Subjective Cognitive Complaints Signal Potential Cognitive Decline in Parkinson Disease

A newly published meta-analysis in Movement Disorders showed that subjective cognitive complaints (SCCs) in patients with and without objective cognitive impairment are frequent, occurring in more than one-third of those with Parkinson disease (PD). These findings suggest SCCs might represent a potential risk marker of subsequent cognitive decline in patients living with PD.¹

In the meta-analysis, investigators observed an SCC prevalence of 36% (n = 2350; 95% CI, 30%-42%) with a high heterogeneity (Q = 162.12; P <.001; I2 = 88.28%) in patients with PD (n = 3441). Authors noted that this prevalence was moderated significantly by study heterogeneity regarding female sex, disease severity, levodopa equivalent daily dosage, exclusion from the overall sample of patients with objective cognitive impairment, and measurement instrument.

“Therefore, even in cases where there was no evidence of objective cognitive impairment and subjective changes in cognitive abilities might be thought to reflect neuropsychiatric symptoms in PD, the possibility of subsequent cognitive deterioration should not be excluded, and patients with SCCs must still be monitored for change and functional impact in PD,” lead author Mattia Siciliano, PsyD, PhD, professor of psychology at the University of Campania “Luigi Vanvitelli”, in Caserta, Italy, and colleagues wrote.¹ “In this regard, the early identification and treatment of neuropsychiatric symptoms in clinical care might help address the SCCs and increase the likelihood to prevent the cognitive decline.”

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Investigators selected 31 studies from 204 abstracts up to June 2023 in PubMed, Scopus, Web of Science, and PsycINFO (ProQuest) for the meta-analysis. Of these studies, 15 included patients with objective cognitive impairment and 16 included cognitively unimpaired patients. In the 31 studies, 20 reported the SCC prevalence, 28 explored the cross-sectional association between SCCs and cognitive changes on objective testing or neuropsychiatric symptoms, 21 investigated the association between SCCs and cognitive changes on objective testing in addition to the association between SCCs and neuropsychiatric symptoms, and 5 reported the risk of SCCs to progress to objective cognitive decline.

Further in the analysis, authors noted that SCC prevalence showed no difference between de novo and treated patients with PD. Investigators also observed that SCCs were weakly and negligibly associated with cognitive changes on objective testing in patients from the cross-sectional studies. In contrast, researchers noted that SCCs had a risk ratio of 2.71 for later cognitive decline over a mean follow-up of 3.16 years in cognitively healthy patients. Additionally, SCCs were moderately related to the co-occurrence of neuropsychiatric symptoms such as depression, anxiety, or apathy. Overall, authors noted that SCCs were more strongly related to these neuropsychiatric symptoms compared with objective cognitive functioning.

This study was limited to English-language articles in the literature review and focused only on patient-reported SCCs. Authors noted that some results require a cautious approach to interpretation because of the high degree of heterogeneity among studies included in the analysis. Furthermore, investigators recommended additional research on the finding concerning the predictive value of SCCs for future cognitive impairments since it was derived from a limited amount of reports that differed in the measurement of SCCs, follow-up duration, and assessment of cognitive performance. The researchers also noted that this meta-analysis was not registered under as an international prospective register of systematic reviews (eg, PROSPERO).²

“In the future perspective, there is a need for recommendations and consensus on how to define and classify SCCs in PD, as different types of SCCs (eg, complaints related to slow thinking, attentive difficulties, or memory) may be differently related to the risk of subsequent objective cognitive decline,” Siciliano et al noted.¹ “In this context, our meta-analysis emphasizes the monitoring of SCCs as a mandatory step in PD assessment to ensure this symptom is not missed in clinical practice and subsequently managed with adequate protocols.

REFERENCES
1. Siciliano M, Tessitore A, Morgante F, Goldman JG, Ricciardi L. Subjective Cognitive Complaints in Parkinson's Disease: A Systematic Review and Meta-Analysis. Mov Disord. 2024;39(1):17-28. doi:10.1002/mds.29649
2. Booth A, Clarke M, Dooley G, et al. The nuts and bolts of PROSPERO: an international prospective register of systematic reviews. Syst Rev. 2012;1:2. Published 2012 Feb 9. doi:10.1186/2046-4053-1-2