Transition from schizotypal disorder to non-affective psychotic disorders including schizophrenia: A nationwide Swedish cohort study.

This study evaluated the transition rates from schizotypal disorder to non-affective psychosis and schizophrenia in particular aiming to identify clinical and demographic factors associated with these transitions. We conducted a nationwide cohort study using data from the Swedish Patient Register and the Cause of Death Register, including patients aged 18 and older diagnosed with schizotypal disorder (ICD-10 F21) between 2006 and 2017. Cox proportional hazards regression was employed to assess the associations between baseline characteristics and transitions to schizophrenia (ICD-10 F20) and other non-affective psychotic disorders (ICD-10 F20-F29, excluding F21), with follow-up extending up to 12 years. Of the 667 patients included, 12.0 % transitioned to schizophrenia, and 22.5 % to other non-affective psychotic disorders. The estimated 10-year cumulative risks of transition were 24.6 % for schizophrenia and 43.5 % for non-affective psychotic disorders. Older age and diagnosis allocated during the study's early observation years were associated with a reduced risk of transition to schizophrenia, while pre-existing depression and anxiety disorders had protective effects. In contrast, substance use disorders other than alcohol were associated with an increased risk of transitioning to non-affective psychotic disorders. These findings highlight that a significant portion of individuals with schizotypal disorder progress to more severe psychotic disorders, underlining the need for careful monitoring, especially in those with comorbid substance use.