Positive and Negative Symptomology in ASD and Schizophrenia
Few studies have directly compared clinical dimensions of ASD and schizophrenia, and diagnostic confusion between these disorders persists. This study empirically investigated Foss-Feig et al.’s (2016) proposed framework to compare adults with ASD and schizophrenia in terms of positivesymptoms(the presence of atypical characteristics such as delusions, hallucinations, or restricted and repetitive behaviors), and negative symptoms (the absence or reduction of typical characteristics such as social initiation or affective sharing).
To identify shared and distinct symptomology between ASD and schizophrenia.
Participants were adults aged 18-35 who met DSM-5 criteria for ASD (n=59) or schizophrenia (n=45) and a group of typically developing (TD) controls (n=55). Participants completed the Scale for the Assessment of Positive Symptoms (SAPS) and Scale for the Assessment of Negative Symptoms (SANS) to assess schizophrenic symptoms, and the Autism Diagnostic Observation Schedule-2 (ADOS) to assess autism symptoms. ADOS items were designated as “positive” or “negative” following the framework developed by Foss-Feig et al. (2016). Items that could not be differentiated as positive or negative were not included in relevant analyses.
Across ASD, Schizophrenia and TD samples, the sensitivity of the ADOS was 71.2% and the specificity was 78.0%. Notably, 20 out of 45 participants with schizophrenia met ADOS criteria (44.4%). To understand symptomatology across disorders, we compared diagnostic groups on positive and negative symptomology. The main effect of diagnosis on positive ADOS symptoms was significant (F(2,80.23)=22.45, p<.001), and post hoc tests revealed that the ASD group scored higher on positive ADOS symptomology than both the SCZ and TD groups (ps<.001). For negative ADOS symptoms, the main effect of diagnosis was significant (F(2,93.21)=24.92, p<.001). Post hoc tests revealed that both the ASD and schizophrenia groups scored higher than the TD group on negative ADOS symptomology (ps<.005). There were not significant group differences between the ASD and schizophrenia groups (p=.097).
The main of effect of diagnosis on SAPS scores was significant (F(2,57.66)=17.59, p<.001). Post hoc tests revealed that the schizophrenia group had higher SAPS scores than both the ASD (p= .017) and TD groups (p<.001). The main effect of diagnosis on SANS scores was significant, (F(2,58.63)=67.96, p<.001). While both the ASD and schizophrenia group had higher SANS scores than the TD group (ps<.001), there were not significant group differences between the ASD and schizophrenia group (p=.571).
A pattern emerged such that both ASD and schizophrenia appear to share symptomology related to negative social symptoms, such as reduced social-emotional reciprocity (e.g., blunted affect, apathy, reduced affective sharing and reduced social overture and response). In contrast, positive symptomology qualitatively differentiated ASD and schizophrenia. Those with schizophrenia demonstrated higher positive symptoms related to psychosis (e.g., delusions and hallucinations) whereas those with ASD demonstrate higher positive symptoms associated with abnormalities in language and speech, restricted interests, and repetitive behaviors. The distinction between positive and negative symptoms may be useful for parsing heterogeneity within the ASD population and across disorders. However, there is a need to design measures of autism symptomology that clearly differentiate positive and negative symptoms.