Assessment of muscle fatigue in multiple sclerosis patients in electromyographic examinations

BACKGROUND: Although surface electromyography (sEMG) is the method used to assess muscle fatigue in patients with multiple sclerosis (PwMS), no pattern of signal change has been established. The differences shown in the parameters of other neurophysiological tests between PwMS and control groups (CG) suggest the differentiation of the sEMG signal. AIM: The purpose of the study was to verify potential differences in the fatigue sEMG signal in PwMS compared to CG. DESIGN: Cross-sectional study. SETTING: Chair and Department of Functional Diagnostics and Physical Medicine. POPULATION: A randomised group of patients diagnosed with MS (30, 20-41 years). A random sample of young, healthy adults (median 28, 20-39 years). METHODS: Measurement of sEMG was performed from extensor carpi radialis (ECR) and FCR (flexor carpi radialis) during 60-80% of maximum voluntary contraction (MVC) of extension and then flexion for 60sec, accordance with the fatigue protocol in Research XP Master Edition software (v. 1.08.27). RESULTS: Root mean square amplitude (A(RMS)) were lower for muscle in the PwMS compared to the CG (ECR P=0.0001, FCU P<0.0001). In the CG, the A(RMS) value increases during fatigue contraction (ECR P=0.0003, FCU P<0.0001), while in the PwMS) the A(RMS) value decreases (ECR: P<0.0001, FCU P<0.0001. CONCLUSIONS: The PwMS show an opposite pattern of preservation of the absolute value of A(RMS) during prolonged contraction to fatigue, compared with healthy subjects. CLINICAL REHABILITATION IMPACT: The results are important for clinical trials using sEMG to assess fatigue in PwMS. Knowledge of the differences in the time domain changes in sEMG signal between healthy subjects and PwMS is crucial for correctly interpreting the results.