Impaired intracortical inhibition in functional gait disorders: a pilot study

Abstract INTRODUCTION: Functional gait disorders (FGDs) are characterized by disabling gait and balance impairments, which lead to a significant decline in quality of life. Although recent studies have revealed some neural correlates in functional movement disorders, the findings remain inconsistent and are poorly understood. AIMS: This study aimed to explore the role of cortical inhibitory and excitatory mechanisms in the pathophysiology of FGDs using standard transcranial magnetic stimulation (TMS) paradigms. METHODS: Five patients diagnosed with FGDs based on the Fahn and Williams criteria and 15 age- and sex-matched healthy controls were recruited from neurology and psychiatry outpatient services. Cortical excitability was assessed by recording motor evoked potentials via surface electromyography from the first dorsal interosseous muscle of the dominant hand following TMS to the contralateral motor cortex. Short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated using a paired-pulse protocol, with conditioning stimuli at 80% of the resting motor threshold (RMT) and test stimuli at 120% RMT, using interstimulus intervals of 3 ms for SICI and 10 ms for ICF. RESULTS: Patients with FGDs exhibited significantly reduced cortical inhibition compared to healthy controls, as indicated by attenuated SICI responses (116 ± 66% vs. 44 ± 27%, p = 0.045). No significant differences were observed in RMT or ICF between the two groups (p = 1.000 and 0.735, respectively). CONCLUSION: These findings suggest a disruption in intracortical inhibitory mechanisms in patients with FGDs, potentially contributing to their motor symptoms. Such alterations may reflect underlying neurophysiological abnormalities associated with FGDs.