DR. BLACK: Do you believe there is a need to revamp or revise the DSM-IV PD criteria?
DR. ZIMMERMAN: I think a number of the arguments put forth by the DSM-5 Work Group as justifications for revising the criteria do not hold up to empirical study.
One of the issues is the argument that there’s too much comorbidity among PDs. The theory is that disorders are not unique diagnostic entities if they are so frequently comorbid with other disorders. But how much comorbidity is too much? The DSM-5 Work Group doesn’t say. Oldham et al4 found comorbidity rates of 70% to 90%, depending on which semi-structured diagnostic interview was used; however, this was among individuals presenting for psychodynamic treatment of PDs.
I wanted to look at the comorbidity rates in nontreatment-seeking samples to find out if treatment seeking is associated with comorbidity. I reviewed the literature and identified 7 general population epidemiological studies that presented data on the number of individuals with ≥2 PD diagnoses. In these studies, the comorbidity rate is approximately 25%, which is one-half or less than the rates found in patient populations.5 This finding suggested to me that this may not be a nosology problem unless you think 25% comorbidity is too high. The DSM-5 people don’t speak to that, although quite frankly with 10 PDs I don’t think the 25% comorbidity rate is excessive. However, a comorbidity rate of 25% was much lower than that found in patient samples and suggests to me that one of the primary stated reasons of deleting 4 PDs may not be valid.
DR. BLACK: Assuming there is a need to revise the PD section, how would you have gone about that process?
DR. ZIMMERMAN: Whatever deficiencies you perceive in the criteria, the process should be that you come up with an alternative, examine the alternative empirically, and this is followed by independent replication that the new approach is superior to the prior one. My view is that it is not sufficient justification to make a change because there is a problem with the prior approach.
We can argue as to whether there really are problems with, for example, the categorical nature of classification. My research group and I wrote a paper arguing that DSM-IV can be interpreted as having a dimensional component (Box).6 DSM-IV suggests that clinicians record on axis II that a patient has some traits of a disorder even when the full criteria are not met. With that in mind, we conceptualized DSM-IV as having a 3-point dimension, where 0 means no traits of the disorder, 1 indicates subthreshold traits, and 2 indicates that the disorder is present. In a study of >2,000 patients, we found that DSM-IV’s 3-point dimensional approach was as highly associated with measures of psychosocial morbidity as more finely graded dimensional systems.6 We therefore concluded that DSM-IV already includes a dimensional system and questioned why we need to change that approach.
Does DSM-IV already have a dimensional component?
Zimmerman et al suggested that DSM-IV personality disorder (PD) criteria can be thought of as a dimensional system.6 They evaluated 2,150 psychiatric outpatients using semi-structured diagnostic interviews and computed dimensional PD scores in 3 ways:
- 3-point dimension, where 0 means no traits of the disorder, 1 indicates subthreshold traits, and 2 indicates that the disorder is present
- number of DSM-IV criteria met
- 5-point dimension analogous to what was being proposed for DSM-5.
Patients also were evaluated for the presence of a PD based on DSM-IV diagnostic threshold. They then correlated these assessment methods with 7 indices of psychosocial morbidity—the number of current axis I disorders, Global Assessment of Functioning scores, unemployment in the past 5 years, number of psychiatric hospitalizations, level of psychosocial functioning, suicidal ideation at the time of the evaluation, and number of lifetime suicide attempts. All methods of dimensional assessment were more highly correlated with psychosocial morbidity than categorical classification and there was no difference among the 3 dimensional methods.
One of my concerns with the dimensional system as currently proposed is the uncertain significance and possible implications of someone being given a low, non-zero rating. How might this play out in a custody evaluation of someone who is said to be “a little borderline”? What might the implications of non-zero ratings be in obtaining life insurance? The potential practical consequences of low ratings have not, to my knowledge, been discussed. Because of this concern we decided to do a study to determine if there was any clinical significance to low dimensional scores. I had hypothesized that if we compared individuals who had no criteria and only 1 BPD criterion, there would be no difference.