Persistence of autistic symptom differences by severity among individuals at clinical high risk for psychosis and with first-episode psychosis: An 18-month longitudinal follow-up study

Autistic symptoms influence functional outcomes in individuals at high clinical risk for psychosis (CHR-P) and in those with first-episode psychosis (FEP). Our recent findings suggest that these symptoms encompass both enduring trait-like and transient state-like features that improve with treatment over a 12-month period. This study aimed to clarify the long-term course of autistic and non-autistic symptoms by comparing individuals with high and low levels of autistic symptoms at the CHR-P and FEP over an extended 18-month period. Sixty-two participants who completed the 18-month follow-up assessment (CHR-P, n = 37; FEP, n = 25) were included. At baseline, the high autistic symptoms (HA) group exhibited a significantly greater severity of autistic symptoms, more severe non-autistic psychiatric symptoms, and lower global functioning than the low autistic symptoms (LA) group. Over the 12- and 18-month follow-up periods, both groups showed significant improvements in non-autistic psychiatric symptoms and global functioning, and the initial group differences in these domains were no longer statistically significant. In contrast, although the autistic symptoms in the HA group decreased over time, a significant difference in the PAUSS total scores between the HA and LA groups persisted throughout the follow-up. While non-autistic psychiatric symptoms and functional impairments are responsive to treatment, autistic symptoms in individuals with CHR-P and FEP may encompass both modifiable, state-like features, and stable, trait-like characteristics, persisting over an 18-month period. Further research is warranted to elucidate the underlying mechanisms and clinical implications of persistent autistic symptoms in early psychosis. • Autistic symptoms were assessed using the PAUSS in individuals with CHR-P and FEP. • Participants with CHR-P and FEP were grouped by baseline autistic symptom levels. • High autistic group in the CHR-P/FEP showed significant improvement over 18 months. • The differences of autistic symptoms among the two groups persisted at 12 and 18 months. • Autistic symptoms in CHR-P/FEP may reflect both state- and trait-like features.