by Michael D. Anestis, M.S.
When patients present at psychology clinics, the norm is for them to meet diagnostic criteria for more than one mental illness. This occurrence - simultaneously meeting diagnostic criteria for more than one mental illness - is known as comorbidity and has been shown in a number of studies to predict a more severe course. That being said, not all patterns of comorbidity were created equal, as some combinations have proven to be more problematic than others. Taking that a step further, it is not always clear that the symptoms of all of the comorbid conditions will increase in severity. In other words, the presence of comorbid conditions might make some conditions worse while not having much, if any, impact on others.
Today, I want to discuss a study recently published in Personality Disorders: Theory, Research, and Treatment by colleages at the University of Mississippi Medical Center - Han-Joo Lee, Courtney Bagge, Julie Schumacher, and Scott Coffey. In this study, the authors wanted to examine whether the precense of a current diagnosis of substance dependence impacted the severity of borderline personality disoder (BPD) symptoms. The authors noted that prior research has demonstrated that BPD predicts worse outcomes for substance users, including more severe drug use, greater likelihood of a suicide attempts, poorer overall psychological health, greater needle sharing, and poorer substance use disorder (SUD) treatment outcomes (e.g., Kruedelbach, McCormick, Schulz, & Grueneich, 1993; Nace, Saxon, & Shore, 1986). At the same time, they noted that very little research has examined whether the opposite pattern - SUDs negatively impacting BPD - holds true (for exceptions, see Links et al. 1995; Zanarini et al., 2004).
To examine this question, the authors examined data from 104 female participants, 34 of whom met criteria for BPD, but not substance dependence, 19 of whom met criteria for both BPD and substance dependence, and 48 who had never met criteria for either disorder. Of the individuals who met criteria for substance dependence, 58% were dependent upon one drug and 42% were dependent upon two drugs. The drugs most frequently endorsed as being used by these individuals were cocaine/crack (42.1%), alcohol (36.8%), sedatives (21.1%), opiates (21.1%), marijuana (5.3%), ampetamines (5.3%), and PCP (5.3%).
The authors determined diagnoses by administering semi-structured diagnostic interviews and also administered a series of questionnaires. Based upon theoretical reasons as well as significant correlations with the dependent variables in this study, past history of mood disorders, anxiety disorders, and antisocial personality disoder (ASPD) were included as covariates. What this means is that, when the authors examined whether individuals with SUD and BPD demonstrated worse BPD symptoms than individuals who met criteria for BPD but not an SUD, they wanted to ensure that any differences were not better accounted for by the precense of other forms of psychopathology throughout participants' lives.
In their main analyses, the authors compared participants on a number of variables, including:
- Overall BPD features
- Affective lability (rapidly shifting emotional states)
- Affective intensity and reaction
- Self-harming and suicidal tendencies
- Externalizing behaviors (physical fights, planned crime, unplanned crime, risky sexual behavior)
What they found was that, although the control group differed from both BPD groups on nearly all of these outcomes (affective intensity was the exception), the two BPD groups did not differ from one another on any of the six outcomes once they accounted for participants' history of mood and anxiety disorders and ASPD. These results also held true when the authors re-ran their analyses looking at lifetime diagnoses of substance dependence rather than only current diagnoses.
So what does this mean? Based on these data - and remember, they represent only one study - it does not appear that meeting diagnostic criteria for substance dependence negatively impacts the symptoms of BPD. This does not mean that SUDs are not important - it simply means that the two issues (BPD and SUD) are both problems, but that SUDs are not making BPD worse.
The next question is "why would BPD lead to worse SUD outcomes while the reverse is not true?" One interpretation could be that the underlying personality characteristics that drive BPD, things like impulsivity, rapidly shifting emotions, difficulty tolerating distress, and difficulties regulating emotions, make an individual vulnerable to a variety of maladaptive behaviors, but that maladaptive behaviors are unlikely to impact an individual's personality. What do you make of these findings?
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