Screening for and diagnosing dementia in an elderly residential home population : a validation study.

Abstract

Background: With the projected increase in the elderly population and expected rise in the

prevalence of dementia, particularly in low-and-middle-income countries, early case identification

is necessary for planning and delivering clinical services. The effectiveness of

dementia screening depends on the availability of suitable screening tools with good

sensitivity and specificity to confidently distinguish normal age-related cognitive decline

from dementia. The aims of this research study were to report on the prevalence of

cognitive impairment (dementia and Mild Cognitive Impairment-MCI), and to assess the

performance of selected screening tools and a neuropsychological battery of tests in a

heterogeneous local population.

Methodology

A cross-sectional study was conducted in a heterogeneous elderly South African population

and consisted of three stages of data collection. In the first stage, cognitive screening

measures were administered to a group of 302 participants, aged +60 years, living in a

residential facility for the aged. The second stage consisted of a sub-sample of 140

participants who were assessed for cognitive impairment based on the Diagnostic and

Statistical Manual of Mental Disorders 4th Edition-Text Revised criteria (DSM-IV-TR). Criteria

A and B for Alzheimer’s and Vascular dementia were applied to assign a diagnosis of

dementia without reference to aetiology. The participants were also assessed for Mild

Cognitive Impairment (MCI), based on the criteria of the International Working Group on

Mild Cognitive Impairment. Of the 140 participants in stage two, 117 were administered a

neuropsychological battery of tests in the third stage. The influence of demographic

variables and the sensitivity, specificity and optimum cut-off scores were determined for the

following seven selected screening measures, individually and in combination: the Mini-

Mental State Examination (MMSE), Subjective Memory Complaint (SMC), Subjective

Memory Complaint Clinical (SMCC), Subjective Memory Rating Scale (SMRS), Deterioration

Cognitive Observee (DECO), Subjective Memory Complaint Clinical (SMCC) and the Clock

Drawing Test (CDT). The sensitivity and specificity of the neuropsychological tests in the

detection of dementia were also determined.

Results

Eleven (7.9%) dementia and 38 (27.1%) MCI cases were diagnosed. Performance on the

screening measures was influenced by race, age and education. Using ROC analyses, the

SMCC, MMSE and CDT were found to be moderately accurate in screening for dementia

with AUC >.70. Neuropsychological test performance was influenced by the age, gender,

race and education level of participants. With the exception of the Digit Span (forward),

Digit Span (total), COWAT-A, Narrative Memory Test (delayed recall), Token Test and the

Luria Hand Sequence Test, all the neuropsychological test measures displayed significance in

distinguishing between the three classification groups (controls, MCI, dementia).

Conclusion

SMCC’s are valid screening questions as a first level of ‘rule-out’ screening. The MMSE can

be included at a second stage of screening at general hospital level and the CDT in specialist

clinical settings. Several measures from the neuropsychological battery of tests evaluated

have discriminant validity and diagnostic accuracy for the differential diagnosis of cognitive

disturbances in an elderly heterogeneous South African population .