Multiple system atrophy (MSA), an orphan, adult-onset, sporadic, progressive neurodegenerative disease, is characterized by Parkinsonian features, cerebellar ataxia, and autonomic failure in various combinations (1). Early and severe autonomic failure is a core feature of MSA, including fatigue (2). Studies have shown that fatigue, an independent non-motor symptom, is one of the most common and major problems for 38–61% MSA patients, which contributes greatly to reduced social participation and quality of life (3–5). Treatment of fatigue can be very challenging, as till now there is no widely accepted treatment protocol available, including pharmacological treatment, deep brain stimulation, and rehabilitation strategies (5, 6).

Repetitive transcranial magnetic stimulation (rTMS), a potent tool and non-invasive means of electrically stimulating neurons in the cerebral cortex, is able to modify neuronal activity of targeted cortical areas and has been widely applied to treat various neurological conditions (7). Several studies have shown that rTMS could alleviate the severity of motor disability in MSA patients (8–10). To our best knowledge, however, no study has so far specifically investigated the effects of rTMS on fatigue in patients with MSA. Previous studies have demonstrated that rTMS over the left dorsolateral prefrontal cortex (DLPFC) help improve fatigue symptom in some other neurological disorders, including fibromyalgia, myalgic encephalomyelitis, and multiple sclerosis (11–14). Moreover, high-frequency rTMS with an optimal frequency of 10 Hz applied to the DLPFC has been suggested as a potent treatment for fatigue with a Level A evidence (11–14). Here, in the present study, we aimed to investigate the effect of high-frequency rTMS over the left DLPFC on fatigue in patients with MSA. We hypothesized that high-frequency rTMS over the left DLPFC can alleviate fatigue in patients with MSA.

In this randomized, double-blind, sham-controlled study, we demonstrated that high-frequency rTMS over the left DLPFC induced a short-lasting improvement in fatigue in patients with MSA. In addition, patients' motor symptoms, as well as depression and anxiety symptoms, were also shortly improved to a certain extent after the active rTMS. Though the beneficial effects lasted no more than 4 weeks, we suggest that the high-frequency rTMS over the left DLPFC could still be used as an available therapeutic protocol for alleviating fatigue in patients with MSA.

The beneficial effects of rTMS on fatigue have been previously reported in several neurological disorders, such as fibromyalgia, myalgic encephalomyelitis, and multiple sclerosis, as fatigue is a common symptom in these disorders and contributes substantially to decrements in quality of life and disability (15). A randomized-controlled trial provided evidence that 4 weeks of daily high-frequency (10 Hz) rTMS over the left DLPFC rTMS is able to improve fatigue in patients with fibromyalgia, and provided impetus that the utility rTMS may be an available approach for the relief of fatigue in related disorders (11). Another similar study investigating rTMS effect in patients with fibromyalgia revealed significant improvements in fatigue, depression, and quality of life in the rTMS treatment group when accepting daily high-frequency (10 Hz) rTMS to the left DLPFC over 3 weeks (12). Recently, Yang et al. (13) reported that rTMS over the left DLPFC improves fatigue in patients with myalgic encephalomyelitis and suggested that rTMS can be a novel therapeutic intervention for fatigue. None of the patients previously experienced serious side effects in these studies, which provide compelling evidence for the safety of rTMS treatment. These studies suggest that 10 Hz rTMS over the left DLPFC may be an effective and safe strategy to relieve fatigue in patients with chronic neurological disorders. In the present study, similarly, our findings also provided evidence for the beneficial effects of rTMS, indicating that high-frequency rTMS over the left DLPFC may be a safe and effective therapy for alleviating fatigue in patients with MSA.

It is well-known that the most common and widely used site for rTMS relieving depression is DLPFC (15–18). High-frequency rTMS over the left DLPFC has been suggested as Level A evidence (definite efficacy) for relieving depression, and as Level B evidence (probable efficacy) for improving Parkinson's disease related depression (19). Though fatigue and depression have some clinical features in common, fatigue is distinguishable from depression and indeed an independent entity from depression (20). Fatigue refers to subjective sensations of weariness, increasing sense of effort, mismatch between effort expended and actual performance, or exhaustion (20). However, fatigue and depression, both of which are common non-motor symptoms in patients with MSA, do have similar pathophysiological mechanisms, including serotonergic dysfunction in basal ganglia and limbic circuits, which contribute to dysfunction of prefrontal-basal ganglia loops and impaired integration of limbic input and motor functions (6). Although no evidence-based guidelines have been proposed on the therapeutic use of rTMS for fatigue yet (19), the left DLPFC has been chosen as the optimal stimulation target for fatigue treatment in several previous studies (11–13). Here, we used the same stimulation target and demonstrated similar favorable results. It has been generally suggested that rTMS can not only generate biological effects on the stimulation site per se, but also on other distant sites connected by the activated networks (21). High-frequency rTMS generates a remarkable change of blood-oxygen-level-dependent (BOLD) signal within large and distant areas of the cortex (22). Several studies have also proved that high-frequency rTMS of the DLPFC can increase dopamine release within basal ganglia (23, 24). Furthermore, the effects of high-frequency rTMS might be the result of not only a direct enhancement of motor cortex excitability (25), but also a decrease of inhibitory γ-aminobutyric acid (GABA) neurotransmission-mediated intracortical inhibition (26). Therefore, high-frequency rTMS over DLPFC is assumed to increase the cortex excitability and dopamine release and modulate cortical plastic, which may impart a beneficial effect on fatigue symptom.

In the present study, though we found that rTMS could improve fatigue in MSA patients, the beneficial effect lasted no more than 4 weeks. Differently, in another two randomized, placebo-controlled trials (11, 12), both studies showed long-term favorable rTMS effects on relieving fatigue in patients with fibromyalgia. Such discrepancy may be attributed to the different parameters used in our study, that is, with an intensity of 100% RMT (vs. 120% RMT in their studies), 1,200 pluses per session (vs. 3,000 pulses) and a total of 2 weeks duration (vs. 4 weeks). More importantly, MSA is characterized by a relentless worsening of motor and non-motor symptoms, with a more rapid progression at the onset (1); whereas fibromyalgia is a mild chronic disorder (11). This indicates that at the time of follow-up, patients may already experience aggravation of motor symptoms and non-motor symptoms, which may also contribute to the inconsistency.

In addition, our results showed that rTMS over left DLPFC could also improve depression and anxiety, as well as motor symptoms in patients with MSA. It is generally known that rTMS over the left DLPFC could improve depression, including Parkinson's disease-related depression (16–18). The improvements in MSA-related depression symptoms observed in our study are consistent with the results of many previous studies. Motor symptom scores were also statistically significant improvement between the two groups. As noted previously, the magnetic stimulus has distant actions, which means it not only activates local inter-neuronal circuits, but also those fibers projecting to distant structures. The distant actions of rTMS were initially demonstrated in some studies, which showed that rTMS over the DLPFC can modulated M1 excitability, even at a higher extent than direct M1 stimulation itself (15, 17). It may provide evidence that motor symptoms were improved through rTMS stimulating over the DLPFC in our study.

Our study has several limitations. First, the study was conducted in a single center and the number of participants is relatively small. Second, as the diagnosis of early MSA is full of challenge, only patients with a clear diagnosis were enrolled in our study, indicating a relatively more sever disease. Future studies with a bigger sample size enrolling more MSA patients in the early stage are warranted to clarify the rTMS effect on fatigue in MSA patients.

In conclusion, our findings suggest that high-frequency rTMS over left DLPFC may ultimately serve as an add-on therapy for alleviating fatigue in MSA patients, though the beneficial effects last no more than 4 weeks. In the future, more optimistic rTMS protocols and techniques are needed to prolong the treatment effect in routine clinical practice.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the Xuanwu Hospital Ethics Committee. The patients/participants provided their written informed consent to participate in this study.

PC, J-HM, and HS designed the study. JP carried out data collection, analyzed the data, and drafted the manuscript. PC and T-MM revised the manuscript. All authors have read and approved the final version for publication.

This work was supported by grants from the National Key R&D Program of China (Nos. 2018YFC1312001 and 2017YFC0840105), Beijing Municipal Administration of Hospitals' Mission Plan (Code: SML20150803), Beijing Municipal Science and Technology Commission (No. Z171100000117013), and Inner Mongolia Natural Science Foundation (No. 2020MS08138).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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