Abstract
INTRODUCTION: Depression can be an intrinsic part of neurodegeneration, or a reaction to the onset of motor or non-motor disability. Depression can also adversely influence an individual's perception of their disease, independently of its severity or impact on function. Participant-reported outcome measures are recognised as an important adjunct to objective clinical trial data. Although severe depression is a frequent contraindication for trial participation, mild-to-moderate depressive symptoms could potentially influence the outcome of such questionnaires. We aimed to explore this within two interventional trials for Parkinson's disease (Exenatide PD3; NCT04232969) and multiple system atrophy (Exenatide MSA; NCT04431713). METHODS: Prior to investigational drug exposure, participants completed either the Patient Health Questionnaire or Beck Depression Inventory-II, which allowed us to dichotomise them into two groups (normal or mild-to-moderately elevated burden of depressive symptoms). Participants with Parkinson's self-completed the Movement Disorder Society Sponsored Revision of the Unified Parkinson's disease Rating Scale Parts 1b and 2, Parkinson's Disease Questionnaire-39, Non-motor Symptoms Scale and EQ-5D-5L, while participants with multiple system atrophy self-completed a Quality of Life scale and had assistance with completing the Unified Multiple System Atrophy Rating Scale Part 1. The Movement Disorder Society Sponsored Revision of the Unified Parkinson's Disease Rating Scale Part 3 and Unified Multiple System Atrophy Rating Scale Part 2 provided objective, clinician-rated measures of motor severity. RESULTS: A mild-to-moderately elevated burden of depressive symptoms was identified in 32.5% (63/194) and 42.0% (21/50) of Parkinson's and multiple system atrophy participants, respectively. Despite the normal and elevated groups being comparable in terms of disease duration and objective motor severity, those with a mild-to-moderately elevated burden of depressive symptoms self-reported worse disease impact. However, measures which involved clinician and/or carer input (Unified Multiple System Atrophy Rating Scale Part 1) were not influenced by co-existing depressive symptoms. CONCLUSIONS: Mild-to-moderate depressive symptoms, below the threshold for diagnosing a depressive disorder, are associated with negative self-reporting, and such findings should be carefully considered when planning the design and analysis of trials in neurodegenerative diseases.