Cognitive performance and neuropsychiatric symptoms in early, untreated Parkinson's disease

This study was undertaken to determine the prevalence and correlates of cognitive impairment (CI) and neuropsychiatric symptoms (NPS) in early, untreated patients with Parkinson's disease (PD). Background: Both CI and NPS are common in PD and impact disease course and quality of life. However, limited knowledge is available about cognitive abilities and NPS. Methods: Parkinson's Progression Markers Initiative (PPMI) is a multi-site study of early, untreated PD patients and healthy controls (HCs), the latter with normal cognition. At baseline, participants were assessed with a neuropsychological battery and for symptoms of depression, anxiety, impulse control disorders (ICDs), psychosis, and apathy. Results: Baseline data of 423 PD patients and 196 HCs yielded no between-group differences in demographic characteristics. Twenty-two percent of PD patients met the PD-recommended screening cutoff for CI on the Montral Cognitive Assessment (MoCA), but only 9% met detailed neuropsychological testing criteria for mild cognitive impairment (MCI)-level impairment. The PD patients were more depressed than HCs (P<0.001), with twice as many (14% vs. 7%) meeting criteria for clinically significant depressive symptoms. The PD patients also experienced more anxiety (P<0.001) and apathy (P<0.001) than HCs. Psychosis was uncommon in PD (3%), and no between-group difference was seen in ICD symptoms (P=0.51). Conclusions: Approximately 10% of PD patients in the early, untreated disease state met traditional criteria of CI, which is a lower frequency compared with previous studies. Multiple dopaminergic-dependent NPS are also more common in these patients compared with the general population, but others associated with dopamine replacement therapy are not or are rare. Future analyses of this cohort will examine biological predictors and the course of CI and NPS.