RESPONSES OF MASSETER MUSCLES TO TRANSCRANIAL MAGNETIC STIMULATION INPATIENTS WITH AMYOTROPHIC-LATERAL-SCLEROSIS

We recorded motor responses evoked by transcranial magnetic stimulatio n (TMS) in the masseter muscles of 30 patients with amyotrophic latera l sclerosis (ALS), 10 patients with cervical spondylotic myelopathy (C SM) and 22 age-matched normal controls. Responses to direct activation of the trigeminal motor root (R-MEPs) were normal both in ALS and CSM patients. Responses to activation of cortico-bulbar descending fibers (C-MEPs) were absent or delayed in 19 ALS patients (63.3%). Abnormali ties of masseter C-MEPs were more frequent than abnormalities of limb MEPs and could be observed both in patients with (77.8%) and without ( 41.7%) clinical bulbar signs. Masseter C-MEPs were normal in all CSM p atients. Recording masseter responses to TMS can reveal the frequent i mpairment of cortico-bulbar projections in ALS and can be useful in th e differential diagnosis of spinal cord compression disorders mimickin g ALS because of combination of upper and lower motor neuron signs. (C ) 1998 Elsevier Science Ireland Ltd. Ail rights reserved.