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 x 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.