What is MMN?
Multifocal motor neuropathy (MMN) with conduction block is an acquired, chronic, asymmetric motor neuropathy affecting predominantly distal extremities, arms and legs. The course of the disease is slowly progressive, extending over years without spontaneous remission.
MMN is a rare disorder, and prevalence estimates range from 0.3-3 cases in 100.16
MMN is more common in males (the male-to female ratio is about 3:1).17
The median age of disease onset is 40 years (ranging between 20 and 50 years). Pediatric patients with MMN are extremely rare.18
The site of onset is in 2/3 of cases in the distal arm/hand, in one third in the distal leg, in 5% the proximal arm, but never the proximal leg.19
Tendon reflexes are decreased or absent in the vast majority of cases.19
MMN presents as slowly progressive weakness without sensory loss, with asymmetric involvement of two or more nerves and absence of upper motor neuron signs. Common signs and symptoms include: General fatigue, prominent muscle cramping and fasciculation, conduction blocks. The lack of sensory involvement with MMN is one of its distinguishing features. MMN affects predominantly the upper limbs, lacks bulbar or respiratory involvement and the muscle weakness is associated with little atrophy.19
MMN is characterized by motor nerve dysfunction and weakness which might be caused by demyelinating and axonal injury. In more than 50% of MMN patients, antibodies against gangliosides including GM1 are present. Antibodies (IgM) may bind to GM1 and may activate the complement cascade pathway leading to dysfunction of ion channels in peripheral nerve fibers, which leads to conduction block. The resultant progressive axonal damage may lead to progressive axonal loss and permanent disability.
The treatment options for people with MMN are limited. In contrast to the response in CIDP, MMN usually does not respond to steroids or plasma exchange and patients may worsen when they receive these treatments.20 So far, only human immunoglobulins such as octagam®, have been consistently effective.21,22,23
Diagnosis of MMN
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
Treatment of MMN
The EFNS and the PNS recommend intravenous immunoglobulin as the core initial and long-term treatment for MMN.18,20
Octagam® for MMN: A summary
for tolerability: Only 7 out of 18 patients who were treated with octagam® showed adverse events possibly related to the treatment.24
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).24
1. Frenzel W, et al. Tolerability and safety of octagam® (IVIG): a post-authorization safety analysis of four non-interventional phase IV trials. Int J Clin Pharmacol Ther. 2016;54(11):847-855.
2. Debes A, et al. Tolerability and safety of the intravenous immunoglobulin octagam®: a 10-year prospective observational study. Pharmacoepidemiol Drug Saf. 2007;16(9):1038-1047.
3. octagam®5%. Summary of Product Characteristics. May 2021.
4. octagam®10%. Summary of Product Characteristics. May 2021.
11. Gorson KC. An update on the management of chronic inflammatory demyelinating polyneuropathy. Ther Adv Neurol Disord. 2012;5(6):359-373.
12. Van den Bergh PY, et al. European Federation of Neurological Societies/Peripheral Nerve Society guideline on management of chronic inflammatory demyelinating polyradiculoneuropathy: report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society - first revision. Eur J Neurol. 2010;17(3):356-363.
13. Mathey EK, et al. Chronic inflammatory demyelinating polyradiculoneuropathy: from pathology to phenotype. J Neurol Neurosurg Psychiatry. 2015;86(9):973-985.
14. Belmokhtar C, et al. Efficacy and Safety of Octagam in Patients With Chronic Inflammatory Demyelinating Polyneuropathy. Neurol Ther https://doi.org/10.1007/s40120-019-0132-5, 2019.
15. https://emedicine.medscape.com/article/1174021-overview#a5. Sasa Zivkovic, Michael C Isfort, Multifocal Motor Neuropathy with Conduction Blocks. Updated: Nov 12, 2018.
16. Lawson VH and Arnold DW. Multifocal motor neuropathy: a review of pathogenesis, diagnosis, and treatment. Neuropsychiatric Disease and Treatment 2014:10 567-576.
17. Dimachkie MM, et al. Multifocal motor neuropathy, multifocal aquired demyelinating sensory and motor neuropathy, and other chronic aquired demyelinating polyneuropahty variants. Neurol Clin. 2013 May;31(2):533-555.
18. Beadon K, et al. Multifocal motor neuropathy. Curr Opin Neurol 2018, 31:559–564.
19. Cats EA, et al. Correlates of outcome and response to IVIg in 88 patients with multifocal motor neuropathy. Neurology. 2010 Aug 31. 75(9):818-825.
20. Van Schaik I.N. and Joint Task Force of the EFNS and the PNS. EFNS/PNS MMN GUIDELINE. European Federation of Neurological Societies/Peripheral Nerve Society Guideline on management of multifocal motor neuropathy. Report of a Joint Task Force of the European Federation of Neurological Societies and the Peripheral Nerve Society – first revision. Jl of the Peripheral Nervous System 15:295–301 (2010).
21. Vucic S, et al. Multifocal motor neuropathy: decrease in conduction blocks and reinnervation with long-term IVIg. Neurology. 2004 Oct 12. 63(7):1264-1269.
22. Van den Berg-Vos RM, et al. Multifocal motor neuropathy: long-term clinical and electrophysiological assessment of intravenous immunoglobulin maintenance treatment. Brain. 2002 Aug. 125(Pt 8):1875-1886.
23. Hahn A, et al. A controlled trial of intravenous immunoglobulin in multifocal motor neuropathy. J Peripher Nerv Syst. 2013;18:321-330.
24. 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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