Subclinical cognitive impairment: epidemiology and clinical characteristics.

Subclinical cognitive impairment is commonly reported in elderly populations, but its clinical significance is largely undetermined. It is commonly perceived as a normal feature of the aging process or a separate nosological entity. The clinical status of this disorder is explored herein by reference to longitudinal observations. It is concluded that persons with subclinical cognitive impairment constitute a highly heterogeneous group. There is an elevated risk in this group for senile dementia, with an estimated 18% incidence rate over 3 years, but in the majority of cases, this problem is more commonly associated with depressive symptomatology and physical illness. Only 13% of persons with recent observable change in cognitive functioning appear to have a totally benign and transient syndrome. Caution should be exercised in applying single unifying nosological entities such as age-associated memory impairment to this group of the elderly.