Unawareness of deficits in mild cognitive impairment: a systematic review of its role in progression to Alzheimer's disease.

BACKGROUND: Reduced awareness or poor insight into cognitive abilities is a well-documented feature of Alzheimer's disease, yet its role in the earlier stages of cognitive decline-particularly in individuals with mild cognitive impairment (MCI)-remains less clear. Understanding whether diminished awareness in MCI is a predictor of progression to dementia is crucial, as it may help identify individuals who are at greater risk and who could benefit from timely support and intervention. This systematic review evaluates the evidence linking reduced awareness in MCI with an increased likelihood of conversion to dementia.

METHOD: Four electronic databases (CINAHL, Medline, Embase and PsychInfo) were systematically searched for all studies assessing awareness in individuals with MCI, which tracked their cognitive status over time. The protocol was registered with PROSPERO and PRISMA guidelines were followed. Inclusion criteria-studies must: Include participants with confirmed MCI diagnosis; Assess the relationship between awareness of cognitive and/or functional abilities and the development of dementia; Have longitudinal design; Be peer-reviewed. Exclusion criteria-studies must not: Be published in a different language to English; Include participants with comorbid neurological conditions; Include participants from the same cohort as another study; Use a case series design. Eleven studies were identified as fulfilling all criteria. Study quality was evaluated using the Critical Appraisal Skills Programme (CASP) checklist for cohort studies.

RESULTS: Six studies reported a statistically significant association between reduced awareness and conversion to dementia. Four studies found a trend toward significance, suggesting a possible link, but either did not test for significance or failed to reach it. Only one study found no association. Study quality was rated as high in five studies, moderate in two, and low in four. Notably, higher-quality studies were more likely to report significant associations. Due to substantial methodological variability across studies, a meta-analysis was not feasible.

CONCLUSIONS: Reduced awareness of memory impairment appears predictive of increased risk of progression from MCI to dementia. Assessing awareness-through informant reports and/or comparisons between subjective and objective cognitive measures-could help identify individuals at elevated risk. These individuals may benefit from closer monitoring to facilitate timely diagnosis and intervention.