Soha Alomar,1,2 Nicolas K. King,1 Clement Hamani,1 Andres Lozano.1
1Department of Surgery, Division of Neurosurgery, Toronto Western Hospital, University of Toronto, Toronto, Canada, 2Department of Surgery, Division of Neurosurgery, King Abdulaziz University Hospital, King Abdulaziz University, Jeddah, Saudi Arabia
Background and Objective: Thalamic surgery has been used for several decades to treat different forms of movement disorders. Ablative and non-ablative procedures are some therapeutic modalities that have been used. The former comprises the creation of thalamic lesions whereas the latter involves the nondestructive modulation of brain activity. Advancements in imaging and lesioning techniques have led to resurgence of interest in thalamotomy using different surgical techniques. The risk of developing speech difficulties after thalamotomy and deep brain stimulation of the thalamus for movement disorder varies widely in the literature. The goal of this review is to evaluate factors that are associated with higher risk, and summarize the available data. Methods: A systematic review and meta-analysis were used in this study. We searched the following databases: Medline, Medline in process, Embase, PsycInfo, CINAHL, Web of Science, Cochrane Library, Cochrane Methodology Register, Health Technology Assessment, Database of Abstracts of Review of Effects Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, we also checked cross references for some important articles by searching citing and cited articles, and retrieved studies between 1960 through September 2014. Two authors independently extracted the data. In case of disagreement a consensus was reached by review with a third author. Results: This review shows that the overall event rate of any type of speech difficulty after thalamotomy regardless of the laterality or the technique is 0.191 (CI: 0.142-0.251). Subgroup analysis by speech type showed that hypophonia was the most common speech disorder 0.277 (CI: 0.065-0.679). Unilateral procedures showed lower risk of speech impairment; with event rate of 0.1214 (CI: 0.086-0.175) and 0.397 (CI: 0.282-0.524) in the bilateral group. A subgroup analysis for the hemispheric side of the lesion was carried out. Left sided procedures showed higher risk of speech impairment post thalamotomy. Right-sided procedures showed an event rate of 0.146 (CI: 0.089-0.23) and left sided 0.469 (CI: 0.296-0.651). An analysis of the subgroup was carried out by disease; the highest risk for speech impairment was in the mixed group. The event rate was 0.177 (CI: 0.096-0.30) followed by PD, then dystonia, then ET. A subgroup analysis by thalamotomy technique in the unilateral group was made. Mixed technique series showed 0.289 event rate of speech difficulty (CI: 0.089-0.628), followed by radiofrequency lesioning 0.122 (CI: 0.074-0.194) and Gamma knife was the lowest with 0.046 (CI: 0.023-0.088). After bilateral DBS, the risk of speech difficulty is 0.36 (CI: 0.23-0.51) while after unilateral the risk is 0.14 (CL: 0.10 -0.20). The most commonly reported speech disorder after thalamic DBS is stimulation related dysarthria. In unilateral procedures, the reported dysarthria risk is 0.16 (CI: 0.10-0.25) followed by dysphasia 0.098 (CI: 0.042-0.216) then by hypophonia 0.071 (CI: 0.018-0.244). Limitations: This study is limited by the retrospective nature of the studies included and the heterogeneity among these studies. Conclusion: There are several factors that carry higher risk of developing speech difficulty after thalamotomy, including bilateral, left sided procedures, and some older lesioning techniques. The most commonly reported speech complication after thalamic DBS for movement disorder is stimulation related dysarthria, which is higher after bilateral procedures and mostly reversible.