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Functional improvement after subthalamic stimulation in Parkinson’s disease: a non-equivalent controlled study with 12–24 month follow up

Objective: This study aimed to assess the effectiveness of chronic bilateral STN-S in improving the functional status of PD patients compared with patients treated with drugs alone. Methods: Controlled study of disability index changes over 12 and 24 month chronic STN stimulation. Of 39 patients with advanced PD meeting CAPSIT criteria for STN-S, 23 underwent surgery; 16 patients decided against surgery and continued on drug schedule adjustments. Functional status was measured using the Activities of Daily Living section of the Unified Parkinson’s Disease Rating Scale (UPDRS-ADL), Brown’s Disability Scale, and Functional Independence Measure. UPDRS motor score and subscores for selected items, levodopa equivalent daily dose, and Beck Depression Inventory scores were also monitored. Results: T12 follow up data were available for all 39 patients and T24 data for 13 STN-S and 8 control subjects. Compared with controls, STN-S patients experienced significant or highly significant improvements in all independence measures at both 12 and 24 months (time × treatment effect T12: F = 19.5, p = 0.00008; T24: F = 6.2, p = 0.005). Forward stepwise regression for independent predictors of the yearly rate of UPDRS-ADL score modification in the entire sample showed that treatment was the only factor significantly associated with functional status change (beta coefficient −0.54, t value −2.5, p = 0.02), whereas other variables—UPDRS motor score, BDI, and age at disease onset and enrolment—were not in the equation. Conclusion: STN-S is an effective therapeutic option in advanced PD. It induced a consistent improvement of functional abilities over two years to an extent that was not achieved with drug therapy alone.