Multifocal Motor Neuropathy (MMN)

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An overview of MMN1

What is MMN?

Multifocal motor neuropathy (MMN) is an acquired, autoimmune, chronic, asymmetric motor polyneuropathy affecting predominantly (upper) distal extremities. The course of the disease is slowly progressive, extending over years without spontaneous remission.^1,2

MMN is a rare disorder with a prevalence of <1 in 100,0001,2

MMN is more common in males (the male-to female ratio is about 3:1).1

The median age of disease onset is 40-50 years (ranging between teenage years to the seventh decade).1

The site of onset is most commonly in the distal upper limb (60%–80%) while a smaller portion of patients have distal lower limb onset (15%–30%).1

Multifocal motor neuropathy typically presents with asymmetric, chronic, or stepwise progressive weakness. Finger extensors are more commonly affected than flexors, and weakness may follow the distribution of individual nerves. Cold paresis, a worsening of weakness with cold exposure, is frequently reported. Muscle atrophy develops over time but is often less pronounced than expected compared to the degree of weakness. Fasciculations, cramps, and reduced or normal reflexes are common, while significant sensory loss is usually absent.1

Pathophysiology^1,2

Multifocal motor neuropathy (MMN) is believed to arise primarily from dysfunction at the node of Ranvier rather than from primary damage to the myelin sheath or the axon itself. Disruption at the nodal region interferes with the normal transmission of electrical impulses along the nerve, resulting in the characteristic electrophysiological feature of MMN on nerve conduction studies (NCS), namely conduction block (CB).^1,2

Immunoglobulin M (IgM) antibodies directed against monosialotetrahexosylganglioside (GM1) are detectable in approximately 40% or more of individuals with MMN. Patients who are positive for anti-GM1 antibodies tend to exhibit more pronounced weakness, greater functional impairment, and a higher likelihood of secondary axonal degeneration compared with seronegative patients. It has been proposed that these antibodies trigger complement activation at the nodes of Ranvier, leading to nodal injury, conduction block, and subsequent muscle weakness.^1,2

Diagnosis of MMN3-5

Diagnosis is made based on clinical and electrodiagnostic methods. It can be excluded, in case of upper motor neuron signs, marked bulbar involvement, sensory impairment more marked than minor vibration loss in the lower limbs and diffuse symmetric weakness during the initial weeks.

Diagnostic criteria for MMN^3-5

The treatment options for people with MMN are limited.

In contrast to CIDP, MMN usually does not respond to steroids or plasma exchange.³

So far, only immunoglobulins have been consistently effective.^3,5

Treatment of MMN

The EFNS and the PNS recommend intravenous immunoglobulin as the core initial and long-term treatment for MMN.3,5

IVIg (e.g., octagam®)3

First line treatment (when disability is sufficiently severe to warrant treatment)
2 g/kg given over 2-5 days
If initial treatment is effective, repeat IVIg treatment in selected patients
The frequency of IVIg maintenance therapy should be guided by the response. Typical regimens are 1 g/kg every 2-4 weeks or 2 g/kg every 1-2 months

Immunosuppressants3

May be considered if IVIg is not sufficiently effective
However, no evidence for beneficial effect from clinical trials

Cyclophosphamide3

The toxicity makes it a less desirable option

Corticosteroids3

Not recommended

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Octagam® for MMN

Tolerability: 7 out of 18 patients who were treated with octagam® showed adverse events that were assessed as possibly or probably related to treatment.5

Efficacy: 94% of patients with MMN who were treated with octagam®5% either improved (61.1%, MRC score, 11 patients out of 18) or remained clinically stable (33.3%; MRC score, 6 patients out of 18).6

References

Claytor B, et al. Muscle Nerve 2025;71(4):512-534.
Allen JA, et al. Mayo Clinic proceedings. Innovations, quality & outcomes 2024;8:74–81.
Van Schaik I.N. and Joint Task Force of the EFNS and the PNS. J Peripher Nerv Syst 2020;15:295–301
Lawson VH and Arnold DW. Neuropsychiatric Disease and Treatment. 2014:10 567-576
Beadon K, et al. Curr Opin Neurol 2018, 31:559–564.
Franques J, et al. Efficacy and tolerance of octagam® in multifocal motor neuropathy with conduction block (MMN). Poster presented at the INC Rotterdam 2012.

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IMPORTANT: The information on this website is based on the European Summary of Product Characteristics (EU SmPC).

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