Variability in performance: identifying early signs of future cognitive impairment.

OBJECTIVE: The current study examined whether year-to-year variability in cognitive performance differ between individuals cognitively unimpaired and individuals who subsequently develop dementia.
METHOD: Analyses included a case-control sample of Baltimore Longitudinal Study of Aging (BLSA; mean [M] age = 69.90, standard deviation [SD] = 8.92) participants. One hundred and 35 clinically diagnosed demented participants were matched with 135 nondemented participants based on age at initial testing and sex. Cognitive performance was examined using measures of memory, executive function, attention, language, and global mental status performance. Cognitive performance was examined from baseline to 5 years before cognitive impairment (M, assessments = 3.03, SD = 2.80).
RESULTS: As compared with unimpaired individuals, individuals diagnosed with dementia had greater variability on measures of attention, executive function, language, and semantic memory at least 5 years before the estimated onset of cognitive impairment, which may be indicative of maladaptive cognitive functioning. The dementia cases, however, had less variability on visual memory than the unimpaired group, which may suggest that these cases had more difficulty learning.
CONCLUSIONS: These results demonstrate that performance variability indexed over annual or biennial visits may be useful in identifying early signs of subsequent cognitive impairment.