Mild cognitive impairment in a community sample: the Sydney Memory and Ageing Study

Area of Science:

• Gerontology
• Neurology
• Epidemiology

Background:

• Mild cognitive impairment (MCI) is a significant risk factor for dementia.
• Understanding MCI subtypes, progression, and stability is crucial for early intervention and dementia prevention strategies.

Purpose of the Study:

• To determine the incidence rates of various Mild Cognitive Impairment (MCI) subtypes.
• To investigate the progression rates of MCI to dementia.
• To assess the stability of MCI classification over a two-year period.

Main Methods:

• A population-based longitudinal study, the Sydney Memory and Ageing Study, followed 873 community-dwelling adults aged 70-90 years for two years.
• Neuropsychological testing across five cognitive domains was used to diagnose no cognitive impairment, MCI, or dementia.
• Standardized diagnostic criteria were applied to classify cognitive status.

Main Results:

• The overall incidence of MCI was 104.6 per 1000 person-years, notably higher in men (156.8) than women (70.3).
• Incidence rates varied by subtype: amnestic MCI (single-domain 47.7, multiple-domain 7.9) and nonamnestic MCI (single-domain 45.0, multiple-domain 3.9).
• The 2-year progression to dementia from MCI was 4.8%, highest in multidomain amnestic MCI (9.1%), with 28.2% of MCI cases reverting to normal cognition.

Conclusions:

• MCI incidence, particularly for single-domain and in men, is higher than previously reported.
• Multidomain amnestic MCI presents the highest risk for dementia progression.
• The diagnosis of MCI, especially single-domain MCI, demonstrates significant instability, highlighting the need for careful diagnostic interpretation.