Amyotrophic lateral sclerosis versus cervical spondylotic myelopathy: a study using transcranial magnetic stimulation with recordings from the trapezius and limb muscles.

OBJECTIVE: We report an electrophysiological method to differentiate amyotrophic lateral sclerosis (ALS) from cervical spondylotic myelopathy (CSM).
METHODS: Motor evoked potentials (MEPs) by transcranial magnetic stimulation were investigated in patients with ALS (n=10) and CSM (n=9). In addition to limb MEPs using the triple stimulation technique (TST) at upper limbs, MEPs recorded from trapezius muscles were compared with those obtained from 23 normal subjects. The parameters studied were: central motor conduction time, amplitude ratio and, for the trapezius, the interside asymmetry.
RESULTS: Whereas limb MEPs were abnormal in most ALS and CSM patients (17/19), trapezius MEPs were abnormal in all ALS patients, and normal in 8 out of 9 CSM patients.
CONCLUSION: Recording of trapezius MEPs is a valuable addition to the limb MEPs study, since it distinguishes ALS from SCM in most patients.