Prevalence and construct validity of Personality Disorder Not Otherwise Specified (PDNOS).

Personality Disorder Not Otherwise Specified (PDNOS) is one of the most frequently used Axis II diagnoses, yet explicit guidelines for its assessment are lacking. To investigate the prevalence and construct validity of various definitions of PDNOS, 1760 psychotherapy referrals were diagnosed using the Structured Interview for DSM-IV Personality Disorders (SIDP-IV). Construct validity parameters included severity of psychiatric complaints, personality symptoms, and functional impairment. Results show that PDNOS is highly prevalent in this sample (21.6% or 70.8%, depending on whether co-occurrence with formal PD is allowed). Patients with both formal PD and PDNOS have more severe problems than those with formal PD only. In terms of severity, PDNOS takes an intermediate position between formal and no PD. For mixed PD, a cut-off of 5 criteria would yield a large (12.0%) additional PD group with a similar level of functional impairment as compared to mixed PD with a cut-off of either 10 or 15 criteria. In conclusion, the high prevalence of PDNOS warrants proportional attention in science and practice. If PDNOS is retained in DSM-V, it is recommendable to develop explicit guidelines for its assessment.