Behavioural equivalents of schizophrenia in people with intellectual disability and autism spectrum disorder. A selective review.

Assessment of schizophrenia (SCZ) in people with autism spectrum disorder (ASD) is complicated due to confounding symptoms between ASD and SCZ. These confounding factors are aggravated when the patient has sparse verbal skills. A selective review was conducted to identify behavioural equivalents when assessing SCZ in individuals with ASD with sparse verbal skills, from 16 years of age. Only clinical papers were reviewed. Eight relevant articles were analysed for the use of behavioural equivalents in clinical settings. The results showed that especially disorganized speech and behaviour and negative symptoms can be observed in patients with SCZ and ASD who speak sparsely. It is not possible to observe delusions, but they may be reported by the patients when treated adequately for some time, usually months. Hallucinations cannot be observed directly, but 'hallucinatory behaviour' may be interpreted as hallucinations when observed concurrently with other SCZ symptoms. Additionally, age of onset and marked impaired global functioning compared to habitual functioning may constitute a diagnosis of SCZ in ASD. ASD is considered a lifelong condition and may be identified within the first 3-4 years, while SCZ onset is usually in adolescence or early adulthood. © The British Society of Developmental Disabilities 2021.