Early detection of isolated memory deficits in the elderly: the need for more sensitive neuropsychological tests.

BACKGROUND: Early detection of cognitive decline in the elderly is important because this may precede progression to Alzheimer's disease. The aim of this study was to see whether sensitive neuropsychological tests could identify pre-clinical cognitive deficits and to characterize the cognitive profile of a subgroup with poor memory.
METHODS: A neuropsychological test battery was administered to a community-dwelling sample of 155 elderly volunteers who were screened with CAMCOG at enrolment (mean age 74.7 years). The battery included tests of episodic memory. semantic and working memory, language and processing speed.
RESULTS: Episodic memory test z scores below 1 S.D. from the cohort mean identified 25 subjects with non-robust' memory performance. This group was compared to the remaining 'robust memory' group with a General Linear Model controlling for age, IQ, education and gender. Test performance was significantly different in all tests for episodic and semantic memory, but not in tests for working memory, processing speed and language. CANTAB paired associates learning and spatial recognition tests identified the highest percentages of those in the 'non-robust memory group. Processing speed partialled out the age effect on memory performance for the whole cohort, but the 'non-robust memory' group's performance was not associated with age or processing speed.
CONCLUSIONS: Sensitive neuropsychological tests can detect performance below the norm in elderly people whose performance on MMSE and CAMCOG tests is well within the normal range. Age-related decline in memory performance in a cohort of the elderly may be largely due to inclusion within the cohort of individuals with undetected pre-clinical Alzheimer's disease or isolated memory impairment.