Clinical Picture of MMN
Clinical criteria |
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1. Slow or stepwise progressive limb weakness |
2. Asymmetrical limb weakness |
3. Fewer than 7 affected limb regions (upper/lower arm, upper/lower leg on both sides, maximum 8) |
4. Tendon reflexes in affected limbs are decreased or absent |
5. Signs and symptoms are more pronounced in arms than in legs |
6. Age 20-65 years at onset of disease |
7. No objective sensory abnormalities except for vibration sense |
8. No bulbar signs or symptoms |
9. No upper motor neuron features |
10. No other neuropathies |
Laboratory criteria |
1. CSF protein <1 g/L |
2. High anti-GM1 IgM titer |
3. High signal intensity on T2-weighted MRI of the brachial plexus |
Electrodiagnostic criteria |
1. Definite motor conduction block: CMAP area reduction on proximal versus distal stimulation of at least 50% over a long segment (between erb and axilla, upper arm, lower arm, lower leg), or a CMAP amplitude reduction on proximal versus distal stimulation of at least 30% over a short distance (2.5 cm) detected by inching. CMAP amplitude on stimulation of the distal part of the segment with motor conduction block of at least 1 mV |
2. Probable motor conduction block: CMAP amplitude reduction on proximal versus distal stimulation of at least 30% over a long segment of an arm nerve. CMAP amplitude on stimulation of the distal part of the segment with motor conduction block of at least 1 mV |
3. Slowing of conduction compatible with demyelination: MCV 75% of the lower limit of normal; DML or shortest F wave latency 130% of the upper limit of normal or absence of F waves all after 16-20 stimuli. CMAP amplitude on distal stimulation of at least 0.5 mV |
4. Normal sensory nerve conduction in arm segments with motor conduction block. Normal SNAP amplitudes on distal stimulation |
Definite MMN |
1-11 on clinical criteria, 1 on laboratory criteria, 1 and 4 on electrodiagnostic criteria |
Probable MMN |
1-3 and 6-11 on clinical criteria, 1 on laboratory criteria, 2 and 4 on electrodiagnostic criteria |
Possible MMN |
1 and 7-11 on clinical criteria, 2 or 3 on laboratory criteria, 3 and 4 on electrodiagnostic criteria |