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- Title
Cortical excitability and inhibitory phenomena in patients with functional movement disorders.
- Authors
Banerjee, Sattwika; Choudhury, Supriyo; Bayen, Asit B.; Kumar, Praveen; Naskar, Subrata; Kumar, Hrishikesh
- Abstract
Background: Functional movement disorders (FMDs) are part of neurological disorders where patients present with abnormal movements mimicking an organic movement disorder. Presence of maladaptive plasticity could be a potential risk for this group of disorders. Cortical plasticity depends on the balance between excitatory and inhibitory systems. The changes in the excitatory or inhibitory systems of human motor cortex can be evaluated noninvasively by transcranial magnetic stimulation (TMS). Aims: In this study, we explored the cortical excitability and inhibitory phenomena through standard TMS parameters like short intracortical inhibition (SICI), short latency afferent inhibition (SAI), and intracortical facilitation (ICF) in patients with FMD and compared them with the responses in healthy controls. Materials and Methods: In this cross-sectional study, we recruited patients from the movement disorder and psychiatry outpatient department. The clinical symptoms and their severity were assessed using the Psychogenic Movement Disorder Rating Scale (PMDRS). The cognition, anxiety, and depressive states were estimated using the Montreal cognitive assessment (MoCA) scale, generalized anxiety disorder rating scale (GAD-7), and patient health questionnaire (PHQ-9), respectively. Motor-evoked potentials (MEP) were estimated from the surface electromyography (EMG) responses over the first dorsal interosseous muscle of the dominant hand after application of TMS on the contralateral motor area of the scalp. The resting motor threshold (RMT) was assessed by standard methods described by Pitcher et al. in 2002. For the paired pulse paradigm (SICI, ICF), a subthreshold conditioning magnetic pulse (80% of RMT) was delivered before delivering suprathreshold test stimuli (120% of RMT). The interstimulation intervals between the test and the conditioned stimuli were 3 ms for SICI and 8 ms for SICI and ICF paradigms, respectively. For SAI paradigm, peripheral stimulation was delivered by stimulating the median nerve at the wrist. The interstimulus interval between the TMS stimulation and the nerve stimulus was 18--22 ms. Data were acquired through Spike 2 software and analyzed using custom-written MATLAB (Mathwork) code and Statistical Package for the Social Sciences (SPSS) v22 (IBM). Results and Conclusion: We recruited seven clinically diagnosed FMD patients (age 30.4 ± 12.64 years) predominantly having symptoms of tremor and gait disorders and compared them with four age-matched healthy controls (age 24.4 ± 1.5 years). The mean PMDRS score was 10.2 ± 3.6, indicating minimal to mild severity. There was a positive correlation of age with the PMDRS score (rho = 0.851, P = 0.015), indicating that with advancing age, there is increased severity, and a negative correlation with the PMDRS and MoCA scores (rho = -0.898, P = 0.038), indicating that the disease severity could alter the cognitive state. We were unable to find any significant difference in the cortical inhibition and excitation phenomena between the patients and healthy individuals. The mean SICI and ICF of FMD patients (63% and 124%, respectively) were not significantly different from those of healthy participants (70% and 133%, respectively) (P = 0.571 and 0.786, respectively). The mean SAI of FMD patients (70%) was not significantly different from that of healthy participants (91%, P = 0.393) either. This is an ongoing study and we have presented our preliminary results here. These preliminary results indicate that the deficit and the clinical symptoms are not associated with the cortical phenomena. This apparently null finding may open the avenues of including selected TMS paradigms in the initial diagnostic work-up of FMD patients.
- Subjects
MOVEMENT disorders; COGNITION; CLINICAL trials
- Publication
Annals of Movement Disorders, 2022, Vol 5, pS22
- ISSN
2590-3446
- Publication type
Abstract