Dr Michelle Garnett, Clinical Psychologist
Prevalence of Schizophrenia Spectrum Disorders in Average-IQ Adults with Autism Spectrum Disorders: A Meta-analysis
Lugo Marin, J et al. (2018). Journal of Autism and Developmental Disorders (2018), Vol. 48, pp 239-250
Since their separation as independent conditions, Autism Spectrum Disorders (ASD) and Schizophrenia Spectrum Disorders (SSD) can be misconceptualised as mutually exclusive disorders. Similarities between both disorders can lead to misdiagnosis, especially when it comes to average-IQ adults who were not identified during childhood. The aim of this meta-analysis was to examine the occurrence of SSD in average-IQ adults with ASD.
The pooled prevalence of SSD in the total ASD sample was close to 6%, pointing to a high co-occurrence of the two conditions.
The two diagnoses can be confused with great ease. First, the idiosyncratic beliefs of a person with ASD can be confused with the delusional ideas of a person with psychosis. Delusions do not follow logical reasoning, whereas in the person with ASD, rationality can be glimpsed within their speech. Also, the cognitive (and behavioural) inflexibility of people with ASD can be confused with the typically delusional conviction of psychosis.
Both conditions can coexist.
A significant contribution of this review is to describe symptoms similar to psychosis (psychosis-like symptoms) which would occur in a person with ASD as a result of unexpected stress factors.
They might develop delusional thoughts that would protect them from the subjective perception of lack of control. Furthermore, the authors found that these beliefs had a component of grandiosity or, in cases where there is a processing bias, a component of injury and/or threat. In clinical practice, Bakken and Hoidal (2014) reported the assessment of 12 cases set in a psychiatric unit for an adult population diagnosed with both ASD and schizophrenia. They concluded that those symptoms that best discriminated between the disorders, being more common is SSD, were:
• the presence of hallucinations
• disorganised speech and behaviour ,
• the occurrence of relapses in relation to psychotic symptoms.
Formal thought disorders (FTD) are very common in the ASD population. Solomon et al. (2008) found that executive control and anxiety were related to illogical thinking and loose associations, respectively.
The article usefully increases professional and community awareness that ASD and SSD can co-occur, but that there is a risk of misdiagnosis of a psychotic condition instead of ASD because of commonly occurring psychosis-like symptoms in ASD. The diagnostic assessment in this case needs to be conducted by a person with knowledge and skill in the assessment of both conditions.
(Please refer to the original article for further detail and the full references for the cited studies.)