Motor root conduction in neuralgic amyotrophy: evidence of proximal conduction block.

OBJECTIVE To determine the presence and role of proximal conduction block in neuralgic amyotrophy. METHODS Percutaneous electrical stimulation of cervical roots and brachial plexus was employed in eight patients with neuralgic amyotrophy. Root to Erb's point compound muscle action potential amplitude ratios for abductor digiti minimi, extensor digitorum communis, biceps, and deltoid muscles were compared with results obtained from 10 healthy controls. RESULTS Conduction block in the nerve to one muscle was found in three of eight patients (38%) suggesting focal proximal demyelination. Repeat studies showed axonal degeneration, resolution, and persistence of conduction block in these three patients respectively. CONCLUSION Focal conduction block plays a significant part in the pathogenesis of neuralgic amyotrophy, which is generally regarded as an axon loss process. Therapeutic intervention should be directed to patients with persistent conduction block, with the aim of eradicating the block and possibly minimising subsequent axon loss.