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.

Clinical utility of trapezius muscle studies in the evaluation of amyotrophic lateral sclerosis

“…21,22 The innervation of the upper trapezius is not definite, but several studies show that the upper trapezius receives innervation from both the lower medulla and upper cervical cord, since the accessory nucleus lies in both segments. 6,[23][24][25] Motor evoked potential abnormalities were not found to be correlated with bulbar dysfunction severity, but the difference in the bulbar AALSRS scores between the two groups proved significant. This suggests that bulbar dysfunction is more severe in patients with an abnormal MEP.…”

“…2,3 Thus, in a recent study, SCM was used as an alternative lower cranial nerve innervated muscle for EMG in ALS. 6 In our study, to solve the electrophysiological challenges associated with recording from the lower cranial nerveinnervated muscles such as the tongue and masseter, the upper trapezius were examined as alternatives. MEP of the upper trapezius in ALS patients revealed abnormalities in 12 of 17 patients.…”

“…The findings of a previous study, which compared EMG sensitivities of the SCM and the tongue, concur with our findings. 6 The parameter analyzed in the present study was the central motor conduction time (CMCT), where CMCT abnormalities were defined as absent or delayed (>mean + 2 SD) responses. In a previous study, the MEP/CMAP amplitude ratio was used as an additional parameter to assess corticobulbar and corticospinal tract dysfunction.…”

“…The pattern of motor unit action potential morphology recruitment was excluded due to faster firing rates of the bulbar muscles. 6 …”

“…5,6 Though the number of muscles studied per patient varied, needle EMG was performed in the bulbar, limb, and paraspinal muscles. In particular, attention was focused on the tongue, SCM, and upper trapezius muscles.…”