Effects of Low-frequency Repetitive Transcranial Magnetic Stimulation on Focal Hand Dystonia: A Case Report

A 40-year-old female patient with no medical history or family history of dystonia showed no abnormalities on cranial MRI. However, flexions and extensions were poor during the right arm and elbow movements, and tremors were observed during the finger separation movement. The tremors reduced when the left hand was placed on the right shoulder. The patient was, therefore, diagnosed with right hand dystonia and treated with repetitive transcranial magnetic stimulation (rTMS) therapy. The motor cortex regulating the right arm was stimulated with a 1 Hz rTMS, performed 350-500 times at an intensity 1.2 times of that of the threshold value. When involuntary movements improved after 350 times, we measured the simple test for evaluating hand function (STEF), and finger-bending and writing movements before and after stimulation by monitoring the changes in cerebral blood flow using near-infrared spectroscopy (NIRS). We also assessed the motor evoked potential (MEP), cortical silent period (CSP), and short-interval intracortical inhibition (SICI) before TMS and after 150 times and 350 times. The arm movement was recorded as a video. After 150 stimulations of rTMS, the right arm and finger separation movements improved; after 350 stimulations, movements became very quick and comparable with those of the left side. There were clear improvements in STEF and writing. Although there was no significant change in MEP, we observed a prolonged CSP latency and a significant decrease in the SICI ratio. NIRS evaluations showed that changes in the relative concentrations of hemoglobin (Hb) in the left motor cortex regulating the right finger movement after rTMS were minimal when compared to that before rTMS; however, a significant decline was seen in the left premotor and prefrontal cortexes. A decline in the writing movement was seen in the left motor, premotor, and prefrontal cortexes. However, symptoms improved and remained stable for a long time with low-frequency rTMS. We experienced a case of upper limb dystonia where low-frequency, above-threshold rTMS on the motor cortex showed significant effects. Changes in plasticity were seen in long-term rTMS. NIRS was validated as a useful index of indirect brain function for observing the effects of rTMS.