A crucial feature of PDs is that of impairment or dysfunction (Hill & Rutter, 1994
; Tyrer & Alexander, 1979
), and this study has importantly shown that PD severity, was strongly related to an independent measure of mental impairment. However, disability increased from no PD to subthreshold PD only for major depressive disorder, panic disorder with agoraphobia and specific phobia, findings that only partially support the distinction between no PD and subthreshold PD in this classification. Similarly, disability associated with simple PD was significantly greater than disability associated with subthreshold PD only among individuals with bipolar I disorder and panic disorder without agoraphobia again signaling even less support for the validity of the dimensional PD classification with regard to the subthreshold PD versus simple PD distinction. In contrast there was strong support for the complex PD versus other levels of PD distinction, since disability associated with complex PD, with few exceptions, was greater than that associated with simple, subthreshold and no PD. It is possible that planned replications of these findings using all 10 DSM-IV PDs assessed in the Wave 2 NESARC will find stronger support for the no PD versus subthreshold PD and subthreshold PD versus simple PD distinctions.
The disability results of this study mirror those of prospective study of patients with anxiety and mood disorders (Seivewright, Tyrer & Johnson, 2004
). In this study global outcome and social function at 12 year follow-up were indistinguishable between no PD and subthreshold PD, somewhat greater for simple PD versus no PD and subthreshold PD and substantially worse for complex PD versus other levels of PD severity. Taken together, these findings suggest collapsing the no PD and subthreshold PD levels of this severity classification. If this were done, one would expect to find significant increases in disability in the combined no PD-subthreshold PD level relative to the simple PD level, a result not observed in this study for any Axis I disorder except bipolar I disorder and panic disorder without agoraphobia. Substantial increases in disability were also associated with complex PD compared with all less severe levels of this classification highlighting the important contribution of diffuse personality psychopathology to disability among individuals with Axis I disorders. Further research examining disability and these proposed new levels of PD severity for specific psychiatric disorders appears warranted.
One disparate finding in this study was that disability was not associated with level of PD severity among individuals with drug use disorders, a result not found for alcohol or nicotine dependence or any mood or anxiety disorder. This result suggests that disability associated with drug use disorders may be so great that incremental increases in disability due to increases in severity of PDs has little effect on impairment. Alternatively, the omission of narcissistic, borderline and schizotypal PD assessment may have contributed to the results, if these 3 PDs are highly comorbid with drug use disorders in the general population. Further research should address the important difference in observed disability with respect to PD severity among individuals with drug use disorders.
As Verheul (2005)
has emphasized, it is the clinical utility of any PD association that will carry the most weight in clinical practice. Although the present cross-sectional study found support for the utility of the dimensional classification proposed by Tyrer and associates with regard to the distinction between complex PD and simple PD and for a combined no PD-subthreshold PD level of severity, a stronger test of its clinical utility is best addressed prospectively. The Wave 2 NESARC, currently in the data preparation status, will importantly address this limitation of the present study by allowing for an examination of the impact of PD severity at baseline on disability at 3-to-4 year follow-up for a broad range of Axis I disorders. The NESARC samples are large enough to examine this relationship among individuals who have and those who have not received treatment over the follow-up period. If these associations are confirmed, and disability and impairment do not improve among those who received treatment, attention to the personality dysfunction might be considered to promote better long-term functioning among individuals with Axis I disorders. Planned Wave 2 NESARC analyses will also address another limitation of this study, that is, the exclusion of 3 DSM-IV PDs (narcissistic, schizotypal and borderline) not measured in the Wave 1 NESARC, allowing a more complete classification of PD severity.