Biomarkers used and Physiological changes seen with Deep Brain Stimulation in Parkinson's: A review of the literature for clinically useful biomarkers and potential biomarkers of the Future.

BACKGROUND: Parkinson's disease (PD) remains a common neurodegenerative disorder. Functional neurosurgery largely arose with the introduction of deep brain stimulation (DBS) as a potential option for PD unresponsive to medical management. Biomarkers are clinical and laboratory indicators of therapeutic success or failure.

OBJECTIVES: To examine the current and published literature relating to the development and use of biomarkers in monitoring and determining the efficacy of DBS in PD.

METHODS: Pubmed database was systematically searched using the PRISMA guidelines for systemic reviews. Studies, which examined current or potential biomarkers measurable after DBS, were included. Articles from 1952 through the present were examined.

RESULTS: The initial search identified 49 articles. Thirty articles ultimately met inclusion criteria. Articles were subdivided into those addressing biomarkers with proven clinical utility and potential biomarkers which have future application.

CONCLUSIONS: Biomarkers have been identified which can help to determine the effect of DBS on patients with PD. Current studies demonstrate there are measured differences in electrophysiological oscillations, gene expression, neuropeptide levels, metabolic function, inflammatory activity and others in the CNS after DBS in PD. Currently, local field potential, beta-band analysis stand as the clinically proven biomarkers of choice for DBS in PD. Many of the identified changes noted could potentially be implemented as clinically useful biomarkers through which DBS may be monitored. Future studies are needed to determine which noted physiological changes are most appropriately used as biomarkers and in what contexts they are most helpful.