Multifocal motor neuropathy is a rare, immune-mediated neuropathy characterized by progressive asymmetrical limb weakness without sensory deficits.
Males are more affected than females (3:1) and the mean age of onset is 40.
Presentation:
- The most common presentation is wrist drop and impaired grip strength.
- Distal muscles are affected more commonly than proximal ones
- Upper limb is more commonly affected than lower limb
- There may be fasciculations
- There may be muscle wasting
- There is no sensory involvement
- There are no upper motor neuron signs
Diagnosis
- Nerve conduction studies – show multifocal partial conduction blocks in motor but not sensory nerve fibres
- High titre IgM anti-GM1 serum antibodies – 20-80% of patients
Treatment
- IV IG improves symptoms and slows progression
- Plasma exchange/corticosteroids are not indicated and can make symptoms worse
Differential diagnoses
- Motor neurone disease
- Cervical radiculopathy
- Lyme disease
