Assessing premorbid cognitive ability in adults with type 2 diabetes mellitus--a review with implications for future intervention studies.

Associations between type 2 diabetes mellitus (T2DM) and accelerated cognitive decline are well established. However, the sensitivity of neuropsychological tests to detect early deficits in cognitively normal adults with T2DM is unknown. This review examined cognitive domains and specific neuropsychological tests that are impaired in T2DM, based on clinically significant differences (effect sizes >0.5) between T2DM and groups without T2DM. Nine cross-sectional studies were identified which reported means and standard deviations for individual tests. Tests of executive function, working memory and psychomotor and attentional functions were found to be impaired in T2DM. Impairments of executive function and choice reaction time may have consequences for everyday functioning, in particular the risk of falls in older adults. More research on cognitive deficits in dual-task situations and how they impact everyday functioning is needed; the Trail Making Task, Symbol Digit Modalities Test, Verbal Fluency Task and tests of reaction time and processing speed could be included as core components of test batteries in future intervention studies. They could also be assessed in newly diagnosed T2DM and used to monitor progressive deterioration of cognitive function and the efficacy of therapeutic interventions on cognitive function.