Abstract
Psychotic disorders have varied clinical presentations, diagnostic stability is poor and other mental disorders often co-occur with the conditions. To improve the clinical and pathophysiological utility of classification systems for psychosis, it is necessary to consider how symptoms may reflect dimensions of psychopathology that extend beyond the boundaries of traditional diagnostic classifications. We examined personality deviation as a means for explaining symptom variation across individuals with serious mental illness. Participants (N = 312) with psychosis, first-degree biological relatives and healthy controls underwent comprehensive clinical evaluations that included symptom ratings and Diagnostic Statistical Manual consensus diagnoses. They completed the Personality Inventory for Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (PID-5), which provides multidimensional assessment of personality disturbances and characterizes psychosis-relevant phenomena, and the Schizotypal Personality Questionnaire (SPQ), a widely accepted measure of schizotypal traits. PID-5 was comparable with SPQ in differentiating between participants with and without psychosis. Greater psychotic symptomatology and higher scores on the SPQ Cognitive-perceptual dimension were associated with higher scores on PID-5 Psychoticism. Facet-level traits showed diverse associations with existing clinical syndromes, suggesting they have utility for quantifying separable symptom dimensions that cut across existing disorders. Yet the patient groups were similar across four of the five PID-5 personality trait domains, indicating shared patterns of personality expression that challenge existing categorical delineations. © 2019 John Wiley & Sons, Ltd.