Formal Thought Disorder in Children with ASD: Prevalence, Relations with Communication Impairment and Prediction of (pre)Psychotic Symptoms During Adolescence

Background: Formal Thought Disorder (FTD) is a disruption in the flow of thought, which is inferred from the disorganization of spoken language and which is a manifestation of severely disturbed language processing. FTD was once considered as the hallmark of schizophrenia, but nowadays it is considered as an important symptom of autism spectrum disorders (ASD) as well. FTD can be a neurodevelopmental precursor of schizophrenia or it can be mainly a manifestation of severe communication impairment in ASD.

Objectives: The current study investigated in a longitudinal study of 142 individuals with ASD 1) the prevalence of FTD in childhood, 2) the relation between FTD and communication impairment in childhood, and 3) whether signs of formal thought disorder (FTD) during childhood predicted a prodromal state of psychosis during adolescence.

Methods: Overall ASD severity and more specifically communication impairment was assessed during childhood (T1) and adolescence (T2) using the Autism Diagnostic Observation Schedule (ADOS). At T1, the Kiddie-Formal Thought Disorder Scale (KFTDS) was used to systematically measure FTD. At T2, the Thought Problems Scale of the Child Behavior Checklist (CBCL), the Prodromal Questionnaire (PQ) and the Composite Assessment of At Risk Mental Symptoms (CAARMS) were used to assess (pre)psychotic symptoms. The prevalence of FTD was investigated by identifying the children that scored above the KFTDS threshold within the T1 ASD group (n=142). Children that scored above this threshold were compared with the children that scored below the threshold on the T1 ADOS communication impairment subdomain, and they were compared on PQ and CAARMS scores at T2.

Results: During childhood, 69% (n=98) of our ASD sample had a FTD according to the KFTDS threshold. Children that scored above this threshold had significantly higher ADOS communication impairment scores at T1 than those who scored below the KFTDS threshold (p=.04). At T2, individuals with FTD at T1 scored higher on the Thought Problems Scale of the CBCL (p=.05), but not on the PQ or CAARMS.

Conclusions: FTD is very prevalent among children with ASD. FTD seems to be a manifestation of severe communication impairment in ASD and not so much a precursor of psychosis.