Multifocal motor neuropathy with conduction block: Distribution of demyelination and axonal degeneration.
OBJECTIVE
Multifocal motor neuropathy with conduction block (MMN) is an immune-mediated neuropathy, characterized by progressive muscle weakness. Although demyelination is regarded as the underlying pathophysiologic mechanism of MMN, recently, it was reported that different pathophysiologic mechanisms were responsible for disease in the upper and lower limbs. Specifically, demyelination in the upper limbs and axonal loss in the lower limbs. Consequently, the aim of the present study was to assess, through clinical neurophysiology studies, whether different pathophysiologic mechanisms were occurring in the upper and lower extremities. Furthermore, we wanted to investigate whether the presence of conduction block (CB) correlated with axonal degeneration (AD), and to determine the electrophysiological abnormalities that correlate with muscle weakness.


METHODS
We reviewed medical records of 18 patients with MMN for clinical features (using the Medical Research Council score and Guys Neurology Disability Scale) and neurophysiologic abnormalities (CB, AD prolongation of distal motor and F-wave latencies, and reduction of conduction velocity in the demyelinating range).


RESULTS
Electrophysiological abnormalities deemed specific of demyelination were non-significantly different in the upper and lower extremities. The presence of axonal degeneration correlated significantly with conduction block (odds ratio 10.4, 95% CI 4.2-25.6), and both parameters correlated with muscle weakness (P<0.01).


CONCLUSIONS
Our study suggests that the same pathophysiologic process occurs in the upper and lower extremity nerves. Moreover, one pathophysiologic process may be responsible for the development of CB and AD, and therefore muscle weakness.


CONCLUSIONS
The present study has established that both AD and CB occur in MMN, irrespective of extremity, and both correlate with muscle weakness.
Vucic
Steve
S
Institute of Neurological Sciences, Prince of Wales Hospital, University of New South Wales, Randwick, 2035, Sydney, Australia.
Black
Kristin
K
Chong
Peter Siao Tick
PS
Cros
Didier
D
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000368:Aged; D003711:Demyelinating Diseases / Q000473:pathology / Q000503:physiopathology*; D004558:Electric Stimulation / Q000379:methods; D004594:Electrophysiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016472:Motor Neuron Disease / Q000473:pathology / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D009410:Nerve Degeneration / Q000503:physiopathology*; D009431:Neural Conduction / Q000502:physiology; D011930:Reaction Time / Q000502:physiology