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-β1a, 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.