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

Cognitive impairment and neuropsychiatric symptoms (NPS) are frequent in patients with Parkinson disease (PD), negatively impacting patients’ quality of life and increasing caregiver burden.1 Approximately 25% of non-demented PD patients have mild cognitive impairment (MCI),2 and up to 80% of all PD patients will eventually develop dementia.3 Psychosis, depression, anxiety, apathy, and impulse control disorders (ICDs) are the most frequent and problematic NPS.1 To what extent cognitive impairment and NPS are attributable to the neurodegenerative process, psychosocial, demographic or clinical factors, or a complication of dopamine replacement therapy (DRT) is unclear. The contribution of each factor may differ by disease stage and other variables. To better understand cognition and NPS in PD, patients need to be studied soon after diagnosis, before initiation of DRT. Preliminary studies have shown that a significant percentage (10%–30%) of new (sometimes treated) PD patients have cognitive deficits at rates higher than healthy controls (HCs).4–8 Others have shown that a range of NPS are more common in early PD patients compared with HCs,8–10 with non-motor symptoms predominating in 25% of newly diagnosed, untreated patients.11 The Parkinson’s Progression Markers Initiative (PPMI) is the largest ongoing, prospective, longitudinal study of early untreated (at enrollment) PD patients and HCs.12 Here we report the frequency and correlates of cognitive impairment (CI) and NPS at baseline.