Usefulness of cervical root magnetic stimulation in assessing proximal motor nerve conduction

Objectives: To evaluate the reliability and utility of cervical root magnetic stimulation in exploring proximal motor conduction. Methods: In 20 patients with demyelinating polyneuropathy (DPN), 20 patients with amyotrophic lateral sclerosis (ALS) and 25 healthy subjects, evoked compound muscle action potentials (CMAPs) were recorded from abductor digiti minimi muscle in response to electrical stimulation up to Erb's point and magnetic stimulation up to the cervical roots. Results: In all healthy and ALS subjects, magnetic root stimulation confirmed the absence of conduction abnormalities, including those in whom supramaximal responses at Erb's point were not achieved. In the DPN group, conduction block and/or temporal dispersion was revealed by magnetic root stimulation in 9 out of 20 patients (45%), 3 more than those detected at Erb's point. Conclusions: Cervical root stimulation allowed clear distinction between motor neuronopathy and DPN. It is recommended as part of the routine evaluation of patients suspected of having DPN, especially when distal nerve studies are inconclusive.