Hemichorea is the most frequent PSMD. Patients with hemichorea continually exhibit involuntary and irregular movements, which could increase morbidity through injury and extend recovery of motor function and ability of daily living [5, 6]. Pharmacological therapy, such as antidopaminergic and dopamine-depleting agents, may be effective in some cases, but drug-induced parkinsonism and tardive dyskinesia are unavoidable [7, 8]. Although hemichorea may improve with medical therapy, in certain circumstances patients could suffer from persistent and refractory symptoms. It was reported hemichorea arising from cortical stroke has a better prognosis due to integrity of deep structures circuity . In this case, the lesion was observed in the caudate nucleus—the most common location involved in persistent hemichorea symptoms [1, 10]. The medication was not effective in this patient considering that after taking tiapride hydrochloride for 2 weeks, hemichorea was not alleviated.
The pathophysiology remains uncertain. Movement disorders caused by stroke are often associated with the lesions of the basal ganglia. The basal ganglia plays an important role in generating movement; it receives signals from the cerebral cortex and sends output to the cerebellum and spinal cord through the thalamus . The neurocircuits projected by the basal ganglia to the cerebral cortex include direct and indirect pathways. When the cerebral cortex is excited, the direct pathway increases the thalamic activity, while the indirect pathway decreases the thalamic activity, the excessive inhibition of the indirect pathway will cause chorea. rTMS can inhibit the excitability of the cerebral cortex and reduce the thalamic which alleviated the symptoms of chorea. Besides, low-frequency rTMS could significantly shorter cortical silent periods (CSPs) on the M1, which is related to cortical hyper-excitability .
In this patient, 1 Hz rTMS was adopted over the left M1. After the first week of rTMS therapy, the symptoms were significantly reduced, and the frequency and intensity of involuntary movements reduced; this indicated that rTMS can have a quick effect and rapidly inhibit the excitability of the cerebral cortex. After 4 weeks, the frequency of involuntary movements decreased significantly, with no significant movements occurring during sleep. The patient was discharged with mild symptoms after 4 weeks of stimulation and rehabilitation therapy. The choreatic movements disappeared at 1-year follow-up, and the anti-choreaic drug was discontinued. which indicated that the therapeutic effect of rTMS was time-cumulative and that the excitation–inhibition balance between direct and indirect pathways was re-established to reach the optimal state. The patient was discharged after 4 weeks with only slight involuntary movement and was able to perform most of daily activities, the choreatic movements disappeared at 1-year follow-up, and the anti-choreaic drug was discontinued. These findings suggested that the efficacy of rTMS in the patient was sustained, and the biological effects were sustained for some time after the stimulation.
In this report, we used a parabolic coil instead of the figure-8 coil. The figure-8 coil is more focused, so it can only stimulate the superficial cortical regions just under the coil; in contrast, according to the designer, the parabolic coil can stimulate deeper and wider areas (supplemental Fig. 1). Evidence showed that most movement disorders result from a network dysfunction, not from a single lesion, and both M1 and SMA are closely related to hyperkinetic movement disorders. Therefore, in this study, a parabolic coil was adopted over the left M1, which could stimulate the SMA at the same time to enhance the therapeutic effect. The parabolic coil was often used peripherally to improve swallowing and respiratory and motor function after stroke [13–15]. However, to our knowledge, this is the first description of post-stroke hemichorea treated with rTMS by a parabolic coil. We also hope to stimulate deeper structures such as basal ganglia, which would have a direct effect. However, further research is needed to prove whether rTMS can stimulate subcortical gray matter directly. The outcomes observed in this patient suggest that the combination of rTMS and rehabilitation therapy may be a safe and viable strategy for PSH as an alternative to the invasive DBS method.