Asymmetric responsiveness of disability and health-related quality of life to improvement versus decline in Parkinson's disease.

Abstract

Clinical trials in Parkinson's disease commonly employ outcome measures of disability and quality of life. Responsiveness of these outcomes measures to symptomatic decline versus improvement has not been studied. We wanted to study the responsiveness of Schwab & England Activities of Daily Living Scale (SE) and Short Form-12 (SF-12) to symptomatic decline versus improvement in Parkinson's disease over a 4-year period among a naturalistic cohort of patients. Parkinson's disease patients (N=228, disease duration 6.1years) were followed for 4years with assessments of disease severity, Unified Parkinson's Disease Rating Scale (UPDRS), health-related quality of life (SF-12 physical/mental health), and disability (SE). The sample was subdivided into those who declined (N=118) or improved (N=102) on total-UPDRS. Responsiveness was assessed with Cohen's effect size and standardized response mean. At baseline, patients who improved over 4years had greater disease severity and worse quality of life than decliners (p<.05). Decliners had a 13.5-point worsening on total-UPDRS, 26.3-39.8; p<.001) associated with concomitant decline on the SF-12 (physical health 42.9-39.2, mental health 50.0-46.6; both p<.001) and the SE (85-74%; p<.001). Improvers had a 13.0-point improvement on total-UPDRS (39.8-26.8; p<.001) associated with minimal change on the SF-12 (physical health 40.8-39.5, mental health 47.1-46.3) and SE (79-79%). Based on effect size, the rank order of responsiveness of measures for decliners from high to low was SE (-0.78), Short Form-12 mental health (-0.45), and SF-12 physical health (-0.34). Rank order of responsiveness for improvers was Short Form-12 physical health (-0.11), SF-12 mental health (-0.10), and SE (-0.03). Among decliners, measures of disability and quality of life were moderate to highly responsive to change in disease severity. Among improvers, both disability and quality of life were poorly responsive despite UPDRS improvement of comparable magnitude.