Role of Functional neurosurgery in Improving Patient Outcomes in Epilepsy, Movement Disorders, and Chronic Pain.

Functional neurosurgery encompasses surgical procedures geared towards treating movement disorders (such as Parkinson's disease and essential tremor), drug-resistant epilepsy, and various types of pain disorders. It is one of the most rapidly expanding fields within neurosurgery and utilizes both traditional open surgical methods such as open temporal lobectomy for epilepsy as well as neuromodulation-based treatments such as implanting brain or nerve stimulation devices. This review outlines the role functional neurosurgery plays in treatment of epilepsy, movement disorders, and pain, and how it is being implemented at the University of Missouri by the Department of Neurosurgery.

Intracranial Bleeding in Deep Brain Stimulation Surgery: A Systematic Review and Meta-Analysis.

BACKGROUND: Deep brain stimulation (DBS) is a neurosurgical treatment used for the treatment of movement disorders. Surgical and perioperative complications, although infrequent, can result in clinically significant neurological impairment. OBJECTIVES: In this study, we evaluated the incidence and risk factors of intracranial bleeding in DBS surgery. METHOD: Medline, EMBASE, and Cochrane were screened in line with PRISMA 2020 guidelines to capture studies reporting on the incidence of hemorrhagic events in DBS. After removing duplicates, the search yielded 1,510 papers. Abstracts were evaluated by two independent reviewers for relevance. A total of 386 abstracts progressed to the full-text screen and were assessed against eligibility criteria. A total of 151 studies met the criteria and were included in the analysis. Any disagreement between the reviewers was resolved by consensus. Relevant data points were extracted and analyzed in OpenMeta [Analyst] software. RESULTS: The incidence of intracranial bleeding was 2.5% (95% CI: 2.2-2.8%) per each patient and 1.4% (95% CI: 1.2-1.6%) per each implanted lead. There was no statistically significant difference across implantation targets and clinical indications. Patients who developed an intracranial bleed were on average 5 years older (95% CI: 1.26-13.19), but no difference was observed between the genders (p = 0.891). A nonsignificant trend was observed for a higher risk of bleeding in patients with hypertension (OR: 2.99, 95% CI: 0.97-9.19) (p = 0.056). The use of microelectrode recording did not affect the rate of bleeding (p = 0.79). CONCLUSIONS: In this review, we find that the rate of bleeding per each implanted lead was 1.4% and that older patients had a higher risk of hemorrhage.

Neurosurgical management of non-spastic movement disorders.

BACKGROUND: Non-spastic movement disorders in children are common, although true epidemiologic data is difficult to ascertain. Children are more likely than adults to have hyperkinetic movement disorders defined as tics, dystonia, chorea/athetosis, or tremor. These conditions manifest from acquired or heredodegenerative etiologies and often severely limit function despite medical and surgical management paradigms. Neurosurgical management for these conditions is highlighted. METHODS: We performed a focused review of the literature by searching PubMed on 16 May 2023 using key terms related to our review. No temporal filter was applied, but only English articles were considered. We searched for the terms (("Pallidotomy"[Mesh]) OR "Rhizotomy"[Mesh]) OR "Deep Brain Stimulation"[Mesh], dystonia, children, adolescent, pediatric, globus pallidus, in combination. All articles were reviewed for inclusion in the final reference list. RESULTS: Our search terms returned 37 articles from 2004 to 2023. Articles covering deep brain stimulation were the most common (n = 34) followed by pallidotomy (n = 3); there were no articles on rhizotomy. DISCUSSION: Non-spastic movement disorders are common in children and difficult to treat. Most of these patients are referred to neurosurgery for the management of dystonia, with modern neurosurgical management including pallidotomy, rhizotomy, and deep brain stimulation. Historically, pallidotomy has been effective and may still be preferred in subpopulations presenting either in status dystonicus or with high risk for hardware complications. Superiority of DBS over pallidotomy for secondary dystonia has not been determined. Rhizotomy is an underutilized surgical tool and more study characterizing efficacy and risk profile is indicated.

Navigated Deep Brain Stimulation Surgery: Evaluating the Combined Use of a Frame-Based Stereotactic System and a Navigation System.

Deep brain stimulation (DBS) is a complex surgical procedure that requires detailed anatomical knowledge. In many fields of neurosurgery navigation systems are used to display anatomical structures during an operation to aid performing these surgeries. In frame-based DBS, the advantage of visualization has not yet been evaluated during the procedure itself. In this study, we added live visualization to a frame-based DBS system, using a standard navigation system and investigated its accuracy and potential use in DBS surgery. As a first step, a phantom study was conducted to investigate the accuracy of the navigation system in conjunction with a frame-based approach. As a second step, 5 DBS surgeries were performed with this combined approach. Afterwards, 3 neurosurgeons and 2 neurologists with different levels of experience evaluated the potential use of the system with a questionnaire. Moreover, the additional personnel, costs and required set up time were noted and compared to 5 consecutive standard procedures. In the phantom study, the navigation system showed an inaccuracy of 2.1 mm (mean SD 0.69 mm). In the questionnaire, a mean of 9.4/10 points was awarded for the use of the combined approach as a teaching tool, a mean of 8.4/10 for its advantage in creating a 3-dimensional (3-D) map and a mean of 8/10 points for facilitating group discussions. Especially neurosurgeons and neurologists in training found it useful to better interpret clinical results and side effects (mean 9/10 points) and neurosurgeons appreciated its use to better interpret microelectrode recordings (mean 9/10 points). A mean of 6/10 points was awarded when asked if the benefits were worth the additional efforts. Initially 2 persons, then one additional person was required to set up the system with no relevant added time or costs. Using a navigation system for live visualization during frame-based DBS surgery can improve the understanding of the complex 3-D anatomy and many aspects of the procedure itself. For now, we would regard it as an excellent teaching tool rather than a necessity to perform DBS surgeries.

Surgical Outcomes for Severe Idiopathic Toe Walkers.

BACKGROUND: Idiopathic toe walking (ITW) is a diagnosis of exclusion and represents a spectrum of severity. Treatment for ITW includes observation and a variety of conservative treatment methods, with surgical intervention often reserved for severe cases. Previous studies reviewing treatment outcomes are often difficult to interpret secondary to a mixture of case severity. The goal of this study was to review surgical outcomes in patients with severe ITW who had failed prior conservative treatment, as well as determine differences in outcomes based on the type of surgery performed. METHODS: After IRB approval, all patients with surgical management of severe ITW at a single institution were identified. Zone II or zone III plantar flexor lengthenings were performed in all subjects. Clinical, radiographic, and motion analysis data were collected preoperatively and at 1 year following surgery. RESULTS: Twenty-six patients (46 extremities) with a diagnosis of severe ITW from 2002 to 2017 were included. Zone II lengthenings were performed in 25 extremities (mean age=9.9 y) and zone III lengthenings were performed in 21 extremities (mean age=8.6 y). At the most recent follow-up, 100% of zone III lengthening extremities and 88% of zone II lengthening demonstrated decreased severity of ITW. Six extremities required additional treatment, all of which were initially managed with zone II lengthenings. CONCLUSIONS: Severe ITW or ITW that has not responded to conservative treatment may benefit from surgical intervention. More successful outcomes, including continued resolution of toe walking, were observed in subjects treated with zone III lengthenings. LEVEL OF EVIDENCE: Level III-case series.

Psychosurgery in the History of Stereotactic Functional Neurosurgery.

The paper invites to reappraise the role of psychosurgery for and within the development of functional stereotactic neurosurgery. It highlights the significant and long-lived role of stereotactic neurosurgery in the treatment of severe and chronic mental disorders. Stereotactic neurosurgery developed out of psychosurgery. It was leucotomy for psychiatric disorders and chronic pain that paved the way for stereotactic dorsomedial thalamotomy in these indications and subsequently for stereotactic surgery in epilepsy and movement disorders. Through the 1960s stereotactic psychosurgery continued to progress in silence. Due to the increased applications of stereotactic surgery in psychiatric indications, psychosurgery's renaissance was proclaimed in the early 1970s. At the same time, however, a public fearing mind control started to discredit all functional neurosurgery for mental disorders, including stereotactic procedures. In writing its own history, stereotactic neurosurgery's identity as a neuropsychiatric discipline became subsequently increasingly redefined as principally a sort of "surgical neurology," cut off from its psychiatric origin.

Emergency presentations of movement disorders.

Movement disorders are typically perceived as being gradually progressive conditions that are managed in outpatient settings. However, they may manifest de novo with an acute severe phenotype or an acute decompensation. A movement disorder becomes an emergency when it evolves acutely or subacutely over hours to days; delays in its diagnosis and treatment may cause significant morbidity and mortality. Here we address the clinical presentation, diagnosis and management of those movement disorder emergencies that are principally encountered in emergency departments, in acute receiving units or in intensive care units. We provide practical guidance for management in the acute setting where there are several treatable causes not to be missed. The suggested medication doses are predominantly based on expert opinion due to limited higher-level evidence. In spite of the rarity of movement disorder emergencies, neurologists need to be familiar with the phenomenology, potential causes and treatments of these conditions. Movement disorder emergencies divide broadly into two groups: hypokinetic and hyperkinetic, categorised according to their phenomenology. Most acute presentations are hyperkinetic and some are mixed.

Deep Brain Stimulation in Movement Disorders: From Experimental Surgery to Evidence-Based Therapy.

Deep brain stimulation (DBS) of 3 different targets is the most important therapeutic innovation of the past 30 years for patients with fluctuating Parkinson's disease (PD), disabling dystonia, tremors, and refractory Gilles de la Tourette syndrome. When compared with medical treatment alone, controlled studies have shown better motor, nonmotor, and particularly quality-of-life outcomes with large effect sizes for advanced complicated PD that cannot be improved with medication, and also for PD patients with only early fluctuations. Class 1 studies have also shown superiority over medical treatment for generalized, segmental, and botulinum-toxin refractory focal cervical dystonia. Long-term efficacy is established for all indications with open studies. For tremors, open studies have shown that DBS is remarkably effective on PD and essential tremor, but efficacy on severe essential tremor and cerebellar tremors is limited by a tendency for tolerance/habituation, including concerns about long-term efficacy. Open studies of disabling Gilles de la Tourette syndrome show an improvement in tics. New developments hold a promise for further improvement. New hardware with directional stimulation and new stimulation paradigms are further areas of research. The targets of DBS are refined with new imaging processing that will help to diversify the surgical targets. New indications are being explored. Closed-loop DBS using brain or peripheral sensor signals have shown favorable clinical short-term results. Long-term data are lacking, and it is hoped that similar approaches for other movement or behavioral disorders may be developed. Exciting new developments carry the hope for a more pathophysiology-based approach for DBS for various brain circuit disorders. © 2019 International Parkinson and Movement Disorder Society.

Ablative brain surgery: an overview.

Background: Ablative therapies have been used for the treatment of neurological disorders for many years. They have been used both for creating therapeutic lesions within dysfunctional brain circuits and to destroy intracranial tumors and space-occupying masses. Despite the introduction of new effective drugs and neuromodulative techniques, which became more popular and subsequently caused brain ablation techniques to fall out favor, recent technological advances have led to the resurgence of lesioning with an improved safety profile. Currently, the four main ablative techniques that are used for ablative brain surgery are radiofrequency thermoablation, stereotactic radiosurgery, laser interstitial thermal therapy and magnetic resonance-guided focused ultrasound thermal ablation. Object: To review the physical principles underlying brain ablative therapies and to describe their use for neurological disorders. Methods: The literature regarding the neurosurgical applications of brain ablative therapies has been reviewed. Results: Ablative treatments have been used for several neurological disorders, including movement disorders, psychiatric disorders, chronic pain, drug-resistant epilepsy and brain tumors. Conclusions: There are several ongoing efforts to use novel ablative therapies directed towards the brain. The recent development of techniques that allow for precise targeting, accurate delivery of thermal doses and real-time visualization of induced tissue damage during the procedure have resulted in novel techniques for cerebral ablation such as magnetic resonance-guided focused ultrasound or laser interstitial thermal therapy. However, older techniques such as radiofrequency thermal ablation or stereotactic radiosurgery still have a pivotal role in the management of a variety of neurological disorders.

Accuracy in Deep Brain Stimulation Electrode Placement: A Single-Surgeon Retrospective Analysis of Sterotactic Error in Overlapping and Non-Overlapping Surgical Cases.

BACKGROUND: Many surgeons utilize assistants to perform procedures in more than one operating room at a given time using a practice known as overlapping surgery. Debate has continued as to whether overlapping surgery improves the efficiency and access to care or risks patient safety and outcomes. OBJECTIVE: To examine effects of overlapping surgery in deep brain stimulation (DBS) for movement disorders. METHODS: In this retrospective analysis of overlapping and non-overlapping cases, we evaluated stereotactic accuracy, operative duration, length of hospital stay, and the presence of hemorrhage, wound-related complications, and hardware-related complications requiring revision in adults with movement disorders undergoing DBS. RESULTS: Of 324 cases, 141 (43.5%) were overlapping and 183 (56.5%) non-overlapping. Stereotactic error, number of brain penetrations, and postoperative length of hospitalization did not differ significantly (p ≥ 0.08) between the overlapping and non-overlapping groups. Mean operative duration was significantly longer for overlapping (81/141 [57.4%], 189.5 ± 10.8 min) than for non-overlapping cases (79/183 [43.2%], 169.9 ± 7.6 min; p = 0.004). There were no differences in rates of wound-related complications or hemorrhages, but overlapping cases had a significantly higher rate of hardware-related complications requiring revision (7/141 [5.0%] vs. 0/183 [0%]; p = 0.002). CONCLUSIONS: Overlapping and non-overlapping cases had comparable DBS lead placement accuracy. Overlapping cases had a longer operative duration and had a higher rate of hardware-related complications requiring revision.

The Origins of Human Functional Stereotaxis: A Reappraisal.

In order to shed light on the first application of human functional stereotactic neurosurgery, whether it was in the realm of movement disorders, as has been claimed repeatedly, or in the realm of psychiatry, a review of the original scholarly literature was conducted. Tracking and scrutinising original publications by Spiegel and Wycis, the pioneers of human stereotactic neurosurgery, it was found that its origin and the very incentive for its development and first clinical use were to avoid the side effects of frontal leucotomy. The first applications of functional stereotactic neurosurgery were in performing dorsomedial thalamotomies in psychiatric patients; it was only later that the stereotactic technique was applied in patients with chronic pain, movement disorders and epilepsy. Spiegel and Wycis' first functional stereotactic operations were for obsessive-compulsive disorder, schizophrenia, and other psychiatric conditions.

Endoscopic spinal surgery using a new tubular retractor with 15 mm outer diameter.

Purpose: To assess whether the instrument handling and image quality of endoscopic spinal decompression procedures is adequate and effects the treatment of degenerative spinal disorders. Material and Methods: Forty-six patients underwent endoscopic procedures for radicular pain or sensorimotor deficit due to a degenerative disorder using a 15mm tubular retractor. Endoscopic video recordings were reviewed with focus on instrument handling and intraoperative complication. At final follow-up the clinical outcome was assessed via a standardized questionnaire including the Oswestry Disability Index (ODI) Neck Disability Index (NDI), Odoms criteria and a personal examination focusing on pain, and sensorimotor deficits. Results: Forty out of 46 patients attended a final follow-up (86.9%). The mean follow-up time was 51.8 month (range 15-84 month). At final follow-up, of patients who were operate at the lumbar spine 93.9% and at the cervical spine 85.7% were free of radicular pain, no weakness was documented in 84.9% of cases after lumbar and 85.7% after cervical spine procedure, and according to Odoms criteria clinical success was noted in 84.5% and 100%, respectively. The mean ODI was 9.0% and mean NDI was 11.7%. The dural tear rate was 4.3%, all dural tear were closed endoscopically. The recurrent disc herniation rate was 6.1%. Conclusions: Endoscopic decompression using a 15m tubular retractor offers a good view onto the surgical field and a high clinical success rate. The decompression of degenerative pathologies in bimanual technique is not limited by a 15mm tubular retractor.

A Delay between Motor Cortex Lesions and Neuronal Transplantation Enhances Graft Integration and Improves Repair and Recovery.

We previously reported that embryonic motor cortical neurons transplanted immediately after lesions in the adult mouse motor cortex restored damaged motor cortical pathways. A critical barrier hindering the application of transplantation strategies for a wide range of traumatic injuries is the determination of a suitable time window for therapeutic intervention. Here, we report that a 1 week delay between the lesion and transplantation significantly enhances graft vascularization, survival, and proliferation of grafted cells. More importantly, the delay dramatically increases the density of projections developed by grafted neurons and improves functional repair and recovery as assessed by intravital dynamic imaging and behavioral tests. These findings open new avenues in cell transplantation strategies as they indicate successful brain repair may occur following delayed transplantation.SIGNIFICANCE STATEMENT Cell transplantation represents a promising therapy for cortical trauma. We previously reported that embryonic motor cortical neurons transplanted immediately after lesions in the adult mouse motor cortex restored damaged cortical pathways. A critical barrier hindering the application of transplantation strategies for a wide range of traumatic injuries is the determination of a suitable time window for therapeutic intervention. We demonstrate that a 1 week delay between the lesion and transplantation significantly enhances graft vascularization, survival, proliferation, and the density of the projections developed by grafted neurons. More importantly, the delay has a beneficial impact on functional repair and recovery. These results impact the effectiveness of transplantation strategies in a wide range of traumatic injuries for which therapeutic intervention is not immediately feasible.

The Pioneering and Unknown Stereotactic Approach of Roeder and Orthner from Göttingen. Part II: Long-Term Outcome and Postmortem Analysis of Bilateral Pallidotomy in the Pre-Levodopa Era.

Before the advent of levodopa, pallidotomy was initially the most effective treatment for Parkinson disease, but it was soon superseded by thalamotomy. It is widely unknown that, similar to Leksell, 2 neurologists from Göttingen, Orthner and Roeder, perpetuated pallidotomy against the mainstream of their time. Postmortem studies demonstrated that true posterior and ventral pallidoansotomy sparing the overwhelming mass of the pallidum was accomplished. This was due to a unique and individually tailored stereotactic technique even allowing bilateral staged pallidotomies. In 1962, the long-term effects (3-year follow-up on average) of the first 18 out of 36 patients with staged bilateral pallidotomies were reported in great detail. Meticulous descriptions of each case indicate long-term improvements in parkinsonian rigidity and associated pain, as well as posture, gait, and akinesia (e.g., improved repetitive movements and arm swinging). Alleviation of tremor was found to require larger lesions than needed for suppression of rigidity. No improvement in speech, drooling, or seborrhea was observed. By 1962, the team had operated 13 patients with postencephalitic oculogyric crises with remarkable results (mean follow-up: 5 years). They also described alleviation of nonparkinsonian hyperkinetic disorders (e.g., hemiballism and chorea) with pallidotomy. The reported rates for surgical mortality and other complications had been remarkably low, even if compared to those reported after the revival of pallidotomy by Laitinen in the post-levodopa era. This applies also to bilateral pallidotomy performed with a positive risk-benefit ratio that has remained unparalleled to date. The intricate history of pallidotomy for movement disorders is incomplete without an appreciation of the achievements of the Göttingen group.

Newer advances in lesional surgery for movement disorders.

An analysis of the existing literature on lesioning for movement disorders was undertaken to review lesion therapy and its advances. Advances in imaging technology and electrophysiological techniques used for localization of brain structures and its functions, such as microelectrode recordings and macrostimulation, have greatly improved the ability to accurately identify the target nuclei such as the ventrointermediate nucleus (Vim), globus pallidus interna (GPi) and subthalamic nucleus (STN). Many important changes are happening in the understanding of lesion making. Its application as a cheaper modality of treatment; being less cumbersome; having a wider geographical appeal; and more options to create a lesion, appeals to the clinician. The procedure is undergoing a revival.

Seventy Years with the Globus Pallidus: Pallidal Surgery for Movement Disorders Between 1947 and 2017.

The year 2017 marks the 70th anniversary of the birth of human stereotactic neurosurgery. The first procedure was a pallidotomy for Huntington's disease. However, it was for Parkinson's disease that pallidotomy was soon adopted worldwide. Pallidotomy was abandoned in the late 1950s in favor of thalamotomy because of the latter's more striking effect on tremor. The advent of levodopa put a halt to all surgery for PD. In the mid-1980s, Laitinen reintroduced the posteroventral pallidotomy of Leksell, and this procedure spread worldwide thanks to its efficacy on most parkinsonian symptoms including levodopa-induced dyskinesias and thanks to basic scientific work confirming the role of the globus pallidus internus in the pathophysiology of PD. With the advent of deep brain stimulation of the subthalamic nucleus, pallidotomy was again abandoned, and even DBS of the GPi has been overshadowed by STN DBS. The GPi reemerged in the late 1990s as a major stereotactic target for DBS in dystonia and, recently, in Tourette syndrome. Lately, lesioning of the GPI is being proposed to treat refractory status dystonicus or to treat DBS withdrawal syndrome in PD patients. Hence, the pallidum as a stereotactic target for either lesioning or DBS has been the phoenix of functional stereotactic neurosurgery, constantly abandoned and then rising again from its ashes. This review is a tribute to the pallidum on its 70th anniversary as a surgical target for movement disorders, analyzing its ebbs and flows and highlighting its merits, its versatility, and its resilience. © 2017 International Parkinson and Movement Disorder Society.

Advances in surgery for movement disorders.

Movement disorder surgery has evolved throughout history as our knowledge of motor circuits and ways in which to manipulate them have expanded. Today, the positive impact on patient quality of life for a growing number of movement disorders such as Parkinson's disease is now well accepted and confirmed through several decades of randomized, controlled trials. Nevertheless, residual motor symptoms after movement disorder surgery such as deep brain stimulation and lack of a definitive cure for these conditions demand that advances continue to push the boundaries of the field and maximize its therapeutic potential. Similarly, advances in related fields - wireless technology, artificial intelligence, stem cell and gene therapy, neuroimaging, nanoscience, and minimally invasive surgery - mean that movement disorder surgery stands at a crossroads to benefit from unique combinations of all these developments. In this minireview, we outline some of these developments as well as evidence supporting topics of recent discussion and controversy in our field. Moving forward, expectations remain high that these improvements will come to encompass an even broader range of patients who might benefit from this therapy and decrease the burden of disease associated with these conditions. © 2016 International Parkinson and Movement Disorder Society.

Current applications and limitations of surgical treatments for movement disorders.

Functional neurosurgery for the treatment of both psychiatric and neurological disorders has been performed regularly since the 1940s. However, misuse in the early days and the appearance of effective medical treatments, such as levodopa and neuroleptic drugs, greatly reduced surgical approaches over several decades. The development of a comprehensive model of basal ganglia pathophysiology in the 1990s facilitated the resurgence of functional neurosurgery, mainly for the treatment of levodopa-related motor complications in Parkinson's disease. This led first to the re-emergence of posteroventral pallidotomy and subsequently to deep brain stimulation. Thirty years on from this turning point, we find ourselves looking at a new scenario. Although deep brain stimulation is accepted worldwide and technical advances continue to improve this therapy, new questions and challenges such as long-term benefits and optimal targeting have emerged. In addition, new nonincisional tools used to perform ablative treatments, such as high-intensity focused ultrasound and gamma-knife, are challenging classical reluctance to therapeutic lesioning, and it remains to be determined how these approaches will fit into the array of movement disorder treatments. This review discusses the current clinical state of the art of functional neurosurgery in the treatment of Parkinson's disease, tremor, and dystonia. © 2017 International Parkinson and Movement Disorder Society.

Speech and language adverse effects after thalamotomy and deep brain stimulation in patients with movement disorders: A meta-analysis.

BACKGROUND: The thalamus has been a surgical target for the treatment of various movement disorders. Commonly used therapeutic modalities include ablative and nonablative procedures. A major clinical side effect of thalamic surgery is the appearance of speech problems. OBJECTIVE: This review summarizes the data on the development of speech problems after thalamic surgery. METHODS: A systematic review and meta-analysis was performed using nine databases, including Medline, Web of Science, and Cochrane Library. We also checked for articles by searching citing and cited articles. We retrieved studies between 1960 and September 2014. RESULTS: Of a total of 2,320 patients, 19.8% (confidence interval: 14.8-25.9) had speech difficulty after thalamotomy. Speech difficulty occurred in 15% (confidence interval: 9.8-22.2) of those treated with a unilaterally and 40.6% (confidence interval: 29.5-52.8) of those treated bilaterally. Speech impairment was noticed 2- to 3-fold more commonly after left-sided procedures (40.7% vs. 15.2%). Of the 572 patients that underwent DBS, 19.4% (confidence interval: 13.1-27.8) experienced speech difficulty. Subgroup analysis revealed that this complication occurs in 10.2% (confidence interval: 7.4-13.9) of patients treated unilaterally and 34.6% (confidence interval: 21.6-50.4) treated bilaterally. After thalamotomy, the risk was higher in Parkinson's patients compared to patients with essential tremor: 19.8% versus 4.5% in the unilateral group and 42.5% versus 13.9% in the bilateral group. After DBS, this rate was higher in essential tremor patients. CONCLUSION: Both lesioning and stimulation thalamic surgery produce adverse effects on speech. Left-sided and bilateral procedures are approximately 3-fold more likely to cause speech difficulty. This effect was higher after thalamotomy compared to DBS. In the thalamotomy group, the risk was higher in Parkinson's patients, whereas in the DBS group it was higher in patients with essential tremor. Understanding the pathophysiology of speech disturbance after thalamic procedures is a priority. © 2017 International Parkinson and Movement Disorder Society.