Diagnosing ASD in Adults: The Use of the ADOS Module 4

Background: Diagnosing Austism spectrum disorders (ASDs) in adults is complicated due to behavioral overlap with other disorders and limited access to developmental historical information. Standardized instruments may serve as tools to facilitate the diagnostic procedure in order to help the clinician judge on the presence of an ASD. The Autism Diagnostic Observation Schedule (ADOS) has a module for adults with fluent speech. After publication of the manual and the initial research underlying the validity and reliability of the ADOS module 4, there has been little research on the use of the ADOS in adults, while the need for instruments that assist the clinician’s diagnosis in adults has been growing. Therefore, more research on module 4 of the ADOS in an independent sample is valuable.

Objectives: The current study aims to investigate the psychometric qualities of the ADOS module 4 with respect to the classification and the domains.

Methods: The ADOS module 4 was administered to 93 males aged 18 through 66, in four groups based on clinical diagnosis: ASD (n=38), Psychopathy (n=16), Schizophrenia (n=18) and no clinical diagnosis (n=21). Groups did not differ with respect to age and IQ. The ADOS was administered and scored by trained and experienced examiners, who all had reached inter-rater reliability. Scoring was obtained from two different researchers and discrepancies between their scores were discussed to reach consensus.

Results: ANOVA’s showed significant main effects of group on the social and communication subdomains. Post-hoc tests showed that the group with ASD scored significantly higher compared to the Psychopathy group (p<0.005) and the Control group (p <0.001) on both domains. The group with Schizophrenia also scored significantly higher than the control group (p=0.05) on Communication and higher than the Psychopathy (p<0.05) and the Control group (p<.005) on the Social domain. Compared to the group with Schizophrenia, the group with ASD did not score higher on the Communication (p=.471) nor Social domain (p=.118). However, when comparing the participants with AD (n=8) with the group with Schizophrenia, the group with AD did obtain higher scores on the social domain (p=.026, Mann-Whitney U-test). Outcome on the ADOS for participants with Schizophrenia was related to their scores on the Positive and Negative Symptom Scale (PANNS): more negative symptomatology was associated with higher scores on the social domain (r=.586, p<.05) and total score (r=.553, p<.05).

Conclusions: The ADOS module 4 assists the clinician in differentiating ASDs from Psychopathy and from persons with no clinical diagnosis. Additionally, autism is distinguishable from Schizophrenia on the social domain. Difficulties in distinguishing ASDs from Schizophrenia seem to be related to the nature of both disorders and to the relatively high-functioning ASD group in this study.