Intermuscular coherence from muscle pairs in the leg as a biomarker for amyotrophic lateral sclerosis

Objective: To evaluate the diagnostic potential of intermuscular coherence (IMC) measured from leg muscle pairs as an early-stage biomarker for amyotrophic lateral sclerosis (ALS). Methods: Surface electromyography (sEMG) was recorded in neurotypical subjects and patients with early-stage ALS from muscle pairs: gastrocnemius lateralis–gastrocnemius medialis (GLGM), tibialis anterior–extensor digitorum brevis (TAED), and vastus lateralis–vastus medialis (VLVM). IMC within the 20–40 Hz range (IMCβγ) and the imaginary component of coherency in the 20–40 Hz range (ICOHβγ) were calculated. Area under the receiver operating characteristic curves (AUC) was used to assess diagnostic performance. Results: IMCβγ was lower in ALS patients than neurotypical subjects for all three muscle pairs (p < 0.05 in all cases). Diagnostic performance (AUC) ranged from 0.69 to 0.78 and was highest for TAED. Reducing the effect of volume conduction by using ICOHβγ tended to improve the diagnostic ability (AUC range 0.76 to 0.84). Conclusions: IMCβγ from leg muscles, particularly TAED, can help differentiate early-stage ALS patients from neurotypical individuals. ICOHβγ further improves diagnostic performance by reducing volume conduction artifacts. Significance: Leg muscle IMC measurements could aid in the early and accurate diagnosis of ALS.