Long-term outcomes of deep brain stimulation in Parkinson disease

Abstract

The efficacy of deep brain stimulation (DBS) for Parkinson disease (PD) is well established for up to 1 or 2 years, but long-term outcome data are still limited. In this Review, we\xa0critically discuss the evidence on the long-term outcomes of DBS and consider the clinical implications. Although many patients are lost to follow-up, the evidence indicates that subthalamic nucleus DBS improves motor function for up to 10 years, although the magnitude of\xa0improvement tends to decline over time. Functional scores recorded during on-medication periods worsen more quickly than those recorded in off periods, consistent with the degeneration of non-dopaminergic pathways. Dyskinesia, motor fluctuations and activities of\xa0daily living in off periods remain improved at 5 years, but quality-of-life scores have usually fallen below preoperative levels. The incidence and severity of dementia among patients receiving DBS are comparable to those among patients who receive medical treatment. Severe\xa0adverse events are rare, but adverse events such as dysarthria are common and probably under-reported. Long-term data on the outcomes of globus pallidus interna DBS are limited and mostly confirm the efficacy for dyskinesia. A trend towards offering DBS in the earlier stages of PD creates a need to identify factors that predict long-term outcomes and to discuss realistic expectations with patients preoperatively.In this Review, Limousin and Foltynie discuss the current evidence on the long-term outcomes of deep brain stimulation in Parkinson disease and consider the clinical implications of these findings for future use of this therapeutic approach.Key pointsSubthalamic nucleus (STN) deep brain stimulation (DBS) can provide long-term improvements in motor function for patients with Parkinson disease (PD).STN DBS does not prevent the neurodegenerative processes of PD; therefore, quality-of-life scores have usually fallen to preoperative levels by the 5-year time\xa0point.Deterioration in quality of life often reflects the emergence of 3,4-dihydroxyphenylalanine (l-DOPA)-refractory or stimulation-resistant motor and non-motor features of PD, particularly impairments of gait, balance and speech.Distinguishing stimulation-induced adverse effects from disease progression requires experience, a systematic approach to adjusting stimulation parameters and awareness of possible relationships with changes in dopaminergic medication.Important factors in long-term outcomes of DBS are patient selection, precision of electrode targeting and experienced stimulation and medication adjustments.