The cognition and emotional well-being indices of the Parkinson's disease questionnaire-39: what do they really measure?

Abstract

Introduction: The Parkinson's disease questionnaire-39 (PDQ-39) is a common measure of health related quality of life (HRQoL) that is widely used with Parkinson disease (PD) patients. Previous evidence suggests that the PDQ-39 reflects at least 8 dimensions (i.e., Emotion, Cognitions, Mobility, etc). To date, little research has examined the external/convergent validity of the Cognitions and Emotional Well-being domains of the PDQ-39.

Methods: A convenience sample of 303 PD patients underwent a comprehensive multi-domain neuropsychological evaluation, including tests of execution function, episodic verbal memory, processing speed, language and working memory, as well as completing measures of depression, apathy, state and trait anxiety and HRQoL (PDQ-39). Hierarchical regressions were conducted in order to examine the relationship between scores on neuropsychological tests and the Cognitions index, as well as mood measures and the Emotional Well-being index of the PDQ-39.

Results: Neuropsychological test performance did not account for a significant amount of variance in the PDQ-39 Cognitions index scores. Instead, it was depression that significantly contributed to the Cognitions index, above and beyond neuropsychological performance. The PDQ-39 Emotional Well-being index was also related to mood measures, primarily depression and trait anxiety.

Conclusions: The PDQ-39 Cognition index may be more related to mood functioning, as opposed to cognitive functioning, and should not be considered a "proxy" for cognitive functioning. Future studies are needed to better explain the construct of this index.

Keywords: Cognition; Depression; Health related quality of life; Parkinson's disease.