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Multifocal Motor Neuropathy (MMN)

Asymmetric Motor Neuropathy with Conduction Block

Written by: Saygı Hospital Health Guide Editorial Board
Last updated:

This content has been compiled by the Saygı Hospital Health Guide Editorial Board and is periodically reviewed by a specialist physician.

This content is for informational purposes only and does not constitute medical advice. You can book an appointment at our Nöroloji department. Book Appointment →

What is Multifocal Motor Neuropathy (MMN)?

Multifocal motor neuropathy (MMN) is a rare, treatable, immune-mediated, chronic, slowly progressive demyelinating neuropathy that selectively affects motor nerves, sparing sensory function.

Pathologically associated with anti-GM1 IgM antibodies in 30–80% of patients, suggesting autoimmune attack on motor nerve gangliosides; nodal and paranodal demyelination produces conduction block.

Hallmark electrophysiologic finding is partial motor conduction block at non-compressible nerve segments, often in the upper limbs; nerve conduction studies and ultrasound assist diagnosis.

Distinct from amyotrophic lateral sclerosis (no upper motor neuron signs, intact sensation, conduction block on NCS) and chronic inflammatory demyelinating polyneuropathy (CIDP) (which involves sensory nerves).

Symptoms

Asymmetric, slowly progressive distal weakness, predominantly affecting upper limbs (wrist drop, finger weakness, foot drop in some)
Distribution typically follows individual peripheral nerves rather than nerve roots
No sensory loss or pain; preserved deep tendon reflexes early but lost in affected territories late
Atrophy and fasciculations in chronic untreated disease
Cramps and muscle stiffness reported by some patients
Functional impact: difficulty with fine motor tasks (buttoning, writing, picking small objects), foot drop affecting gait

Risk Factors

Adults aged 20–60 years (peak in fourth and fifth decades)
Male predominance (male-to-female ratio 2:1 to 3:1)
Anti-GM1 IgM antibodies present in 30–80%
No identified environmental or genetic predisposing factors clearly established
Sporadic disease without family history typically
Possible association with prior infection in some cases (poorly defined)

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Slowly progressive asymmetric weakness in arms or legs without sensory loss
  • Wrist drop, foot drop, or weakness in distribution of individual peripheral nerves
  • Family member or self with motor neuron disease — comprehensive evaluation to rule out treatable mimics
  • Known MMN with worsening weakness, breakthrough symptoms, or treatment side effects
  • Functional decline despite ongoing therapy

Treatment Methods

01
Intravenous immunoglobulin (IVIG) is the first-line and most effective therapy: induction 2 g/kg over 2–5 days, followed by maintenance 1 g/kg every 2–6 weeks tailored to clinical response
02
Subcutaneous immunoglobulin (SCIG) as alternative or replacement maintenance for selected patients with stable disease
03
Cyclophosphamide IV pulse therapy (1 g/m² monthly for 6 months) considered for patients refractory to IVIG; risk-benefit limits long-term use
04
Rituximab 1 g IV ×2 doses or 375 mg/m² weekly ×4 in refractory cases — anecdotal benefit, ongoing trials
05
Corticosteroids and plasmapheresis are NOT effective in MMN and may worsen disease — important to distinguish from CIDP
06
Monitoring: physical examination at each visit, muscle strength testing (MRC scale), grip strength, functional scales (ONLS, INCAT), and nerve conduction studies at intervals
07
Multidisciplinary care: physical and occupational therapy, orthotics for foot drop, adaptive equipment for upper limb weakness
08
Patient education: importance of long-term IVIG maintenance, monitoring for adverse effects (headache, thromboembolism, renal dysfunction), and lifestyle adaptations

Which Department to Visit?

You can visit our Nöroloji department for these complaints. Our specialist physicians will create the most suitable treatment plan for you.

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.