Objective: To determine the prevalence of dementia in an Irish sample of Down's syndrome (DS) patients and to examine the utility of a number of cognitive and functional scales in the assessment of dementia in this population.
Method: 76 DS patients diagnosed clinically (range 33–72 years; mean age 47.3 ± 8.8 years) were included in the study. The diagnosis of dementia was made on clinical grounds using DSMIIIR criteria. Cognitive and functional impairment were evaluated using the following scales; Test for Severe Impairment (TSI), Down's Syndrome Mental Status Examination (DSMSE), Daily Living Skills Questionnaire (DLSQ), and the Mental State Performance (MSP).
Results: The overall prevalence of dementia was 7.9% (95% C.I = 2.95–16.39). The presence of dementia was associated with late onset epilepsy, anticonvulsant medication and deafness. Standard cognitive tests such as the MSP showed an early ‘floor’ effect in this population. In contrast the TSI and DLSQ showed a satisfactory range of scores in these patients with moderate to severe learning disability.
Conclusions: The low prevalence of dementia in this study may be explained by the strict conservative criteria applied in the clinical diagnosis. Prospective assessment of DS patients on a longitudinal basis using decline on scales such as the TSI and DLSQ may allow more accurate diagnosis of dementia at an earlier stage in this at-risk population.