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

Objective-To determine the presence and role of proximal conduction block i n neuralgic amyotrophy. Methods-Percutaneous electrical stimulation of cervical roots and brachial plexus was employed in eight patients with neuralgic amyotrophy. Root to Er b's point compound muscle action potential amplitude ratios for abductor di giti 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 e ight patients (38%) suggesting focal proximal demyelination. Repeat studies showed axonal degeneration, resolution, and persistence of conduction bloc k in these three patients respectively. Conclusion-Focal conduction block plays a significant part in the pathogene sis of neuralgic amyotrophy, which is generally regarded as an axon loss pr ocess. Therapeutic intervention should be directed to patients with persist ent conduction block, with the aim of eradicating the block and possibly mi nimising subsequent axon loss.