IDENTIFYING AUTISM Spectrum DISORDERS (ASD) In A MIXED POPULATION of Adults with ASD or ADHD Woth the AQ and the Temperament and Character INVENTORY Personality Questionnaire

Background:  Diagnosing ASD and ADHD in adults is hampered by the lack of reliable developmental information, and the heterogenic phenotypes with overlapping symptoms. In adults, both ASD and ADHD present with symptoms that could also be attributed to personality pathology on account of affective, cognitive and interpersonal problems. In other words, we could also consider differences between both developmental disorders from the perspective of personality pathology. Given the diagnostic ambiguity between ASD and ADHD in clinical practice, it is important to determine the extent to which the personality perspective can differentiate between ASD and ADHD.

Objectives:  To investigate whether ASD can be identified more effectively in a mixed population of adults with ASD or ADHD using a personality instrument rather than an ASD-specific instrument.  More specifically we examine (a) the association between the autism spectrum quotient (AQ) subscales and the abbreviated temperament and character inventory (VTCI ) subscales, (b) which instrument is the best predictor of ASD in this mixed population, and (c) whether the VTCI adds to the predictive value of the AQ in the identification of ASD and vice versa.

Methods:   54 adults with ASD and 21 with ADHD all without a (history of) substance use disorder completed the AQ (50 items) and the VTCI (105 items). The relationship between the VTCI and the AQ was examined using a principal component analysis pooling the 7 VTCI subscales and the 5 AQ subscales. We computed the percentage correctly identified ASD cases in the mixed sample with binominal logistic regression analysis.

Results:   The ASD and ADHD groups were comparable with respect to age and IQ, but male patients were overrepresented in the ASD group (X²=5.812, p=.016). ASD and ADHD patients differ significantly and on 3 of the 5 AQ subscales as well as on 4 of the 7 VTCI scales. There were significant and substantial correlations between the AQ total score and the AQ social skill subscale and most of the VTCI scales, with the exception of persistence. Furthermore, the principal component analysis with all scales of both instruments showed that the subscales of both instruments were complimentary to each other in the first three of the five factors that were extracted. Furthermore, our results showed that the autism-specific instrument (AQ) is not superior to the personality instrument (VTCI) in differentiating between ASD and ADHD.  In fact both instruments yield the same improvement in correctly diagnosing ASD and ADHD compared to pure chance: from 75% to 86.7% correctly identified cases.

Conclusions:   This current study suggests that in a mixed sample of adults with ADHD or ASD, autistic features as measured by the AQ are highly correlated to personality characteristics as measured by the VTCI. Both instruments differentiate ASD from ADHD in this mixed sample with the same accuracy. More research is needed to understand the relationship between developmental disorders and personality characteristics.