Deep brain stimulation in dystonia: factors contributing to variability in outcome in short and long term follow-up

Deep Brain Stimulation of the Medial Forebrain Bundle for Treatment-Resistant Depression: A Systematic Review Focused on the Long-Term Antidepressive Effect

OBJECTIVE

Major depression affects millions of people worldwide and has important social and economic consequences. Since up to 30% of patients do not respond to several lines of antidepressive drugs, deep brain stimulation (DBS) has been evaluated for the management of treatment-resistant depression (TRD). The superolateral branch of the medial forebrain bundle (slMFB) appears as a "hypothesis-driven target" because of its role in the reward-seeking system, which is dysfunctional in depression. Although initial results of slMFB-DBS from open-label studies were promising and characterized by a rapid clinical response, long-term outcomes of neurostimulation for TRD deserve particular attention. Therefore, we performed a systematic review focused on the long-term outcome of slMFB-DBS.

MATERIALS AND METHODS

A literature search using Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria was conducted to identify all studies reporting changes in depression scores after one-year follow-up and beyond. Patient, disease, surgical, and outcome data were extracted for statistical analysis. The Montgomery-Åsberg Depression Rating Scale (ΔMADRS) was used as the clinical outcome, defined as percentage reduction from baseline to follow-up evaluation. Responders' and remitters' rates were also calculated.

RESULTS

From 56 studies screened for review, six studies comprising 34 patients met the inclusion criteria and were analyzed. After one year of active stimulation, ΔMADRS was 60.7% ± 4%; responders' and remitters' rates were 83.8% and 61.5%, respectively. At the last follow-up, four to five years after the implantation, ΔMADRS reached 74.7% ± 4.6%. The most common side effects were stimulation related and reversible with parameter adjustments.

CONCLUSIONS

slMFB-DBS appears to have a strong antidepressive effect that increases over the years. Nevertheless, to date, the overall number of patients receiving implantations is limited, and the slMFB-DBS surgical technique seems to have an important impact on the clinical outcome. Further multicentric studies in a larger population are needed to confirm slMFB-DBS clinical outcomes.

Pallidal deep brain stimulation for patients with myoclonus-dystonia without SGCE mutations

BACKGROUND

Pallidal deep brain stimulation (GPi-DBS) is effective for treating myoclonus and dystonia caused by SGCE mutations (DYT-SGCE, DYT11). However, it is unknown whether GPi-DBS is effective for the treatment of myoclonus-dystonia which is not associated with the SGCE gene mutations. In this study, we investigated the efficacy of GPi-DBS in treating myoclonus-dystonia in SGCE mutation-negative cases.

METHODS

Three patients with myoclonus-dystonia without SGCE mutations who underwent GPi-DBS were evaluated preoperatively and 6 months postoperatively using the Unified Myoclonus Rating Scale (UMRS) and Fahn-Marsden Dystonia Rating Scale (FMDRS) for myoclonus and dystonia, respectively. In two of the three patients, myoclonus was more evident during action. Myoclonus was predominant at rest in the other patient, and he was unaware of his dystonia symptoms. The results were compared with those of the four DYT-SGCE cases.

RESULTS

The mean UMRS score in patients with myoclonus-dystonia without SGCE mutations improved from 61.7 to 33.7 pre- and postoperatively, respectively, and the mean FMDRS score improved from 7.2 to 4.5. However, the degree of improvement in myoclonus-dystonia in patients without SGCE mutations was inferior to that in patients with DYT-SGCE (the UMRS score improved by 45% and 69%, respectively).

CONCLUSIONS

GPi-DBS is effective for treating myoclonus-dystonia in patients with and without SGCE mutations. GPi-DBS should be considered as a treatment option for myoclonus-dystonia without SGCE mutations.

Clinical neurophysiology in the treatment of movement disorders: IFCN handbook chapter

In this review, different aspects of the use of clinical neurophysiology techniques for the treatment of movement disorders are addressed. First of all, these techniques can be used to guide neuromodulation techniques or to perform therapeutic neuromodulation as such. Neuromodulation includes invasive techniques based on the surgical implantation of electrodes and a pulse generator, such as deep brain stimulation (DBS) or spinal cord stimulation (SCS) on the one hand, and non-invasive techniques aimed at modulating or even lesioning neural structures by transcranial application. Movement disorders are one of the main areas of indication for the various neuromodulation techniques. This review focuses on the following techniques: DBS, repetitive transcranial magnetic stimulation (rTMS), low-intensity transcranial electrical stimulation, including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), and focused ultrasound (FUS), including high-intensity magnetic resonance-guided FUS (MRgFUS), and pulsed mode low-intensity transcranial FUS stimulation (TUS). The main clinical conditions in which neuromodulation has proven its efficacy are Parkinson's disease, dystonia, and essential tremor, mainly using DBS or MRgFUS. There is also some evidence for Tourette syndrome (DBS), Huntington's disease (DBS), cerebellar ataxia (tDCS), and axial signs (SCS) and depression (rTMS) in PD. The development of non-invasive transcranial neuromodulation techniques is limited by the short-term clinical impact of these techniques, especially rTMS, in the context of very chronic diseases. However, at-home use (tDCS) or current advances in the design of closed-loop stimulation (tACS) may open new perspectives for the application of these techniques in patients, favored by their easier use and lower rate of adverse effects compared to invasive or lesioning methods. Finally, this review summarizes the evidence for keeping the use of electromyography to optimize the identification of muscles to be treated with botulinum toxin injection, which is indicated and widely performed for the treatment of various movement disorders.

Structural network topologies are associated with deep brain stimulation outcomes in Meige syndrome

Deep brain stimulation (DBS) is an effective therapy for Meige syndrome (MS). However, the DBS efficacy varies across MS patients and the factors contributing to the variable responses remain enigmatic. We aim to explain the difference in DBS efficacy from a network perspective. We collected preoperative T1-weighted MRI images of 76 MS patients who received DBS in our center. According to the symptomatic improvement rates, all MS patients were divided into two groups: the high improvement group (HIG) and the low improvement group (LIG). We constructed group-level structural covariance networks in each group and compared the graph-based topological properties and interregional connections between groups. Subsequent functional annotation and correlation analyses were also conducted. The results indicated that HIG showed a higher clustering coefficient, longer characteristic path length, lower small-world index, and lower global efficiency compared with LIG. Different nodal betweennesses and degrees between groups were mainly identified in the precuneus, sensorimotor cortex, and subcortical nuclei, among which the gray matter volume of the left precentral gyrus and left thalamus were positively correlated with the symptomatic improvement rates. Moreover, HIG had enhanced interregional connections within the somatomotor network and between the somatomotor network and default-mode network relative to LIG. We concluded that the high and low DBS responders have notable differences in large-scale network architectures. Our study sheds light on the structural network underpinnings of varying DBS responses in MS patients.

Long-term Efficacy of Bilateral Globus Pallidus Stimulation in the Treatment of Meige Syndrome

OBJECTIVE

This study aimed to investigate the long-term efficacy and prognosis of bilateral globus pallidus internus (GPi) deep brain stimulation (DBS) in patients with benign essential blepharospasm (BEB) and complete Meige syndrome, and to search for the best therapeutic subregion within the GPi.

MATERIALS AND METHODS

Data were collected for 36 patients with Meige syndrome who underwent bilateral GPi-DBS surgery at our hospital between March 2014 and February 2022. Using the Burk-Fahn-Marsden Dystonia Rating Scale (BFMDRS)-Movement (BFMDRS-M) and BFMDRS-Disability (BFMDRS-D), the severity of the symptoms of patients with complete Meige syndrome was evaluated before surgery and at specific time points after surgery. Patients with BEB were clinically evaluated for the severity of blepharospasm using BFMDRS-M, the Blepharospasm Disability Index (BDI), and Jankovic Rating Scale (JRS). Three-dimensional reconstruction of the GPi-electrode was performed in some patients using the lead-DBS software, and the correlation between GPi subregion volume of tissue activated (VTA) and symptom improvement was analyzed in patients six months after surgery. The follow-up duration ranged from six to 99 months.

RESULTS

Compared with preoperative scores, the results of all patients at six months after surgery and final follow-up showed a significant decrease (p < 0.05) in the mean BFMDRS-M score. Among them, the average BFMDRS-M improvement rates in patients with BEB at six months after surgery and final follow-up were 60.3% and 69.7%, respectively, whereas those in patients with complete Meige syndrome were 54.5% and 58.3%, respectively. The average JRS and BDI scores of patients with BEB also decreased significantly (p < 0.05) at six months after surgery and at the final follow-up (JRS improvement: 38.6% and 49.1%, respectively; BDI improvement: 42.6% and 57.4%, respectively). We were unable to identify significantly correlated prognostic factors. There was a significant correlation between GPi occipital VTA and symptom improvement in patients at six months after surgery (r = 0.34, p = 0.025).

CONCLUSIONS

Our study suggests that bilateral GPi-DBS is an effective treatment for Meige syndrome, with no serious postoperative complications. The VTA in the GPi subregion may be related to the movement score improvement. In addition, further research is needed to predict patients with poor surgical outcomes.

Applicability of clinical genetic testing for deep brain stimulation treatment in monogenic Parkinson's disease and monogenic dystonia: a multidisciplinary team perspective

In this perspective article, we highlight the possible applicability of genetic testing in Parkinson's disease and dystonia patients treated with deep brain stimulation (DBS). DBS, a neuromodulatory technique employing electrical stimulation, has historically targeted motor symptoms in advanced PD and dystonia, yet its precise mechanisms remain elusive. Genetic insights have emerged as potential determinants of DBS efficacy. Known PD genes such as GBA, SNCA, LRRK2, and PRKN are most studied, even though further studies are required to make firm conclusions. Variable outcomes depending on genotype is present in genetic dystonia, as DYT-TOR1A, NBIA/DYTPANK2, DYT-SCGE and X-linked dystonia-parkinsonism have demonstrated promising outcomes following GPi-DBS, while varying outcomes have been documented in DYT-THAP1. We present two clinical vignettes that illustrate the applicability of genetics in clinical practice, with one PD patient with compound GBA mutations and one GNAL dystonia patient. Integrating genetic testing into clinical practice is pivotal, particularly with advancements in next-generation sequencing. However, there is a clear need for further research, especially in rarer monogenic forms. Our perspective is that applying genetics in PD and dystonia is possible today, and despite challenges, it has the potential to refine patient selection and enhance treatment outcomes.

What have we learned about the biology of dystonia from deep brain stimulation?

Deep brain stimulation has dramatically changed the management of patients with dystonia, therapeutic approach of dystonia with marked improvement of dystonia and functional disability. However, despite decades of experience and identification of good prognosis factors, prediction of beneficial effect at the individual level is still a challenge. There is inter-individual variability in therapeutic outcome. Genetic factors are identified but subgroups of patients still have relapse or worsening of dystonia in short or long term. Possible "biological factors" underlying such a difference among patients are discussed, including structural or functional differences including altered plasticity.

Pallidal Recordings in Chronically Implanted Dystonic Patients: Mitigation of Tremor-Related Artifacts

Low-frequency oscillatory patterns of pallidal local field potentials (LFPs) have been proposed as a physiomarker for dystonia and hold the promise for personalized adaptive deep brain stimulation. Head tremor, a low-frequency involuntary rhythmic movement typical of cervical dystonia, may cause movement artifacts in LFP signals, compromising the reliability of low-frequency oscillations as biomarkers for adaptive neurostimulation. We investigated chronic pallidal LFPs with the Percept^TM PC (Medtronic PLC) device in eight subjects with dystonia (five with head tremors). We applied a multiple regression approach to pallidal LFPs in patients with head tremors using kinematic information measured with an inertial measurement unit (IMU) and an electromyographic signal (EMG). With IMU regression, we found tremor contamination in all subjects, whereas EMG regression identified it in only three out of five. IMU regression was also superior to EMG regression in removing tremor-related artifacts and resulted in a significant power reduction, especially in the theta-alpha band. Pallido-muscular coherence was affected by a head tremor and disappeared after IMU regression. Our results show that the Percept PC can record low-frequency oscillations but also reveal spectral contamination due to movement artifacts. IMU regression can identify such artifact contamination and be a suitable tool for its removal.

Volume of tissue activated within subthalamic nucleus and clinical efficacy of deep brain stimulation in Meige syndrome

OBJECTIVE

The clinical efficacy of deep brain stimulation (DBS) relies on the optimal electrode placement in a large extent. Subthalamic nucleus (STN) DBS was recognized as clinically effective for Meige syndrome. This study identified the correlations of volume of tissue activated (VTA) within the motor STN and the final efficacy of the surgical procedure.

METHODS

Clinical outcomes of the patients (n=25) were evaluated with the percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale movement (BFMDRS-M) scores at the last follow-up (LFU) visit. Pearson's correlation coefficients were calculated to identify the relationship of the final clinical outcomes with the VTA within the STN, VTA within the different STN territories, and other clinical variables.

RESULTS

On the whole, the patients showed an average of 59.21% improvement at the LFU visit relative to the baseline (5.72 ± 7.31 vs. 13.70 ± 7.36, P ˂ 0.001). Active electrode contacts mainly clustered in the STN motor territories. There were significant positive correlations between the BFMDRS-M percentage improvement and VTA within the STN (Pearson r = 0.434, P = 0.039) and the STN motor territories (r = 0.430, P = 0.041), but not associative or limbic STN. Other basic clinical characteristics including age, disease duration, and preoperative scores were not significantly correlated with the final outcomes.

CONCLUSIONS

Our study further validated the efficacy of STN-DBS in even the cases with intractable Meige syndrome. Furthermore, VTA within the motor STN could serve as a potential prognostic factor for the final clinical outcomes.

Neurophysiological Basis of Deep Brain Stimulation and Botulinum Neurotoxin Injection for Treating Oromandibular Dystonia

Oromandibular dystonia (OMD) induces severe motor impairments, such as masticatory disturbances, dysphagia, and dysarthria, resulting in a serious decline in quality of life. Non-invasive brain-imaging techniques such as electroencephalography (EEG) and magnetoencephalography (MEG) are powerful approaches that can elucidate human cortical activity with high temporal resolution. Previous studies with EEG and MEG have revealed that movements in the stomatognathic system are regulated by the bilateral central cortex. Recently, in addition to the standard therapy of botulinum neurotoxin (BoNT) injection into the affected muscles, bilateral deep brain stimulation (DBS) has been applied for the treatment of OMD. However, some patients' OMD symptoms do not improve sufficiently after DBS, and they require additional BoNT therapy. In this review, we provide an overview of the unique central spatiotemporal processing mechanisms in these regions in the bilateral cortex using EEG and MEG, as they relate to the sensorimotor functions of the stomatognathic system. Increased knowledge regarding the neurophysiological underpinnings of the stomatognathic system will improve our understanding of OMD and other movement disorders, as well as aid the development of potential novel approaches such as combination treatment with BoNT injection and DBS or non-invasive cortical current stimulation therapies.

Dystonia in veterinary neurology

Dystonia is a clinical sign and main feature of many movement disorders in humans as well as veterinary species. It is characterized by sustained or intermittent involuntary muscle contractions causing abnormal (often repetitive) movements, postures, or both. This review discusses the terminology and definition of dystonia, its phenomenology, and its pathophysiology, and provides considerations regarding the diagnosis and treatment of dystonia in dogs and cats. In addition, currently recognized or reported disorders in dogs and cats in which dystonia is a particular or main feature are discussed and comparisons are made between disorders featuring dystonia in humans and animals. We suggest that when describing the phenomenology of dogs and cats with dystonia, if possible the following should be included: activity being performed at onset (e.g., resting or running or exercise-induced), body distribution, duration, responsiveness (subjective), severity, temporal pattern (i.e., paroxysmal or persistent, severity at onset and at later stages), presence or absence of autonomic signs (e.g., salivation), presence or absence of preceding signs (e.g., restlessness), presence or absence of signs after dystonia subsides (e.g., sleepiness), coexistence of other movement disorders, any other neurological manifestations, and possible links to administered medications, intoxications or other associated factors. We also suggest that dystonia be classified based on its etiology as either structural genetic, suspected genetic, reactive, or unknown.