Translation of surface electromyography into a clinically applicable objective bulbar assessment tool to improve measurement-based care in amyotrophic laterals sclerosis

Objective This study aims to translate surface electromyography (sEMG) into a clinically applicable, objective tool for assessing bulbar involvement in amyotrophic lateral sclerosis (ALS). Methods A clinically grounded sEMG framework was developed, integrating a standardized, repeatable protocol with a novel analytic pipeline, to automatically extract 60 features from six craniofacial muscle groups during a set of motorically demanding but cognitively and linguistically less challenging oral diadochokinetic (DDK) tasks. Using this framework, 104 oral DDK recordings were acquired from 16 individuals with ALS—nine with overt bulbar symptoms (ALS+B) and seven without (ALS-B)—and 10 healthy controls (HCs). The sEMG features were clustered into 10 interpretable composite measures and validated by evaluating their (1) internal consistency using Cronbach’s α ; (2) associations with standardized functional outcomes and a biomechanical metric—stiffness—via mediation analysis; (3) discriminatory efficacy in distinguishing ALS+B and ALS-B from HC, as well as from each other, using machine learning classifications; and (4) robustness to common nonmotor confounders, including age, sex, and cognitive-linguistic impairments, through a comparison of discriminatory performance before and after adjustment for these factors. Results All composite measures exhibited (1) high internal consistency (Cronbach’s α = 0.89 ± 0.071 ), (2) significant (or marginally significant) direct or stiffness-mediated indirect associations with the functional outcomes, and (3) consistently high discriminatory accuracy (0.82–0.85), both before and after adjustment for confounders. Conclusion The sEMG framework demonstrates strong potential as a reliable, valid, and robust objective tool to detect subclinical neuromuscular changes throughout the prodromal and symptomatic phases of bulbar involvement in ALS, while remaining resistant against disease-related cognitive-linguistic impairments and disease-unrelated confounders. This tool may augment standard clinical evaluations, enabling earlier detection of bulbar involvement and measurement-based care in ALS.