Depression and anxiety are co-morbid but dissociable in mild Parkinson's disease: A prospective longitudinal study of patterns and predictors

•We examine the course and associations of depression and anxiety in Parkinson's disease over time.•Depressive symptoms remained stable while anxiety symptoms improved over 18 months.•Depression is associated with gender, anxiety, apathy and motor fluctuations.•Anxiety is associated with age, education, disease duration, age of onset and daytime sleepiness.

BackgroundDepression and anxiety are common in Parkinson's disease (PD) and contribute significantly to a reduced quality of life in PD patients. Though they often co-exist, it is unclear whether depression and anxiety result from a shared pathological process. We studied the longitudinal course and determinants of depression and anxiety in PD in order to understand which factors contribute to the development of these symptoms.MethodsWe conducted a prospective longitudinal study of 89 mild PD patients over 18 months, measuring depressive and anxiety symptoms at 6 monthly intervals using the Geriatric Depression Scale and Hospital Anxiety and Depression Scale – ‘Anxiety’ subscale. Univariate and multivariate Generalised Estimating Equations were used to investigate the course of depression and anxiety and their association with demographic factors, motor measures, non-motor symptoms, and pharmacological factors.ResultsDepression and anxiety were co-morbid in 13.5% of the sample. Depressive symptoms remained relatively stable while anxiety symptoms improved over the course of 18 months. Severity of depressive symptoms was associated with female gender, motor fluctuations, apathy, and anxiety, while severity of anxiety was associated with older age, higher educational attainment, shorter disease duration, younger age of disease onset, and excessive daytime sleepiness.ConclusionsAlthough depression and anxiety are frequently co-morbid in PD, they were dissociable from each other. They had distinct trajectories and different longitudinal relationships with demographic, motor, and non-motor factors that were unique to each disorder.