Reduced intracortical inhibition and enhanced intracortical facilitation in patients with functional tremor

The pathophysiological mechanism underlying functional tremor (FT) has not been elucidated. Transcranial magnetic stimulation (TMS) is a non-invasive tool to explore cortical excitability in various neurological and neuropsychiatric disorders. The aim of this study is to evaluate the changes in cortical excitability in FT and to assess the relationship between cortical excitability and tremor severity.

This study recruited 39 patients with FT and 40 healthy controls (HCs). The clinical characteristics of the patients with FT were assessed using the Simplified Functional Movement Disorders Rating Scale (SFMDRS), Clinical Global Impression Severity Scale, and Symptom Check List-90. Intracortical excitability was assessed, including short/long-interval intracortical inhibition (SICI/LICI) and intracortical facilitation (ICF), in all participants using paired-pulse TMS.

Compared with HCs, patients with FT exhibited reduced SICI-2 ms and SICI-4 ms and enhanced ICF-10 ms. Interhemispheric comparisons showed unbalanced excitability with reduced SICI-2 ms, increased ICF-8 ms and increased ICF-10 ms in the more affected side, which were not observed in HCs. The correlation analysis showed that SFMDRS scores were positively correlated with the Hamilton Anxiety Rating Scale and SICI-2 ms.

The findings indicate altered cortical excitability in patients with FT. Reduced intracortical inhibition was correlated with tremor severity, suggesting impaired inhibitory pathways in patients with FT.

ChiCTR2200066389; Chinese Clinical Trial Registry.