Cognitive decline in ageing: are AAMI and AACD distinct entities?

Background: Two sets of research diagnostic criteria, age-associated memory impairment (AAMI) and ageing-associated cognitive decline (AACD), are widely used to describe mild cognitive decline in ageing. However, the extent to which the nosological entities they represent are similar or distinct is unclear.

Methods: A sample of 111 participants without dementia but with informant evidence of cognitive decline were drawn from the EUGERIA Study of Cognitive Ageing, a population-based study in southern France. These participants were classified as either normal or with AAMI according to the criteria of Crook et al. (1986), then reclassified as normal or with AACD according to criteria recommended by Levy et al. (1994). Neuropsychological test scores were then compared in these two pairs of groups.

Results: Particpants were classified as either normal (N=74) or with AAMI (N=37), then reclassified as normal (N=72) or with AACD (N=39). Only 20 (54%) of participants with AAMI simultaneously met criteria for AACD, and those with AACD showed more extensive cognitive impairment than those with AAMI.

Conclusions: Although there is a large overlap between AAMI and AACD, these findings suggest that AAMI and AACD refer to distinct clinical entities, the latter delineating a more severe state of impairment. This may be largely because AAMI is defined as impairment with reference to young normals, whereas AACD refers to impairment with respect to normal contemporaries.