The Parkinson's Disease-Health Index: A novel, disease-specific patient-reported outcome measure

Background In anticipation of future clinical trials involving individuals with Parkinson's disease (PD), it is important to have fully validated, clinically-relevant, responsive, disease-specific patient-reported outcome measures that are capable of serially measuring how an individual with PD feels and functions. Objective To develop and validate a disease-specific patient-reported outcome measure for PD that is sensitive in detecting clinically meaningful changes in multifactorial disease burden during clinical trials. Methods We conducted qualitative interviews and a cross-sectional study to identify the most important symptoms to individuals with PD. Symptom questions with the highest frequency and relative importance to the cross-sectional study cohort were selected for potential inclusion in the Parkinson's Disease-Health Index (PD-HI). The PD-HI was evaluated and refined through: 1) Qualitative beta interviews; 2) Test-retest reliability assessments; 3) Internal consistency analysis; and 4) Cross-sectional subgroup analysis of PD-HI subscale scores. Results Twenty individuals with PD participated in initial qualitative interviews and 404 individuals with PD participated in the cross-sectional study. Symptom questions representing 13 symptomatic themes of PD health were selected for inclusion in the PD-HI. Beta interview participants found the PD-HI to be comprehensive, relevant, and easy to use. The PD-HI demonstrated high test-retest reliability (ICC = 0.90) and internal consistency (α= 0.99). PD-HI total and subscale scores successfully distinguished between subgroups of participants with varying disease severity. Conclusions Initial evaluation of the PD-HI demonstrates its content validity, construct validity, usability, and test-retest reliability as a patient-reported outcome tool for potential use in PD clinical trials.