The validity of two diagnostic systems for personality disorder in people with intellectual disabilities: a short report

Over the last ten years, there has been greater interest in the diagnosis of personality disorder (PD) in people with intellectual and developmental disabilities (IDD). One important characteristic of a diagnostic system is that it should have validity as a contribution to utility. PD has been found to have a predictive relationship with violence and the purpose of this paper is to review two methods for the diagnosis of PD in offenders with IDD in order to evaluate the utility of the diagnoses.

In total, 212 offenders with ID were recruited from three settings – maximum-security, medium/low security and community services. Diagnoses of PD in the case files were compared with a structured system of diagnosis based on DSM-IV traits.

There were significant differences between the two systems with a significantly higher frequency of PD diagnosis in the community forensic setting in the structured assessment system. There was no relationship between the case files diagnosis of PD and future violence but there was a significant predictive relationship between the structured diagnosis of PD and future violence with an AUC=0.62.

As with all such studies, the research is limited by the quality of the case files available to the researchers.

Only the structured assessment of PD had utility for the prediction of violence. Reasons for the differences between the systems are discussed and suggestions made on how a diagnosis of PD can be structured for the busy clinician.

The accurate diagnosis of PD has important implications since the PD is a crucial addition to any violence risk evaluation.

This study is the first of its kind to review the way in which clinicians assess PD.