Abstract
Multifocal motor neuropathy (MMN) is a rare inflammatory neuropathy characterized by progressive, asymmetric distal limb weakness and conduction block (CB). Clinically MMN is a pure motor neuropathy, which as such can mimic motor neuron disease. GM1-specific IgM antibodies are present in the serum of approximately half of all MMN patients, and are thought to play a key role in the immune pathophysiology. Intravenous immunoglobulin (IVIg) treatment has been shown to be effective in MMN in five randomized placebo-controlled trials. Despite long-term treatment with intravenous immunoglobulin (IVIg), which is efficient in the majority of patients, slowly progressive axonal degeneration and subsequent muscle weakness cannot be fully prevented. In this review, we will discuss the current understanding of the immune pathogenesis underlying MMN and how this may cause CB, available treatment strategies and future therapeutic targets.
Highlights
Multifocal motor neuropathy (MMN) is a rare immunemediated, pure motor neuropathy with a prevalence of at least 0.6 per 100,000 individuals [1]
In a recent study we found anti-GM1 antibodies in serum of at least 50 % of a large cohort of patients with MMN using a very specific enzyme-linked immunosorbent assay (ELISA) protocol [1]
Besides immune modulatory therapies, improving conduction properties of nerves may be another approach. 3,4 Diaminopyridine is a broad-spectrum inhibitor of fast voltage-activated K+ (Kv) channels and improved action potential propagation in in vitro models of demyelination. It had no significant change on clinical outcome or on conduction blocks in small patient groups with chronic inflammatory demyelinating polyneuropathy (CIDP), MMN and Guillain-Barre syndrome (GBS) and this was confirmed in a double blind placebo controlled study [73, 74]
Summary
Multifocal motor neuropathy (MMN) is a rare immunemediated, pure motor neuropathy with a prevalence of at least 0.6 per 100,000 individuals [1]. In contrast to other immune-mediated polyneuropathies such as the Guillain-Barre syndrome (GBS) or chronic inflammatory demyelinating polyneuropathy (CIDP), onset of MMN does not occur in childhood or old age. The presence of antibodies against GM1 and the favourable response to IVIg treatment support an immune mediated pathophysiology. MMN has a distinct overlap in clinical features with acute motor axonal neuropathy (AMAN), the pure motor axonal form of GBS, implying an analogy in underlying disease mechanisms We will focus on the immune pathophysiology of MMN and on CB, and how this knowledge may help to develop novel therapeutic strategies
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