Stimulation-induced side effects in the posterior subthalamic area: distribution, characteristics and visualization.

OBJECTIVE: The posterior subthalamic area (PSA) is an emerging but relatively unexplored target for DBS treatment of tremor. The aim of the study was to explore the area further by evaluating the spatial distribution and the characteristics of stimulation-induced side effects in this area. METHODS: Twenty-eight patients with essential tremor (ET) implanted with 33 DBS electrodes were evaluated concerning stimulation-induced side effects by testing each contact separately one year after surgery. The location of the side effects were plotted on axial slides of the Morel Stereotactic Atlas and a 3-dimensional model of the area for visualization was created. RESULTS: Visualization of the contacts eliciting stimulation-induced side effects demonstrated that identical responses can be elicited from various points in the PSA and its vicinity. The majority of contacts inducing muscular affection and cerebellar symptoms, including dysarthria, could not be attributed to an effect on the internal capsule. Paresthesias, affecting various body parts were elicited throughout the area without a clear somatotopic pattern. CONCLUSION: Stimulation-induced side effects in the PSA and its vicinity were difficult to attribute to certain anatomical areas as the same response was induced from various locations. Therefore, this study could not provide a meaningful somatotopic map with regard to stimulation-induced side effects in the PSA.

Complications and side effects of deep brain stimulation in the posterior subthalamic area.

BACKGROUND: The posterior subthalamic area (PSA), including the zona incerta and prelemniscal radiation (Raprl), has recently been presented in number of publications as a promising target for deep brain stimulation (DBS) in the treatment of various movement disorders. In order to evaluate the safety of the procedure, we analyzed our initial 40 patients for complications and side effects. METHODS: 40 patients treated with PSA DBS for Parkinson's disease, essential tremor and other forms of tremor were included. RESULTS: The most severe complication was 1 transient mild hemiparesis and 1 infection. Minor complications and side effects were relatively frequent, including mild transient dysphasia in 22.5% of the patients. CONCLUSIONS: Few serious complications were encountered, and we consider the PSA to be a safe target for DBS.

Deep brain stimulation of the posterior subthalamic area in the treatment of tremor.

BACKGROUND: Several studies have described lesional therapy in the posterior subthalamic area (PSA) in the treatment of various movement disorders. Recently, some publications have illustrated the effect of deep brain stimulation (DBS) in this area in patients with Parkinson's disease, essential tremor, MS-tremor, and other forms of tremor. Even though the clinical series is small, the reported benefits prompted us to explore DBS in this area in the treatment of tremor. METHOD: Five patients with tremor were operated using unilateral DBS of the PSA. Two patients had dystonic tremor, one primary writing tremor, one cerebellar tremor and the other neuropathic tremor. All patients were assessed before and 1 year after surgery using items 5 and 6 (tremor of the upper extremity), 11-14 (hand function), and when appropriate item 10 (handwriting) from the essential tremor rating scale. FINDINGS: The mean improvement on stimulation after 1 year was 87%. A pronounced and sustained microlesional effect was seen in several of the patients, and while the mean improvement off stimulation was 56% the reduction in the three patients with the most pronounced effect was 89%. The two patients with dystonic tremor did also become free of the dystonic symptoms and pain in the treated arm. No severe complication occurred. CONCLUSIONS: DBS of the PSA in this small group of patients had an excellent effect on the different forms of tremor, except for the neuropathic tremor where the effect was moderate. These preliminary results suggest PSA to be an effective target for the treatment of various forms of tremor. Further studies concerning indications, safety and efficacy of DBS in the posterior subthalamic area are required.