Psychiatric Differential Diagnosis and Comorbidity In Children And Youth Referred For Assessment Of Possible ASD

Background: Children and youth (C&Y) with ASD have a higher risk for comorbid psychiatric disorders. Research has also found substantial symptom overlap between ASD and psychiatric disorders.  Previous reports have utilized standardized diagnostic procedures for either ASD or psychiatric disorders, but rarely both.

Objectives: To investigate the patterns of differential diagnosis and psychiatric co-morbidity in C&Y referred for assessment of possible ASD utilizing standardized ASD and psychiatric diagnostic measures.

Methods: C&Y referred to the British Columbia Autism Assessment Network (BCAAN) between 2002-2007 were included (n=580; age range=1-18; mean age=7.65). Subjects were assessed for both ASD and psychiatric disorder by an experienced child psychiatrist (utilizing ADI-R, ADOS, and DSM-IV psychiatric diagnostic assessment). Pediatric, psychological and communication assessments were available for most subjects. DSM-IV/TR multi-axial diagnoses were arrived at for each subject.

Results: 2/3 of C&Y referred were between 4 - 11 years old (33.1% <6 years; 66.9% >6 years). ASD was diagnosed in 196 (33.8%), and ASD was excluded in 384 (66.2%) subjects.  As a group, the most frequent comorbid syndromes were ADHD (59.1%), Anxiety Disorders (ANX) (45.4%), Mental Retardation (MR) (25.3%), and Tic Disorders (19.3%).  Between groups, children with ASD <6 years were more likely to have to have MR (43.8%), whereas non-ASD children < 6 years had a higher frequency of Communication Disorders (91.1%), ADHD (50.9%), and ANX (44.8%). Amongst C&Y > 6 years, non-ASD subjects had a higher frequency of ADHD (73.5%) and learning disorder (39.7%).  

Conclusions: C&Y referred for possible ASD have a high baseline rate and complex pattern of comorbidity that is relevant to both differential diagnosis and comprehensive functional formulation. In general, all younger children have less psychiatric comorbidity. In school-age subjects, non-ASD subjects appear to have a more complex comorbidity burden. Implications for assessment, service development, and research will be described.