An overview of the challenges with the differential diagnosis of schizotypal personality disorder

Schizotypal personality disorder (SPD) has a long history and there is still considerable ongoing research. Although there are overlapping features of SPD and other personality disorders, the full constellation of schizotypal features is broader. The longitudinal course of SPD is variable, with differences in trajectory manifesting lifelong clinical significance. Particularly important is the relationship between SPD and prodromal states that may result in an eventual diagnosis of psychosis. This review covers the history and differential diagnosis of SPD, including the older conceptualization of 'borderline schizophrenia.' Clinical, cognitive, functional, brain imaging, and genetic features of SPD, and the implications of age at onset and method of ascertainment of the condition are reviewed. Differences between psychometrically identified schizotypy, clinically diagnosed SPD, and other psychiatric conditions are described. A comprehensive literature search using MEDLINE (via PubMed) did not specify a date range, to capture the full scope of research. SPD is unique in that the age at ascertainment is critical for the persistence of the diagnosis. When diagnosed with SPD in late adolescence, some individuals develop psychosis, some remit, and others have persistent, lifelong symptoms. Predictors of conversion to psychosis have been identified but are no proven treatments.