Modulation of action tremor by repetitive transcranial magnetic stimulation in multiple sclerosis patients

Background: Patients affected by Multiple Sclerosis (MS) can show a tremor of their upper limbs, mostly during the performing of finalised action (action tremor) or at the maintaining of a position against gravity (postural tremor), as key clinical feature of their disease. Objectives: In order to reduce the tremor, patients underwent to repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex of left hemisphere. Methods: Eight patients affected by a middle form of MS were enrolled into the study. A standard neurological examination was carried out and the individual degree of disability was established employing the Expanded Disability Status Score (EDSS). At EDSS patients scored from 1.5 to 6.5, mean 4.6 ±1.9 SD. Tremor was rated according to the Fahn-Tolosa Marin Rating Scale. rTMS was delivered at 1 Hz frequency, along ten subsequent, separate sessions lasting ten minutes each one (i.e. 600 pulses). All subjects were aware about the aim of the study and fulfilled a formal consent. They were free to interrupt the study at any time. Before the first session, at the fifth day and at the last day of stimulation, kinematics of upper limb movements were recorded. Patients were asked to perform a continuous pointing, moving back and forth, as fast as possible, their right index finger between two black spots depicted on a working table, placed 15 cm apart. Task lasted six minutes divided in six parts, lasting one minute each one, divided by a resting period of 30 sec. Movements were recorded by means of a optoelectronic device (ELITE system) working at the sampling rate of 100 Hz. At the end of the last session a new clinical assessment was carried out. Results: Movement time, peak of velocity and acceleration and deceleration were analysed. Number of peaks of deceleration during the targeting phase was considered as the key marker of the tremor. Results of kinematics showed an overall improvement of symptoms including a decrease of time of movement execution and time of the deceleration phase as consequence of the reduction of number of peak of deceleration (i.e. tremor). Conclusions: Reduction of tremor became apparent at the clinical evaluation. Moreover, tremor was effectively influenced by rTMS and patients reported a subjective improvement of their symptoms. We concluded that this technique could be useful in order to reduce disability in MS patients.