| Summary: | <h4>Background</h4>Depression is common in Parkinson's disease (PD). It is however unclear when and how depressive symptoms develop and progress in the course of PD development.<h4>Objective</h4>To assess how depressive symptoms evolve in PD, using repeated measures.<h4>Methods</h4>In 2994 older adults, ages 70-79 years, depressive symptoms were assessed 8 times over 11 years using the 10-item Center for Epidemiologic Studies Depression Scale (CESD-10). For each PD patient at each time point, we calculated the difference between CESD-10 score and its expected value estimated based on data from individuals without PD, and then realigned the time scale in reference to the year of PD diagnosis. We examined longitudinal changes in CESD-10 scores before and after PD diagnosis using a joint modeling approach to account for competing risks of non-participation and death.<h4>Results</h4>A total of 79 PD patients were identified at enrollment or during the follow-up, with repeatedly assessed depressive symptom data up to 9 years before and after PD diagnosis. We found a monotonic trend of increasing CESD-10 score in PD patients throughout the observational period (p = 0.002). The observed scores became higher than expected approximately 7 years before PD diagnosis and significantly different 1 year before PD diagnosis.<h4>Conclusions</h4>Increasing depressive symptomatology appears to precede PD diagnosis by a few years.
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