A prospective study of toddlers with ASD: short-term diagnostic and cognitive outcomes.

Background: Despite recent increases in the number of toddlers referred for a differential diagnosis of autism spectrum disorders (ASD), knowledge of short-term stability of the early diagnosis as well as cognitive outcomes in this cohort is still limited.
Method: Cognitive, social, and communication skills of 89 clinic-referred toddlers were assessed at the average age of 21.5 (SD = 4.9) months, and reassessed at 46.9 (SD = 7.7) months. Groups with stable and unstable diagnostic presentation were identified and compared on their profile of cognitive and social-communicative skills obtained at the time of initial diagnosis.
Results: Stability of the ASD diagnosis was 100%; diagnosis of autism was stable in 74% of cases as compared to 83% and 81% in PDD-NOS and Non-ASD groups, respectively. Worsening of social disability symptoms resulting in autism diagnosis was noted in 17% of toddlers initially diagnosed with PDD-NOS and in 19% of toddlers with initial diagnosis of non-ASD disorder. However, marked improvement was noted in approximately 1/4 of children initially presenting with autism, warranting diagnostic reassignment to PDD-NOS at follow-up. An analysis of developmental skills profiles suggests particular relevance of the assessment of verbal and nonverbal communication skills to diagnostic differentiation between subtypes within ASD in the second year of life.
Conclusions: Stability of ASD diagnosis in toddlers is high, though marked changes in severity of symptoms is to be expected in a minority of cases. Simultaneous consideration of cognitive, social, and communication skills profiles enhances accuracy of diagnostic classification and prediction of outcome.