Fifteen-year follow-up of 92 hospitalized adults with Down's syndrome: incidence of cognitive decline, its relationship to age and neuropathology.

BACKGROUND: The clinical and neuropathological features associated with dementia in Down's syndrome (DS) are not well established. Aims To examine clinico-pathological correlations and the incidence of cognitive decline in a cohort of adults with DS. METHOD: A total of 92 hospitalized persons with DS were followed up from 1985 to December 2000. At outset, 87 participants were dementia-free, with a median age of 38 years. Assessments included the Prudhoe Cognitive Function Test (PCFT) and the Adaptive Behavior Scale (ABS), to measure cognitive and behavioural deterioration. Dementia was diagnosed from case records and caregivers' reports. RESULTS: Eighteen (21%) patients developed dementia during follow-up, with a median age of onset 55.5 years (range 45-74). The PCFT demonstrated cognitive decline among those with a less severe intellectual disability (mild and moderate) but not among the profoundly disabled people (severe and profound). Clinical dementia was associated with neuropathological features of Alzheimer's disease, and correlated with neocortical neurofibrillary tangle densities. At the age of 60 years and above, a little more than 50% of patients still alive had clinical evidence of dementia. CONCLUSIONS: Clinical dementia associated with measurable cognitive and functional decline is frequent in people with DS after middle age, and can be readily diagnosed among less severely intellectually disabled persons using measures of cognitive function such as the PCFT and behavioural scales such as the ABS. In the more profoundly disabled people, the diagnosis of dementia is facilitated by the use of behavioural and neurological criteria. In this study, the largest prospective DS series including neuropathology on deceased patients, the density of neurofibrillary tangles related more closely to the dementia of DS than senile plaques. In people with DS surviving to middle and old age, the development of dementia of Alzheimer type is frequent but not inevitable, and some people with DS reach old age without clinical features of dementia.

The Prudhoe Cognitive Function Test, a scale to assess cognitive function in adults with Down's syndrome: inter-rater and test-retest reliability.

BACKGROUND: The Prudhoe Cognitive Function Test (PCFT) was designed to measure cognitive function in subjects with all degrees of intellectual disability (ID) and to be administered by non-specialist raters. The aim of the present study was to measure the test-retest and inter-rater reliability of the PCFT. METHODS: Three raters, one a specialist and two non-specialists, administered the PCFT to 14 subjects with Down's syndrome on two occasions separated by 4 weeks. RESULTS: The intra-class correlation coefficients (ICCs) between the rater pairs (n=3) were 0.99, 0.99 and 0.98 (P<0.01). Floor effects were recorded for two items. The ICC for test-retest reliability was 0.99 (P<0.01). CONCLUSIONS: The PCFT is a highly reliable instrument when used by either specialist or non-specialist raters. It has excellent temporal stability.

Preliminary evaluation of a scale to assess cognitive function in adults with Down's syndrome: the Prudhoe Cognitive Function Test.

BACKGROUND: In the clinical diagnosis of dementia in Down's syndrome (DS), it may be difficult to distinguish between cognitive deterioration and the various degrees of pre-existing intellectual disability (ID). Serial measurements of both cognitive function and behaviour are required. The aim of the present study was to evaluate the performance of non-demented adults with DS on a subject-directed instrument, the Prudhoe Cognitive Function Test (PCFT), preliminary to its serial use in a prospective study. METHODS: From 1985 to 1986, 85 non-demented hospitalized adults with DS were interviewed using the PCFT. The Adaptive Behavior Scale (ABS) was administered to the carers. The subjects' levels of ID (graded from mild through moderate, severe and profound to untestable) were based on their scores on the Stanford-Binet Intelligence Scale, as reported in the medical records, and the relationship between level of disability and performance on the PCFT and ABS, and their respective domains, was examined. RESULTS: Both scales produced a wide range of scores and the correlation between them was highly significant. Both scales correlated highly significantly with the degree of ID, but more subjects with high levels (i.e. profound to untestable) of disability obtained very low or zero scores on the PCFT and its domains than on the ABS. CONCLUSIONS: The PCFT provides a reliable quantitative measure of cognitive function in subjects with DS, and could be a useful adjunct to the diagnosis of dementia in prospective studies. However, the almost uniformly low scores obtained by those with high levels of ID suggests that its power to detect cognitive decline will be limited to those who are less disabled, while the ABS may be more useful than the PCFT in detecting deterioration in people with profound ID.