Prevalence in ageing-associated cognitive decline in an elderly population.

Introduction

The decline in memory and other cognitive abilities during ageing is well documented [e.g. 1, 2]. However, the diagnostic classifications aimed to characterize elderly individuals with different degrees of cognitive decline (but not demented) are not established. Recently, a working party of the International Psychogeriatric Association (IPA) in collaboration with the World Health Organization (WHO) proposed diagnostic criteria for 'ageing-associated cognitive decline' (AACD) to categorize a group of subjects with cognitive decline falling short of dementia [3]. The criteria include the presence of subjective gradual cognitive decline (for at least 6 months) and objective evidence of abnormal performance in any principal domain of cognition, i.e. memory and learning, attention and concentration, thinking, language or visuospatial functioning. The abnormality is defined as performance at least one standard deviation (SD) below the age and education norms in well standardized neuropsychological tests. Furthermore, there must be no evidence of any medical condition known to cause cerebral dysfunction. Thus, the AACD diagnosis identifies persons with subjective and objective evidence of cognitive decline which does not impair function to warrant a diagnosis of dementia. The criteria leave open the question of progression. For some subjects, AACD may precede dementia, whereas for others it may be a relatively stable condition.

The AACD diagnosis is related to 'age-associated memory impairment' (AAMI), a condition characterized in the criteria proposed by a working group of the National Institute of Mental Health [4]. However, the AAMI diagnosis is based on a less comprehensive evaluation which takes into account memory function only. The AAMI criteria also differ from the AACD criteria in that the subjects are classified as having AAMI if they score 1 SD below the mean of younger adults (not people of their own age) in a standardized memory test. In spite of many supporting reports [5-8] and the high prevalence of AAMI [9], the significance of this condition has remained controversial [10-12].

AACD has to be differentiated also from 'mild cognitive disorder' (MCD), a classification included in the research criteria for ICD-10 by WHO [13]. This diagnosis is used only when there is an indication of a disease or condition known to cause cerebral dysfunction. Yet another related concept is included in DSM-IV [14] as 'age-related cognitive decline' and defined as 'an objectively identified decline in cognitive functioning consequent to the ageing process that is within normal limits given the person's age'.

The purpose of this study was to evaluate the prevalence rate of AACD in a randomly selected sample of elderly people by applying the criteria proposed by the IPA working party. The associations of age, sex and education with prevalence rates were also evaluated. Furthermore, we examined the diagnostic value of a neuropsychological test battery for identifying AACD subjects.

Subjects and Methods

A random sample of 592 persons, 68-78 years of age, was drawn from the Kuopio population register. Of these subjects 79 had died and 11 had moved outside the study area before they were contacted. Of the remaining 502 subjects, 403 (80.3%) were evaluated. Of those not participating in the study, 17 were too ill to participate, 55 refused to participate and 27 could not be contacted. The study population has been described previously as a part of a report on the prevalence of AAMI [9]. The mean age of the participants was 71.3 years (SD 3.1, range 68-78). Women were somewhat older than men (71.9 vs. 71.0). The mean duration of formal education was 6.7 years (SD 3.4, range 0-18) with no difference between women and men. The proportions of women, 246 (61%), and men, 157 (39%), are similar to those in the …