Formal Thought Disorder in Children with Autism Spectrum Disorder: Indicator of Future Psychotic Symptoms or Indicator of Severe Autistic Symptoms. A Seven Year Follow up Study

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 to be the hallmark of psychotic disorders, but nowadays it is considered as an important symptom of autism spectrum disorders (ASD) as well. FTD in childhood might be a developmental precursor of psychotic disorders or a manifestation of more severe impairment in ASD.

Objectives:  The current longitudinal study is a seven year follow-up on 91 individuals with ASD, and it was investigated 1) whether symptoms of FTD during childhood predicted prodromal symptoms of psychosis in adolescence, and 2) whether symptoms of FTD during childhood were associated with higher ASD symptom severity in adolescence.

Methods:  ASD symptom severity was assessed in childhood (T1) and seven years later in adolescence (T2), using the Autism Diagnostic Observation Schedule (ADOS). At T1, the Kiddie-Formal Thought Disorder Scale (KFTDS) was used to measure symptoms of FTD. At T2, the Prodromal Questionnaire (PQ) was used to assess (pre)psychotic symptoms.

Results:  FTD symptoms at T1 did not predict prodromal symptoms of psychosis at T2. FTD symptoms at T1, especially loose associations predicted severity of autism spectrum disorder at T2 over a period of 7 years.

Conclusions:  FTD predicts more severe symptoms of ASD over a period of seven years and appears to be a manifestation of more severe impairment in ASD, but does not predict prodromal symptoms of psychosis.