Do Patients with Progressive Supranuclear Palsy Have Episodic Memory Impairment? A Systematic Review.

Background: Progressive supranuclear palsy (PSP) is the most common atypical parkinsonism and has executive dysfunction as a core feature. The magnitude of episodic memory disturbance in PSP is yet to be clarified. Objectives: To investigate how impaired is episodic memory in PSP compared to healthy controls and other neuropsychiatric disorders. Also, we sought to identify the brain correlates underlying these memory disturbances. Methods: We performed a systematic search on PubMed and Scopus, combining the terms "progressive supranuclear palsy" AND "memory". The search was limited to papers published in English, French, Portuguese or Spanish, with no chronological filters. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. Results: The initial search returned 464 results. After extraction of duplicates, 356 records were screened, leading to inclusion of 38 studies. Most studies found that PSP patients had lower scores on episodic memory compared to healthy controls. In addition, the majority of studies suggest that PSP does not differ from Parkinson's disease and from atypical parkinsonism in terms of episodic memory performance. The same is seen for PSP and frontotemporal dementia. Conversely, episodic memory impairment seems to be greater in typical Alzheimer's disease compared to PSP. Neuroimaging findings indicate that striatofrontal structures may be involved in PSP episodic memory dysfunction, while no associations with mesial structures (including hippocampi) were found. Conclusions: Episodic memory is impaired in PSP. Whether this amnesia refers to executive dysfunction is still controversial. More studies are warranted to clarify the neural basis of memory impairment in PSP.