Multifocal Motor Neuropathy: Current Therapies and Novel Strategies
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LEADING ARTICLE
Multifocal Motor Neuropathy: Current Therapies and Novel Strategies Eduardo Nobile-Orazio • Francesca Gallia
Published online: 21 March 2013 Ó Springer International Publishing Switzerland 2013
Abstract Multifocal motor neuropathy (MMN) is a purely motor mononeuritis multiplex characterized by the presence of conduction block on motor but not on sensory nerves and by the presence of high titers of anti-GM1 antibodies. Several data point to a pathogenetic role of the immune system in this neuropathy, although this has not yet been proved. Several uncontrolled studies and randomized controlled trials have demonstrated the efficacy of therapy with high-dose intravenous immunoglobulin (IVIg) in MMN. However, this therapy has a short-lasting effect that needs to be maintained with periodic infusions. This can be partly overcome by the use of subcutaneous immunoglobulin (SCIg) at the same dose. The high cost and need for repeated infusions have led to the search for other immune therapies, the efficacy of which have not yet been confirmed in randomized trials. In addition, some therapies, including corticosteroids and plasma exchange, are not only ineffective but have been associated with clinical worsening. More recently, a number of novel therapies have been investigated in MMN, including interferon-b1a, the anti-CD20 monoclonal antibody rituximab and the complement inhibitor eculizumab. Preliminary data from open-label uncontrolled studies show that some patients improve after these therapies; however, randomized controlled trials are needed to confirm efficacy. Until then, IVIg (and SCIg) remains the mainstay of treatment in MMN, and the use of other immune therapies should only be considered for patients not responding to, or becoming resistant to, IVIg.
1 Introduction Multifocal motor neuropathy (MMN) is a purely motor mononeuritis multiplex characterized by the presence of multifocal partial motor conduction blocks (CB), frequent association with anti-GM1 immunoglobulin-M (IgM) antibodies and usually good response to high-dose intravenous immunoglobulin (IVIg) therapy [1, 2]. Although MMN has been reported previously in a few patients [3–5], Pestronk et al. [6] first introduced the term MMN and highlighted its frequent association with anti-GM1 IgM antibodies and response to immune therapies. In the early 1990s, a few groups reported on the improvement of MMN after therapy with high-dose IVIg, the efficacy of which was later confirmed in randomized controlled trials (RCTs) [7]. Other therapies have also been reported to be variably effective in case reports or in small series of patients, but the efficacy has, thus far, not been confirmed in RCTs. The aim of this review is to briefly summarize the clinical presentation, electrophysiological features and pathogenesis of MMN. The mechanism of action, efficacy and limits of available therapies are reviewed, as are the mechanism of action of potential new treatments and the preliminary data on their efficacy.
2 Multifocal Motor Neuropathy (MMN) 2.1
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