Change In ADOS Classification In An Inception Cohort of Preschool Children with ASD

Background:  The Autism Diagnostic Observation Schedule (ADOS; Lord et al. 2000) assesses communication, social and play skills, and restrictive/repetitive behaviours.  Gotham et al. (2007, 2009) revised the ADOS algorithms for modules 1 to 3 to improve diagnostic validity, and developed a calibrated metric as an index of ASD symptom severity.  The revised algorithms and severity metric allow for comparison across modules, age and time.

Objectives:  To investigate change in ADOS classification in a sample of preschool children with ASD participating in a Canadian longitudinal study and to identify factors that may be associated with this change.

Methods:  The sample consisted of 191 children assessed with the ADOS at enrolment (within 4 months of diagnosis) between ages 2 and 4 (Time 1; T1) and when they were 6 (Time 2; T2). Within this sample, 147 children (77%) were in the ADOS autism category at T1 and T2 (AA group); 8 (4%) went from an autism diagnosis at T1 to ASD at T2, and 19 (10%) went from autism at T1 to non-ASD at T2 (AN group). For the 17 (9%) children with ASD at T1, 12 moved to autism at T2, 2 remained ASD at both T1 and T2, and 3 shifted to non-ASD at T2. The analyses focused on the AA and AN groups as they had the largest sample sizes and the AN group showed greatest diagnostic change.  Comparisons were made between the two groups on selected baseline variables. Change between T1 and T2 was assessed using Multivariate Analysis of Variance (MANOVA) for baseline variables showing a medium-to-large effect size (ES≥.5) while controlling for age and gender.

Results:  No significant AA versus AN differences were found in the children’s ages (2, 3 or 4) at T1 (p=.94).  More boys were in the AA group (87%) than in the AN group (68%, p=.03). Variables significantly different at baseline or showing at least a medium effect size included the Merrill Palmer-Revised (MP-R) developmental index growth score (p=.05, ES=.5), PLS-4 total language SS (p=.007, ES=.7), VABS-II communication SS (p=.056, ES=.5) and ADI-R social domain total score (p=.002, ES=.7).  Similar or larger effect sizes were observed at T2 on these variables.  MANOVA results indicated parallel paths between the groups for MP-R, PLS-4 and ADI social scores.  A trend towards divergent paths was found on the VABS communication score with the AN group having a steeper slope.

Conclusions:  These preliminary results revealed that 10% of the children with ASD changed from an ADOS autism diagnosis at T1 (diagnosis/enrolment) to non-ASD at T2, 2-4 years later (age 6). This change could be due to misclassification, or variation in baseline characteristics, or level of services received.  In addition, a greater improvement in functional use of communication as reported by the parents for the AN group is seen relative to the AA group.  Further research is necessary to understand why these children moved from autism to non-ASD, and to examine the implications of VABS communication scores in relation to change in ADOS classification.