Interpretation of health-related quality of life outcomes in Parkinson's disease from the EARLYSTIM Study.

The EARLYSTIM Study compared deep brain stimulation (DBS) with best medical treatment (BMT) over 2-years, showing a between-group difference of 8.0 from baseline in favor of DBS in health-related quality of life (HRQoL), measured with the PDQ-39 SI (summary index). This study obtained complementary information about the importance of the change in HRQoL as measured by the PDQ-39, using anchor-based (Patient Global Impression of Change, PGIC) and distribution-based techniques (magnitude of change, effect size, thresholds, distribution of benefit) applied to the EARLYSTIM study data. Anchor-based techniques showed a difference follow-up-baseline for patients who reported "minimal improvement" of -5.8 [-9.9, -1.6] (mean [95%CI]) in the DBS group vs -2.9 [-9.0, 3.1] in the BMT group. As the vast majority (80.8%) of DBS patients reported "much or very much improvement", this difference was explored for the latter group and amounted to -8.7 for the DBS group and -6.5 in the BMT group. Distribution-based techniques that analyzed the relative change and treatment effect size showed a moderate benefit of the DBS on the HRQoL, whereas a slight worsening was observed in the BMT group. The change in the DBS group (-7.8) was higher than the MIC (Minimally Important Change) estimated value (-5.8 by the anchor; -6.3 by triangulation of thresholds), but not in the BMT (0.2 vs. -3.0 to -5.4, respectively). Almost 90% of the patients in the DBS group declared some improvement (58.3% and 56.7% beyond the estimated MIC), which was significantly different from the BMT group whose proportions were 32.0% and 30.3%, respectively. The number needed to treat to improve ≥1 MIC by DBS vs BMT was 3.8. Change in depression, disability and pain influenced the improvement of the DBS group. DBS improved HRQoL in a high proportion of patients to a significant and moderate degree, at 2 years follow-up.