Overlap between borderline and schizotypal personality disorders

Borderline personality was split into two diagnostic categories in DSM-III: borderline personality disorder (BPD) and schizotypal personality disorder (SPD). There remains a great deal of diagnostic overlap between these two categories despite modifications in DSM-III-R. This report discusses four possible hypotheses for this overlap: (1) an independent, random association; (2) artifactual overlap due to imperfections in the criteria sets; (3) a synergistic association of the two personality disorders; and (4) a manifestation of dimensional psychopathology. Empirical evidence for each of the first three hypotheses is weak and contradictory. Recent biologic and treatment studies appear to most strongly support the use of dimensional models of "borderline" and "schizotypal" personality traits.