Electromyography of sternocleidomastoid muscle in ALS: a prospective study

Abstract

Needle electromyography (EMG) of the tongue is difficult to perform because of frequent uncontrollable movement. We chose the sternocleidomastoid (SCM) muscle as a possible alternative for assessing the involvement of the rostral neuraxis in amyotrophic lateral sclerosis (ALS). We prospectively studied 21 ALS patients during our initial diagnostic evaluation. EMG parameters that we recorded included the presence of abnormal spontaneous activity, pattern of motor unit potential recruitment, and configuration of motor unit action potentials. For the six patients with bulbar-onset ALS, three had abnormalities in the SCM and three had abnormalities in the tongue. In contrast, for the 15 patients with limb-onset ALS, 9 had abnormalities in the SCM, and only 3 had abnormalities in the tongue. Our results demonstrate the utility of needle EMG of the SCM in the evaluation of ALS. EMG of the SCM carries a similar sensitivity as the tongue in ALS patients with bulbar symptoms, but is more sensitive than the tongue in patients without bulbar symptoms. SCM innervation includes the rostral cervical cord and brainstem, and EMG abnormalities in this muscle support a diffuse involvement, which is unique to ALS.