Efficacy of Dorso-lateral Prefrontal Cortex Stimulation by tDCS in Motor Conversion Disorder Patients

Conversion disorder refers to impaired voluntary motor or sensory functions that are not compatible with a well-known neurological condition. This disorder affects up to 30% of hospitalized patients in neurology departments and symptoms persist in 35% of patients after 12 years of evolution. Despite a poor prognosis, no treatments have been validated to date. The development of non-invasive brain stimulation techniques has allowed the creation of treatments focused on dysfunctional brain regions associated with motor conversion disorder. Hypoactivation of prefrontal dorso-lateral cortex underlies the course of functional motor symptoms. Results of the HYCORE study conducted at Nîmes University Hospital (including 20 patients, clinicaltrial.gov NCT02329626) confirmed these results and related hypoactivation of PFDLC to persistent motor disability at 3 months and 6 months follow-up. Activation of the PFDLC could restore executive control and thus promote the recovery of motor symptoms. However, in most repeated Transcranial Magnetic Stimulation (rTMS) the primary motor areas were targeted and the clinical improvement was related to self-suggestion induced by the motor response produced. Among the different techniques, transcranial Direct Current Stimulation (tDCS) is a medical neuromodulation device that delivers a direct, low-intensity electric current to cortical areas, facilitating neuronal activity. Recently, PFDLC stimulation via tDCS has been used to treat several neuropsychiatric disorders and shown to be effective in depression. In addition, this technique has several advantages compared to rTMS: its use is simpler and costs 5 to 8 times less, the device is portable and there is no titration procedure. The tolerance of the tDCS is also better with no risk of epileptic seizure, neuronal depolarization being absent.