Inferential Statistics for Electrophysiological Analysis of Paretic Upper Limb-sensory Deficits and Muscle Imbalance in Patients with Acute Stroke.

Objectives: The prevalence of somatosensory dysfunction after stroke exceeds 50%, and its severity is negatively correlated with upper limb function and the ability to perform self-care tasks. This study objectively assessed somatosensory deficits in the acute post-stroke phase and characterized muscle-output imbalance across severity levels. Methods: This prospective observational pilot study was conducted at Saitama Medical University International Medical Center between June 2021 and July 2023. Forty-one patients (age 66 ± 10 years) with acute stroke were assessed for somatosensory deficits and muscle-output imbalance. The severity of somatosensory disturbance was grouped according to short-latency sensory evoked potentials (SSEP), and the change in the muscle co-contraction index (CCI) from surface electromyography (sEMG) was compared at two points within 1 week. The sEMG data for each SSEP group were replicated 1000 times using the bootstrap method. Results: An interaction was observed across all movement directions. In the comparison analysis, significant changes were observed in the normal group except for elbow flexion on the non-paretic side. In the delayed group, only wrist flexion on the non-paretic side changed more than one standard deviation. The changes observed in the severe SSEP group were inferred as fluctuations in CCI, even in the early stages of stroke onset. Conclusions: This study showed that changes in CCI of the upper extremity vary with the severity of somatosensory disturbance in patients with acute stroke and that muscle-output imbalance can change within 1 week of onset of acute stroke.