Comparison of rating scales for the diagnosis of dementia in adults with Down's syndrome.

Making a diagnosis of dementia, particularly in its early stages, in a person with intellectual disability can be difficult Some neuropsychological tests which were originally devised for the diagnosis of dementia in the non-intellectually disabled population have been modified for use in people with intellectual disability. Observer-rated scales have also been used for making a diagnosis of dementia in people with intellectual disability. Within the context of a genetic study, the rates of diagnosis of dementia according to different criteria, namely the clinician's diagnosis (ICD-10), the Dementia Questionnaire for Persons with Mental Retardation (DMR), the Dementia Scale for Down Syndrome (DSDS) and the Mini Mental State Examination (MMSE), were compared among 62 adults with Down's syndrome (26 demented and 36 non-demented adults according to the clinician's diagnosis). A comparison between the clinician's diagnosis and the diagnosis according to DMR criteria showed specificity and sensitivity at the 0.92 level for both categories. Similarly, a comparison between the clinician's diagnosis and the diagnosis according to the DSDS criteria showed a specificity of 0.89 and a sensitivity of 0.85. A good positive correlation was also shown between the scores of the DSDS and the DMR (Pearson's r = +0.868, P < 0.001). A similar positive correlation was found between the overall DSDS score and the scores in the main subcategories of the DMR. An MMSE could be performed in only 34 (55%) out of the 62 subjects with Down's syndrome. Out of the 30 subjects who had an MMSE score of less than 24 (the usual cut-off for the diagnosis of possible dementia), 23 (77%) did not have a diagnosis of dementia according to any criteria. It seems that the observer-rated scales, rather than the direct neuropsychological tests, are more useful for the diagnosis of dementia in people with an intellectual disability.