Attention deficit hyperactivity disorder in adults : neuropsychological deficits and functional impairments

Abstract

The overall aim of the present thesis was to investigate the role of neuropsychological deficits in adult ADHD. Study I examined the psychometric properties of a new rating instrument, the Adult Executive Functioning Inventory (ADEXI), which focuses on deficits in working memory and inhibition. The internal consistency was high; the test-rest reliability was adequate, whereas the inter-rater reliability was low. The ADEXI correlated significantly with another executive functioning (EF) rating instrument. Few significant relations were found between the ADEXI and neuropsychological test scores. Adults with ADHD reported significantly higher deficits with regard to inhibition and working memory compared to both a clinical and a non-clinical control group.

Study II investigated how well neuropsychological measures can discriminate between adults with ADHD and adults with other psychiatric disorders. Adults with ADHD performed more poorly compared to clinical controls with regard to verbal memory, inhibition, set shifting, fluency, and delay aversion. The results remained significant when controlling for IQ, but only the effects of delay-aversion, fluency, and inhibition remained significant when controlling for basic cognitive functions. Sensitivity and specificity were adequate.

Study III investigated executive deficits and functional impairments in adults with ADHD and adults with other psychiatric disorders. ADHD subgroups with or without executive deficits were compared. Adults with ADHD had greater problems with academic, social, and daily life functioning, as well as with criminality. Adults with ADHD were also more often on sickness benefit, but less often unemployed compared to the clinical control group. The ADHD subgroup with executive deficits had poorer academic functioning, a higher proportion of individuals not working or on sickness benefits, and a higher rate of criminality.

Study IV investigated neuropsychological deficits (working memory, inhibition, planning, switching, fluency, speed of processing, and delay-related behaviors) in older adults with ADHD in comparison with both younger adults with ADHD and healthy older controls. Both variable- and person-oriented analyses were included. Older adults with ADHD differed from healthy controls with regard to working memory, inhibition, speed of processing, and delay-related behaviors. Older adults performed at a similar level with regard to working memory and verbal fluency, but significantly better with regard to inhibition and switching compared to younger adults with ADHD. Twenty percent (20%) of older adults with ADHD did not show a clear deficit in any neuropsychological domain.

In summary, adults with ADHD perform more poorly on neuropsychological tests compared to adults with other psychiatric disorders. There is a link between executive deficits and functional impairments, especially academic/occupational and social functioning. In line with current models of heterogeneity in ADHD, the present thesis has been able to demonstrate that only a subgroup of younger and older adults with ADHD have executive deficits.