1. Introduction

Focal hand dystonia (FHD) is a neurologic condition that affects abnormal hand muscle contractions, leading to movement disorder or posture disorder [1, 2]. FHD often manifests as focal task-specific dystonia (TSFD), a condition performing uncontrolled activation of muscle groups associated with specific, frequently overpracticed tasks, which would affect daily life and professional career [3]. It can be classified as writers’ dystonia and musicians’ dystonia [4]. Although the prevalence of FHD was relatively low which was about 8–9 per 100,000 individuals, it could have a significant impact on the professional career of writers and musicians, placing significant physical and psychological burdens on patients [5–8].

FHD treatment includes oral medications, botulinum toxin, and surgery [9]. Botulinum toxin was reported to be effective in 70% of patients with FHD [10]. However, botulinum toxin is often limited by hypotonia of the muscle spindle, and lesion surgery and DBS are choices for refractory FHD [9, 11–15]. In recent years, some neurosurgeons have used lesion surgery to treat refractory FHD and have achieved quite good therapeutic effects, especially thalamotomy [16–30]. Seven patients with writer’s dystonia having difficulty in performance received ventrooralis (Vo) thalamotomy, and all patients had a significant reduction in dystonia symptoms persistently [18]. A study consisting of 171 consecutive patients with TSFD who underwent Vo thalamotomy yielded similar results [23]. Nevertheless, apart from a review that briefly summarized thalamotomy for FHD, no detailed description of the systematic review was retrieved to provide a detailed description of thalamotomy for FHD [9]. Therefore, we performed this systematic review to assess the efficacy and safety of thalamotomy in patients with FHD.

2. Materials and Method

3. Results

3.1. Search Selection

A total of 248 studies were yielded through search databases (PubMed: 143, Embase: 68, Medline: 37). After removing duplicates, 179 articles remained. When screening titles and abstracts, 146 papers did not satisfy the inclusion criteria. After screening full texts of 33 remaining articles, 18 studies that met the exclusion criteria above have been deleted: eight reported the content of the letter, conference, or review; four did not describe hand dystonia or thalamotomy; three summarized the secondary dystonia; and three did not contain interesting data. Finally, 15 studies met the inclusion criteria and were included in the systematic review (Figure 1).

4. Discussion

This systematic review evaluated the efficacy and safety of thalamotomy for hand dystonia. Our results showed that thalamotomy could alleviate hand dystonia disability and improve hand motor function to varying degrees. Although our study suggested that thalamotomy was associated with varying degrees of complications, most were transient compared to a few permanent complications. Our research mainly included case series and case reports but lacked randomized controlled studies, so our study had a certain risk of bias. Therefore, we conducted a systematic review instead of a meta-analysis.

Bilateral pallidotomy has been reported in other studies of lesional surgery for dystonia. In a systematic review of bilateral pallidotomy for dystonia, 96% of patients showed improvement in the Burke–Fahn–Marsden Dystonia Rating Scale (BFMDRS), and 15 of 21 patients showed improvement in disability scores [31]. In another article concerning pallidotomy for primary dystonia, unilateral pallidotomy had significant improvement in the BFMDRS scores from 11.2 preoperatively to 5.4 at the last follow-up (51.8% improvement) when 14.6 preoperatively to 3.8 at the last follow-up (74.0% improvement) for bilateral pallidotomy [32]. In our study, 254 patients with FHD had varying degrees of symptom improvement after thalamotomy. The patient’s hand dystonia disability showed significant improvement after surgery using the CRS, WMS, and SSS scales, and the hand’s motor performance ability went from cessation of performance preoperatively to normal performance postoperatively using the TMDS and TSFD scales. These results demonstrate the efficacy of lesional surgery for FHD.

The mechanism of thalamotomy for FHD is currently unclear. Some scholars speculated that the reorganization of structural connections such as the cerebellum, thalamus, basal ganglia, parietal lobe, and cingulate cortex areas leads to destructive changes in sensorimotor, resulting in FHD [33–35]. In particular, changes in sensory perception in the supplementary motor area (SMAp) may explain abnormal contraction of antagonist muscles and abnormal posture [36]. Functional connections were weakened in the left lateral premotor cortex, left thalamus, and left/right pallidum through fMRI, suggesting extensive changes in the basal ganglia thalamic cortical motor circuit [37–39]. Furthermore, the changes in these circuits may be due to abnormal time windows altering the action selection process [40]. Thalamotomy may have damaging effects on these circuits, thereby improving FHD. Therefore, neurosurgeons always seem to use the thalamus as a target for FHD treatment rather than other targets due to the corticobasal ganglia-thalamo-cortical circuit [23].

In our study, 55 of 254 patients (21.7%) experienced transient or permanent complications. Nine patients (3.5%) had permanent complications including dysarthria, foot weakness, hand dysesthesia, verbal recall disturbance, and hemiparesis. Although the incidence of complications is relatively high, the incidence of permanent complications is relatively low. The result is similar to the complications of other lesion surgeries. Complications were reported in 20 of 100 patients, of which eight were permanent adverse events [31]. For ICH, a retrospective study, analyzing 721 procedures for movement disorders, reported an overall ICH rate of 5.1%, with symptomatic ICH occurring in only 1.1% of cases. For Vo thalamotomy specifically, the symptomatic ICH rate was 1.3%, and the prolonged deficit rate was 0.4% [41]. Overall, lesion surgery is relatively safe, but lesion surgery must be performed with caution to further reduce the probability of these complications.

Recurrence, defined as the deterioration of FHD scales after transient improvement, is also receiving increasing attention, as it directly affects clinical efficacy. Due to insufficient or incorrect coagulation, some patients with recurrence have significant therapeutic effects after the second thalamotomy. One article analyzing 171 patients reported 18 patients who experienced recurrence and 9 underwent a second thalamotomy of which 7 achieved improvement [23]. Other cases have also shown the same results [16, 22, 25, 29, 30]. The location and range of the target, as well as the thermocoagulation, have a significant impact on recurrence, so a careful surgical plan must be developed preoperatively.

In recent years, more and more neurosurgeons have been paying attention to deep brain stimulation (DBS) to treat dystonia. In a systematic review containing 35 articles, authors analyzed 319 patients who received pallidus internus (GPi)–DBS and 113 patients who received subthalamic nucleus (STN)–DBS. Results showed that both GPi and STN stimulation improved dystonia to varying degrees (standardized mean difference = 1.56 for GPi-DBS and standardized mean difference = 2.06 for STN-DBS) [42]. Similar results were seen with DBS for Meige syndrome [43]. One hundred and eighty-eight patients with Meige syndrome received GPi-DBS, and 110 received STN-DBS. In BFMDRS-M, the mean difference was 10.57 for GPi-DBS and 8.59 for STN-DBS. Besides, in BFMDRS-D, the mean difference was 5.96 for GPi-DBS and 4.71 for STN-DBS. However, there is no systematic evidence in the current literature to clarify the efficacy and safety of DBS treatment for FHD [44–47]. Furthermore, while DBS is reversible therapeutics, its long-term feasibility must also be considered. Since FHD often manifests at a relatively young age, typically in the 40s, factors such as device-related complications, long-term management, battery replacements, and costs highlight the importance of thalamotomy as a crucial treatment option [44].

Our study has several limitations. The major limitation is that only case series and case reports were available for inclusion in our study, which inevitably led to high positive results and publication bias. More randomized controlled trials with large samples are required to support the results. In addition, different assessment methods were used in different studies, and some assessment methods are highly subjective, which might lead to bias. A detailed and standardized scoring tool was recommended for evaluating FHD.

In conclusion, based on this systematic review, thalamotomy is an alternative option for FHD. Thalamotomy can alleviate hand dystonia disability and improve hand motor function. Thalamotomy has certain complications and it needs to be fully evaluated before surgery to ensure safety.

Conflicts of Interest

The authors declare no conflicts of interest.

Author Contributions

W.W. raised the manuscript and managed the trial. R.Y. searched the database, performed data extraction, and drafted the manuscript. B.X. searched the database, performed data extraction, and revised the manuscript. X.S. did data analysis and prepared table. X.H. prepared figures and revised the manuscript. R.Y. and B.X. contribute equally to this work.

Funding

This work was supported by 135 Project of Outstanding Development of West China Hospital, Sichuan University (ZY2017307).