Comparison of characteristics of people with subjective cognitive impairment vs. mild cognitive impairment vs. dementia: cross-sectional data from the Hong Kong Alzheimer’s Disease Association

Abstract

BACKGROUND: The preclinical phase of dementia is defined as when there is subjective cognitive impairment (SCI) but no obvious abnormality on basic cognitive testing or limitation on daily activities. From a clinico-pathological perspective, this SCI phase precedes the onset of mild cognitive impairment (MCI - abnormal cognitive function but no limitation on daily activities) and dementia (abnormal cognitive function plus limitation on daily activities). We conducted a large cross-sectional study to determine the characteristics of people with SCI, compared with those with MCI and dementia. METHODS: We analyzed the data of 941 help-seekers who sought assessment between 2005-2013 at a community-based, territory-wide screening program for dementia, operated by the Hong Kong Alzheimer’s Disease Association. Based on a MMSE cut-off score of 23 (out of 30), a Barthel Index cut-off score of 90 (out of 100), and presence of subjective memory complaint, we classified 941 patients (70% females, mean age 77±8 years) into three groups: SCI (n=227), MCI (n=628), and suspected dementia (n=86). Informants to the patient included their children (81%), spouses (9%), in-laws (6%) and grandchildren (3%). RESULTS: Mean MMSE was higher for participants with SCI compared with MCI and dementia groups (26±2 vs.16±4 vs.13±4), as was mean Barthel Index (99±2 vs. 98±3 vs. 72±18) and level of independence (Lawton’s IADL 51±6 vs. 43±10 vs. 22±10). All the major cognitive domains showed significant decline from SCI to MCI to dementia. In terms of characteristics, participants with SCI were significantly (vs. MCI and dementia groups): younger (72±9 vs. 78±7 vs. 82±6 years); more likely to receive no or up to primary education (52% vs. 79% vs. 85%); take less time to seek help (mean delay 21±20 vs. 23±19 vs. 32±47 months); less likely to have heart disease (21% vs. 59% vs. 20%) or stroke (19% vs. 55% vs. 26%); lower Geriatric Depression Score (3.3±3.1 vs. 3.5±3.1 vs. 4.5±3.2); and more like to fall (0.19±0.5 vs. 0.21±0.5 vs. 0.42±0.58). All significant results had p<0.05. There was no significant difference in the history of diabetes mellitus or hypertension between the 3 groups. CONCLUSION: Our study revealed significant differences in the characteristics between people with SCI, MCI and dementia. A higher education level may facilitate earlier help-seeking, and progressively more severe cognitive decline was associated with higher levels of disability and depression. This SCI phase may provide an opportunity for therapeutic strategies and prevention of further cognitive decline, hence large scaled longitudinal and intervention studies are warranted.