Optimizing the selection of Parkinson's disease patients for neuromodulation using the levodopa challenge test.

Background: In Parkinson's disease (PD), early stages are associated with a good long-duration response and as the disease advances, the short-duration response predominates. The transition between the long-duration and short-duration responses may be an important and measurable intermediate stage. A critical criterion in determining the candidature for neuromodulation is a beneficial response to an 'off-on' levodopa challenge test. This test is usually reserved for those that have already developed marked short-duration response and are candidates for deep brain stimulation (DBS) surgery. However, identifying those that are in transition may allow DBS to be offered earlier.

Objective: The objective of the study was to determine if the transition from a long-duration to a short-duration response can be assessed on a levodopa challenge test.

Methods: An 'off-on" levodopa challenge test was done in sixty-five PD patients divided into four groups based on the disease duration.

Results: OFF motor scores increased in all groups [Mean ± STD; 22.94 ± 8.52, 31.53 ± 9.87, 34.05 ± 9.50, and 33.92 ± 10.15 in groups 1-4, respectively] while a significant response to medication was maintained on 'off-on' testing. The mean levodopa equivalency dose in groups 1 and 2 was significantly less than in groups 3 and 4. This transition occurred between years 7 and 9 of disease duration.

Conclusion: Performing a regular levodopa challenge test, when levodopa dose increases substantially, should be considered to determine the ideal time for DBS in patients with Parkinson's disease.