PDSURG: Parkinson's Disease Surgery trial

A large randomised assessment of the relative cost-effectiveness of surgery for Parkinson's disease

The PD SURG trial will evaluate the role of subthalamic (STN) and pallidal (GPi) surgery, by either stimulation or lesioning, compared to medical therapy (with surgical intervention delayed as long as possible) in patients with advanced Parkinson’s Disease (PD) that is not adequately controlled by their current medical treatment. Patients allocated to medical therapy will receive whatever drug treatment is considered appropriate (this may include continuous apomorphine infusion). Although surgery may produce clear and rapid clinical improvements, it is also important to evaluate the safety and long-term effects and cost-effectiveness of the procedure and to use endpoints of relevance to the patient.

PDSURG is a large, simple, “real-life” trial that will determine reliably whether early surgery is more effective and cost-effective than deferred surgery for advanced PD.

An economic evaluation will be undertaken as part of the randomised assessment of surgery for Parkinson’s Disease. The economic evaluation will estimate the incremental cost of subthalamic (STN) surgery compared to medical therapy (with surgical intervention delayed as long as possible). The incremental effectiveness, measured in life years and Quality adjusted life years (QALYs), will also be estimated allowing the overall cost-effectiveness to be assessed. The cost component will collect data on direct medical costs, informal care costs and productivity costs. The economic evaluation will follow the guidelines established by the National Institute for Clinical Excellence (http://www.nice.org.uk) and the US panel on cost-effectiveness (Gold et al.1999).

The main outcome measure for the PDSURG economic evaluation will be the EuroQol EQ-5D (EuroQol, 1990). This will be administered at baseline and by post at 6 months, one year and yearly thereafter. Responses will be given valuations derived from published UK population tariffs (Dolan et al.1995) and the mean number of quality adjusted life years (QALYs) per patient and incremental QALYs will be calculated.

The mean net cost per patient in each trial arm will be obtained and the incremental cost per patient will be calculated, together with associated measures of variance. Missing values will be estimated by imputation from existing data. Incremental cost effectiveness ratios will be estimated by combining the incremental costs of surgery with the incremental QALYs (if there are any). Stochastic variance around the cost-effectiveness ratio will be calculated using Fieller’s theorem (Willan and O’Brien 1996). Non-stochastic uncertainty, such as the future costs of equipment for STN, will be handled by means of sensitivity analyses. Finally, the results will be expressed in terms of a cost-effectiveness acceptability curve, which indicates the likelihood that that the results fall below any given cost-effectiveness ceiling.

The PDSURG  economic data are currently being analysed in order to produce results at one year follow up. The main clinical findings were reported at the collaborators meeting in Birmingham in May 2009.

Publications

Yianni, J, Green AL, McIntosh E, Bittar RG, Joint C, Scott R, Gregory R, Bain PG, Aziz, T (2005) The costs and benefits of deep brain stimulation for patients with dystonia: An initial exploration. Neuromodulation, 8 (3): 155-161.

McIntosh E, Gray AM, Aziz T (2003) Estimating the Costs of Surgical Innovations: The Case for Subthalamic Nucleus Stimulation in the Treatment of Advanced Parkinson's Disease. Mov Disord 18(9):993-9.

Gray AM, McNamara I, Aziz T, Gregory R, Bain P, Wilson J, Scott R (2002) Quality of life outcomes following surgical treatment of Parkinson's Disease. Mov Disord 17(1)68-75.