Neurophysiological basis of functional movement disorders: A transcranial magnetic stimulation study

The neurophysiological abnormality in patients with functional movement disorders (FMDs) is not clear. We aimed to study the neurophysiological abnormality in these patients using transcranial magnetic stimulation (TMS).

We enrolled 30 patients with FMD and 31 healthy controls (HC) in the study. Basic demographic and clinical details were recorded. The severity of motor symptoms was evaluated using the Psychogenic (Functional) Movement Disorder (PMD) Scale. The hospital Anxiety and depression rating scale (HADS) was used for assessing anxiety and depression. The motor cortex contralateral to the affected side was stimulated using a figure-of-eight coil connected to a Magstim 200² stimulator, and motor evoked potential was recorded from the first dorsal interossei muscle. The parameters recorded included resting motor threshold (RMT), central motor conduction time (CMCT), contralateral silent period (cSP), short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF).

The mean age of the patients (30.96 ± 14.02 years) was comparable to that of healthy controls (33.35 ± 9.04 years). Functional tremor (FT) was the most common phenomenology observed (50%), followed by dystonia (26.6%) and myoclonus (10%). There was a significant reduction in ICF in patients with FMD compared to HC. Also, in patients with FT, ICF was significantly reduced (0.21 ± 0.2) compared to HC (1.25 ± 0.22, p < 0.001). The SICI did not differ between patients (0.25 ± 0.23) and HC (0.34 ± 0.23, p = 0.13). No significant correlation was found between PMD score, HADS score and the TMS parameters.

Patients with FMD have reduced ICF, suggesting an abnormality in the glutamatergic neurotransmission.