Multifocal motor neuropathy (MMN) is a rare, purely motor neuropathy with a prevalence of approximately 0.6 per 100,000 and a median age of onset of 40 years.1 Men are more likely than women to be affected, in a ratio of 2.7:1 and are usually diagnosed at an earlier age.1 Patients with MMN typically present with asymmetrical, predominantly distal limb weakness that follows individual nerves. There is no apparent sensory loss and weakness usually starts in the forearm or hand muscles, though the first symptoms may occur in the distal leg and upper arm. Respiratory and bulbar muscles are unaffected and patients have a normal life expectancy. However, since MMN is a progressive disorder, most patients eventually develop severe fatigue and weakness in the arm muscles, resulting in disability that can seriously impair daily functioning and quality of life.
Unlike other motor neuropathies such as motor neurone disease (MND), MMN is treatable with intravenous immunoglobulin (IVIg).2 Most patients require regular infusions in order to maintain clinical response and the aim of this review is to consider the effectiveness and safety of long-term or maintenance treatment of MMN with IVIg.
The terms ‘multifocal motor neuropathy’, ‘treatment’, ‘long term’, ‘maintenance’ and ‘IVIg’ were used to conduct a PubMed search of articles published in English language journals between 1 January 1980 and 31 December 2011 (see Table 1). Papers were excluded ifthey were single case reports, or were superseded by subsequent publications following up the same group of patients.
The manual search of the results of the PubMed literature searchidentified a total of 14 studies concerning the long-term or maintenance treatment of MMN with IVIg. Three papers were excluded:
- a case report in one patient;3
- a publication concerning six patients included in a subsequent, larger study;4,5
- and a study of dose titration in patients on maintenance IVIg.6
The remaining 11 studies listed in Table 2 were included in the analysis.1,5,7–15 All were retrospective, observational studies, except for one cross-sectional, descriptive study.
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