Distal Predominance of Electrodiagnostic Abnormalities in Early-Stage Amyotrophic Lateral Sclerosis

Introduction: In this study we compared the electrodiagnostic (EDX) yield of limb muscles in revealing lower motor neuron (LMN) dysfunction by electromyography (EMG) in early-stage amyotrophic lateral sclerosis (ALS). Methods: This investigation was undertaken as a retrospective review at a single center. Results: Our study included 122 consecutive patients with possible ALS, as defined by revised El Escorial criteria. Distal limb muscles showed more frequent EMG abnormalities than proximal muscles. EDX yield was found to be higher in the limb where weakness began and when clinical signs of LMN dysfunction were evident. Adoption of the Awaji criteria significantly increased the yield of EMG-positive segments in the cervical (P < 0.0005) and lumbosacral (P < 0.0001) regions, and upgraded 19 patients into the probable category and 1 patient into the definite category. Discussion: EMG abnormalities are predominant in the distal limb in early-stage ALS. A redefinition of an EDX-positive cervical or lumbosacral segment, with an emphasis on distal limb muscles, may result in an earlier ALS diagnosis. Muscle Nerve 58: 389–395, 2018.