An application study: 21-item Subjective Cognitive Decline Questionnaire in detecting mild cognitive impairment

BackgroundSubjective cognitive decline (SCD) is a common early complaint in mild cognitive impairment (MCI). Evidence for the 21-item SCD-Questionnaire (SCD-Q21) to discriminate MCI from normal controls (NCs) is limited.ObjectiveTo investigate the discrimination performance of Chinese SCD-Q21 and compare it with SCD-Q9 for community-based MCI early detection, assess the added value of simple covariates, and determine an optimal SCD-Q21 cut-off.Methods294 NCs and 83 people with MCI were assessed and collected demographic and clinical data. Participants completed SCD-Q21, SCD-Q9, Hamilton Anxiety Scale (HAMA) and Hamilton Depression Scale (HAMD) scale; clinical adjudication used Montreal Cognitive Assessment-Basic, Clinical Dementia Rating, and Activities of Daily Living. Group comparison, logistic regression and ROC analyses were applied. Optimal cut-offs were derived using the Youden index and AUCs were compared using DeLong tests. Within-MCI analyses contrasted screen-positive versus screen-negative subgroups.ResultsTotal SCD-Q21 scores were higher in MCI, although five items [question 1 (Q1), Q2, Q3, Q11, and Q17] did not differ between groups. In multivariable binary logistic regression models, lower education (OR = 0.786), higher body mass index (BMI) (OR = 17.874), and higher SCD-Q21 total scores (OR = 1.114) were independently associated with MCI, whereas SCD-Q9 was not. Standalone AUCs were 0.662 (SCD-Q21) and 0.640 (SCD-Q9). Combing age, sex, education, BMI, and HAMA/HAMD with SCD instrument yielded AUC ∼0.91. SCD-Q21 ≥ 7 gave 69.88% sensitivity and 62.93% specificity. Screen-negative MCI cases showed lower vascular/metabolic comorbidity and lower HAMA/HAMD scores.ConclusionsSCD-Q21 provides independent information but modest stand-alone discrimination. As part of a brief multivariable triage including education, BMI, vascular risk review, and anxiety rating, it supports efficient case-finding in community settings.