Probabilistic maps for deep brain stimulation - Impact of methodological differences.

BACKGROUND: Group analysis of patients with deep brain stimulation (DBS) has the potential to help understand and optimize the treatment of patients with movement disorders. Probabilistic stimulation maps (PSM) are commonly used to analyze the correlation between tissue stimulation and symptomatic effect but are applied with different methodological variations. OBJECTIVE: To compute a group-specific MRI template and PSMs for investigating the impact of PSM model parameters. METHODS: Improvement and occurrence of dizziness in 68 essential tremor patients implanted in caudal zona incerta were analyzed. The input data includes the best parameters for each electrode contact (screening), and the clinically used settings. Patient-specific electric field simulations (n = 488) were computed for all DBS settings. The electric fields were transformed to a group-specific MRI template for analysis and visualization. The different comparisons were based on PSMs representing occurrence (N-map), mean improvement (M-map), weighted mean improvement (wM-map), and voxel-wise t-statistics (p-map). These maps were used to investigate the impact from input data (clinical/screening settings), clustering methods, sampling resolution, and weighting function. RESULTS: Screening or clinical settings showed the largest impacts on the PSMs. The average differences of wM-maps were 12.4 and 18.2% points for the left and right sides respectively. Extracting clusters based on wM-map or p-map showed notable variation in volumes, while positioning was similar. The impact on the PSMs was small from weighting functions, except for a clear shift in the positioning of the wM-map clusters. CONCLUSION: The distribution of the input data and the clustering method are most important to consider when creating PSMs for studying the relationship between anatomy and DBS outcome.

Ipsilateral Effects of Unilateral Deep Brain Stimulation for Essential Tremor.

BACKGROUND: Essential tremor (ET) is the most common adult movement disorder. For the relatively large group of patients who do not respond adequately to pharmacological therapy, deep brain stimulation (DBS) is a well-established treatment option. Most ET patients will have bilateral symptoms, and many of them receive bilateral DBS. Unilateral DBS is however still the most common procedure, and some papers suggest an ipsilateral effect in these patients. OBJECTIVES: The aim of this study was to analyze if there is an ipsilateral effect of DBS for ET. METHOD: We retrospectively analyzed our patient cohort with DBS surgery from 1996 to 2017, selecting patients with ET that underwent surgery with unilateral DBS without previous DBS or lesional surgery. A total number of 68 patients (39 males, 29 females) were identified. The patients were evaluated twice: first, at a mean time of 12 months after surgery defined as short-term follow-up and then again at a mean time of 49 months after surgery defined as long-term follow-up, using the clinical rating scale for tremor (CRST). RESULTS: The total CRST score was reduced from mean 49.5 points at baseline before surgery to 20.2 (p < 0.001) at short-term and 28.3 (p < 0.001) at long-term follow-up. Contralateral tremor was reduced from mean 6.1 to 0.4 (p < 0.001) and 1.2 (p < 0.001), respectively. Contralateral hand function was reduced from 11.5 to 2.6 (p < 0.001) and 4.6 (p < 0.001), respectively. Ipsilateral hand function scored 9 at baseline, 8.3 at 1 year, and then again 9.4 at long-term follow-up. Ipsilateral tremor scored 4.0 at baseline, 3.7 at 1 year, and 4.3 at long-term follow-up. Neither ipsilateral hand function nor ipsilateral tremor showed significant difference. CONCLUSIONS: There was no difference in severity of ipsilateral tremor, neither at 1 year nor in the long term. We believe ipsilateral effects of DBS for ET merits limited consideration regarding decision-making or patient counseling before surgery.

Risk factors for postoperative myocardial infarct following cholecystectomy: a population-based study.

BACKGROUND: The aim was to analyse the risk for myocardial infarction (MI) after cholecystectomy. METHODS: The study is based on data from the Swedish Register for Gallstone Surgery (GallRiks) 2006-2014. The cohort was cross-linked with the Swedish Patient Register. Standardised incidence ratio (SIR) was calculated by dividing the observed incidence of MI within 30 days after surgery with the expected incidence of the background population. RESULTS: Altogether 94,577 procedures were included. MI within 30 days postoperatively (30d-po) were registered in 87 cases (0.09%, SIR for MI 3.03; 95% CI 2.43-3.74). MI occurred more often in men (0.15% vs 0.06%), after open surgery (0.34% vs 0.04%), was age related (age >50 years OR 4.05 > 75 years OR 15.70) and occurred more frequently amongst those with gallstone complications and high ASA score (ASA 1; 0.02%, 2; 0.08%, ≥3; 0,64%). The risk for MI within 30d-po was 52.8% if the patient had suffered an infarct within 8 weeks preoperatively. Laparoscopy converted to open and primarily open surgery were independent risk factors (OR 3.05 vs 2.19). The mortality in the group with 30d-po MI was 11.5% vs 0.02%. CONCLUSION: Delaying elective cholecystectomy for at least 8 weeks after a recent MI reduces the risk for postoperative MI.