Multifocal motor neuropathy: Current concepts and controversies

Abstract

Multifocal motor neuropathy (MMN) is now a well-defined purely motor multineuropathy characterized by the presence of multifocal partial motor conduction blocks (CB), frequent association with anti-GM1 IgM antibodies, and usually a good response to high-dose intravenous immunoglobulin (IVIg) therapy. However, several issues remain to be clarified in the diagnosis, pathogenesis, and therapy of this condition including its nosological position and its relation to other chronic dysimmune neuropathies; the degree of CB necessary for the diagnosis of MMN; the existence of an axonal form of MMN; the pathophysiological basis of CB; the pathogenetic role of antiganglioside antibodies; the mechanism of action of IVIg treatments in MMN and the most effective regimen; and the treatment to be used in unresponsive patients. These issues are addressed in this review of the main clinical, electrophysiological, immunological, and therapeutic features of this neuropathy.

Clinical Reasoning: A 34-year-old man with recurrent limb weakness

“…Slightly to moderately increased serum creatine kinase activity is observed in up to 67% of patients with MMN. 2 At this stage, presumptive diagnosis of motor neuropathy, without any other identified cause, justified the treatment with IV immunoglobulin (IVIg).…”

Inflammatory Demyelinating Neuropathies and Neuropathies Associated with Monoclonal Gammopathies: Treatment Update

“…Whether patients who have MMN and patients who have Lewis Sumner syndrome have the same disorder with varying degrees of sensory involvement has been debated. 31,32 Although there are a number of reasons to consider MMN to be a variant of CIDP, it appears to be a distinct clinical entity with a different therapeutical strategy. The pathognomonic feature of this condition is the presence of multiple focal motor nerve conduction blocks and high titer of IgM anti-GM1 antibodies in up to 85% of MMN patients.…”

Multifocal motor neuropathy: and then, 20 years later IVIg therapy

“…However, there The selection of outcome measures to be used in therapeutic trials is difficult in the setting of multifocal motor neuropathy. The disability in multifocal motor neuropathy mainly affects the upper limbs, but may involve the lower limbs [2,4]. In addition, outcome measures should also cover impairment and quality of life.They should be simple, valid, reliable and responsive, and correlate with disease severity.…”

“…IVIg infusions, given at 0.4 g/ kg/day for 5 consecutive days were followed by an early and often dramatic improvement of the motor deficit in the affected motor nerves and sometimes a reduction of conduction block in the electrophysiological studies. However, the presence of definite conduction block is not a necessary condition to observe a response to IVIg therapy [29] and treatment does not appear to affect serum anti-GM1 antibody titres [2].…”

“…It is characterised by slowly progressive, predominantly distal, asymmetric limb weakness and wasting, predominant in the arms, with muscle cramps and fasciculations, within an anatomical distribution of individual motor nerves, with minimal or no sensory involvement [2][3][4]. It is a rare condition affecting no more than 1-2 persons per 100 000, more frequent in men than women with an approximate sex ratio in reported patients of 2.6 :1, as found in a recent questionnaire study conducted in France [5].…”