The Validity of Health-Related Quality of Life Instruments in Patients With Late-Stage Parkinson’s Disease

OBJECTIVE: To examine the validity of health-related quality of life (Hr-QoL) measures in patients with late-stage Parkinson’s disease (PD). METHODS: We analysed data from patients with late-stage PD and their carers who were assessed with a range of clinical measures and the EQ-5D-3 L. The DEMQOL-Proxy was completed for 157 patients with a diagnosis of dementia and the PDQ-8 by 401 patients without dementia. Convergent validity was assessed using correlations with measures of Parkinson’s severity, independence and cognitive function, and construct validity using correlations with patients’ own EQ-5D-3 L scores. In addition, we assessed divergent validity using correlations with carers’ own EQ-5D index, EQ-VAS and Zarit caregiver burden scores. RESULTS: In patients without dementia, both the PDQ-8 and EQ-5D-3 L correlated with measures of disease severity, dependence and carer burden scores, and PDQ-8 scores moderately with EQ-5D-3 L and EQ-5D-3 L VAS scores. In patients with dementia, EQ-5D-3 L scores correlated with disease severity, cognition and dependence scores, but DEMQOL-Proxy scores were moderately associated only with patients’ dependence and carers’ own EQ-5D-3 L scores but not patients’ disease severity, EQ-5D-3 L or cognitive scores. CONCLUSIONS: The PDQ-8 and EQ-5D-3 L have adequate validity in late stage PD without dementia, but in those with PD and dementia the EQ-5D-3 L may be preferable to the DEMQOL-Proxy.