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.