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Progression of Cognitive Decline in Parkinson's Disease
Mandy Roheger1, Elke Kalbe1, Inga Liepelt-Scarfone2,3
1Medical Psychology I Neuropsychology and Gender Studies and Center for Neuropsychological Diagnostics and Intervention (CeNDI), University Hospital Cologne, Köln, Germany.
Background:
Cognitive dysfunction is one of the most prevalent non-motor symptoms in Parkinson's disease (PD), often experienced as more debilitating for patients and caregivers than motor problems. Therefore, a deeper understanding of the course of cognitive decline and the identification of valid progression markers for Parkinson's disease dementia (PDD) is essential.
Objective:
This systematic review summarizes the current state of knowledge on cognitive decline over time by reporting effect sizes of cognitive changes in neuropsychological tests.
Methods:
1368 studies were identified by a PubMed database search and 25 studies by additionally scanning previous literature. After screening all records, including 69 full-text article reviews, 12 longitudinal studies on the progression of cognitive decline in PD met our criteria (e.g., sample size ≥50 patients).
Results:
Only a few studies monitored cognitive decline over a longer period (>4 years). Most studies focused on the evaluation of change in global cognitive state by use of the Mini-Mental State Examination, whereas the use of neuropsychological tests was highly heterogenic among studies. Only one study evaluated patients' cognitive performance in all specified domains (executive function, attention & working memory, memory, language, and visual-spatial function) allowing for diagnosis of cognitive impairment according to consensus guidelines. Medium to strong effect sizes could only be observed in studies with follow-up intervals of four years or longer.
Conclusions:
The results emphasize the need for the assessment of larger PD cohorts over longer periods of follow-up with a comprehensive neuropsychological battery.