• cognitive impairment;
  • dementia;
  • developing countries;
  • Thailand;
  • screening test

Background:  We conducted a population-based prospective study in 420 older persons to examine the prevalence of undiagnosed dementia and validity of the Chula Mental Test (CMT) as well as value of serial administration of the CMT and its score evolution over 2 years.

Methods:  The CMT score was obtained in 1997 and 1999 surveys. In 1999, all participants were evaluated by a geriatrician to make diagnoses of dementia according to the 4th edn of the Diagnostic and Statistical Manual criteria. Information on previous diagnosis of dementia by physicians was collected. Validity of the CMT was determined by the receiver–operator curve. The pattern of cognitive evolution over 2 years was analyzed.

Results:  Of 420 subjects, 23 had dementia, of which 22 (95.6%) were undiagnosed. The prevalence (95% confidence interval) of dementia and undiagnosed dementia were 5.5% (3.3–7.7%) and 5.3% (4.1–6.3%), respectively. With original cut-off (15/14) of the CMT, the sensitivity and specificity were 0.74 and 0.86, respectively. The best cut-off found in this study was 16/15 which provided better sensitivity (0.91) but worse specificity (0.76) than those of the original cut-off. Pattern of cognitive evolution was heterogeneous. The heterogeneous change was substantial in subjects with mild low CMT score. Cognitive evolution pattern showed that serial administration of the CMT could reduce workload of primary care physicians and might be useful in a screening protocol.

Conclusion:  The prevalence of undiagnosed dementia in community-dwelling Thai older persons was high. The CMT was valid for use in a community. Heterogeneous evolution of cognitive function and value of serial cognitive impairment screening was found.