Digit span and verbal fluency tests in patients with mild cognitive impairment and normal subjects in Thai-community

Far too little attention has been paid to the difference of Digit Span test and category verbal fluency test (CVFT) between normal and mild cognitive impairment (MCI) subjects.

To investigate the difference of Digit Span test and CVFT between normal subjects and patients with MCI and study the influence of age, gender, and education on the task performance.

The authors collected data of 77 participants diagnosed with amnestic MCI (from 517 participants screened) and 30 normal subjects aged 50 or over enrolled from communities in Bangkok. The Digit Span test and CVFT (semantic fluency and Controlled word association test for letter fluency) were used to evaluate the subjects.

MCI patients had significantly lower digit span score, in both Digits Forward and Digits Backward, poorer performance on semantic fluency for animals and fruits and letter fluency test. The logistic regression model of MCI diagnosis showed that only Digits Backward score was a predictor of MCI diagnosis (OR 0.643 for each increment of 1 digit, p = 0.009, 95% confidence interval 0.462-0.896). The cut-off point of Digit Backward score was 4 and yielded sensitivity of 77% and specificity of 57%. Females had lower scores than males in every test except semantic fluency for fruits. The digit span and semantic fluency scores decreased as age increased but letter fluency increased correspondently with age. The digit span and CVFT scores increased in parallel with the increase of education.

MCI patients had poorer performance on the Digit Span and CVFT tests than normal age and education matched subjects. Digits Backward test can predict the MCI diagnosis. Age, gender and education have an impact on the performance of the tests.