Brain lesions associated with abnormal muscle tone during the swing phase in post-stroke hemiparesis.

BACKGROUND: Post-stroke spasticity may involve dynamic abnormalities that impair voluntary movement, such as muscle co-contraction during gait, which may be present even in patients without apparent spasticity at rest. This study aimed to identify brain lesion locations associated with abnormal lower-limb muscle co-contraction during walking using support vector regression lesion-symptom mapping. METHODS: Thirty-two ambulatory patients with first-ever supratentorial stroke were included. Lower-limb motor impairment was defined as a Fugl-Meyer Assessment lower-extremity score of < 34. Surface electromyography recorded activity of the tibialis anterior and medial gastrocnemius muscles during gait. The co-activation index (CoI) was calculated from the overlap of normalized electromyography waveforms during the swing phase. Lesions were delineated on magnetic resonance imaging and analyzed using support vector regression lesion-symptom mapping, followed by disconnectome analysis to identify involved white matter tracts. RESULTS: A higher CoI was associated with lesions in the premotor cortex, precentral gyrus, and superior longitudinal fasciculus, with a 100% probability of disconnection in the second and third branches of the superior longitudinal fasciculus. CONCLUSION: Lesions in regions involved in sensorimotor integration were associated with abnormal lower-limb muscle co-contraction during walking, supporting the importance of dynamic gait assessment and targeted rehabilitation after stroke.