The electrophysiological study of differential diagnosis between amyotrophic lateral sclerosis and cervical spondylotic myelopathy.

Sternocleidomastoid muscle EMG (SCM-EMG) and dermatomal somatosensory evoked potential (DSSEP) were evaluated as diagnostic aids in differentiation between amyotrophic lateral sclerosis (ALS) and cervical spondylotic myelopathy (CSM) in this study. 104 inpatients were divided into three groups: those diagnosed clinically as either (A) ALS (36 cases), or (B) CSM (32 cases) and (C) those needed further investigation (36 cases). EMG of limb muscles and sternocleidomastoid of both sides in all, and of tongue muscles in 58/104 of three groups; DSSEP in 56/104 of all three groups; MRI/CTM in 12/36 of group A and all patients of group B and C. SCM-EMG abnormal in 34/36 of group A but normal in all 32 of group B. SCM-EMG also abnormal in 32/36 of group C and 8 of them showed postoperative aggravation. DSSEP normal in 12/12 of group A while abnormal in 19/20 of group B. DSSEP abnormal only in 6/24 of group C. MRI/CTM showed spinal compression in all cases presenting abnormal DSSEP and close correspondence between upper margins of pathological involvement as revealed using these two methods. Both SCM-EMG and DSSEP have proved to be valuable differential aids between ALS and CSM.