular disorders in The Netherlands. We invited all patients listed in the MMN database of the UMC Utrecht who met the following inclusion criteria: 1) a diagnosis of definite, probable or possible MMN according to the EFNS/PNS criteria and 2) age ≥ 18 years. 5 A subgroup of our patients previously participated in a similar cross-sectional cohort study in 2007. 11 The local medical ethics committee of the UMC Utrecht approved the research protocol (NL50354.041.14). All included patients gave written informed consent.