Background: Frailty can lead to increased vulnerability in older people and patients with Parkinson's disease (pwPD) and worsen their health conditions. These patients can also develop cognitive function impairment. The objective is to analyze whether there is a relationship between frailty and cognitive impairment in pwPD, and to find out which instruments to use for its evaluation.

Methods: Publications were searched in PubMed, Medline, Web of Science, Cinalh, Cochrane Library, Embase, Phycinfo, and Scopus. The results were measured with the instruments that are used to assess frailty and cognitive impairment, and analyze their relationship.

Results: Two hundred seventy-one articles were identified, of which 12 met the inclusion criteria. All studies assessed frailty and cognitive function in pwPD. Five studies analyzed the relationship between frailty and cognitive impairment. The most used instruments were the Fried scale followed by the Clinical Frailty Scale (CFS) for frailty. Cognitive impairment was mostly evaluated with the Mini-Mental State Examination and the Montreal Cognitive Assessment. The prevalence data ranged from 20.2 to 51.5% with the Fried scale and from 35.6 to 83.9% with the CFS. Cognitive impairment was present in 15 to 45.2% of the pwPD.

Conclusion: Analysis of the included studies shows a relationship between frailty and cognitive impairment in pwPD. There was significant variability in the application of the scales used, which influences the prevalence data. More observational and experimental studies are needed to provide more evidence on this association and to determine which is the optimal tool to identify frailty in pwPD using multidimensional scales.