Anxiety disorders are highly prevalent among individuals with borderline personality disorder, with comorbidity rates of up to 90%. Anxiety disorders have been found to reduce the likelihood of achieving remission from borderline personality disorder over time and to increase the risk of suicide and self-injury in this population. Evidence-based treatments for borderline personality disorder have not sufficiently focused on targeting anxiety disorders, and their effects on these disorders are either limited or unknown. Conversely, evidence-based treatments for anxiety disorders typically exclude suicidal, self-injuring, and seriously comorbid patients, thereby limiting their generalizability to individuals with borderline personality disorder. To address these limitations, recent research has begun to emerge focused on developing and evaluating treatments for individuals with co-occurring borderline personality disorder and anxiety disorders, specifically posttraumatic stress disorder (PTSD), with promising initial results. However, there is a need for additional research in this area, particularly studies evaluating the treatment of anxiety disorders among high-risk and complex borderline personality disorder patients.
Borderline personality disorder is a severe and complex psychological disorder characterized by long-term patterns of intense emotions, impulsive and self-destructive behaviors, and chaotic relationships. Borderline personality disorder is also associated with high rates of comorbidity. Individuals with borderline personality disorder meet criteria for an average of 3.0 to 3.4 current Axis I disorders (e.g. mood, anxiety, eating, psychotic, and substance use disorders) and 4.2 to 4.8 lifetime Axis I disorders [1,2]. Although emphasis is often placed on the comorbidity between borderline personality disorder and mood disorders, anxiety disorders are equally and highly prevalent, with approximately 75-90% of individuals with borderline personality disorder meeting criteria for at least one lifetime anxiety disorder [3–5]. Despite the negative prognostic significance of anxiety disorders on borderline personality disorder , there is a paucity of research examining effective treatments for these frequently co-occurring disorders, particularly among severe borderline personality disorder patients. The present review will describe the existing research in this area and make suggestions for future directions.
The prevalence, course, and impact of anxiety disorders in borderline personality disorder
Although the high rate of comorbidity between borderline personality disorder and PTSD has received the most theoretical and empirical attention, each of the anxiety disorders has been found to be prevalent among individuals with borderline personality disorder. Among borderline personality disorder inpatients, 88% meet criteria for a lifetime anxiety disorder, including PTSD (56%), panic disorder (48%), social anxiety disorder (46%), specific phobia (32%), obsessive compulsive disorder (16%), generalized anxiety disorder (14%), and agoraphobia (12%) . Similarly, high rates of current and lifetime anxiety disorders have been found among borderline personality disorder outpatients , treatment-seeking individuals with borderline personality disorder , and community samples of borderline personality disorder individuals . Anxiety disorders are more prevalent among borderline personality disorder patients than other clinical populations [1,4], and among women than men with borderline personality disorder [5,8]. Anxiety disorders also have a complex and variable course in borderline personality disorder, with high rates of remission (77-100%), recurrence (30-65%), and new onsets (15-45%) over 10 years of prospective follow-up [9,10]. Perhaps most critically, anxiety disorders are associated with a heightened risk of suicidal and non-suicidal self-injury among individuals with borderline personality disorder [11–18] and have been found to decrease the likelihood of achieving remission from borderline personality disorder over time .
The efficacy of borderline personality disorder treatments for co-occurring anxiety disorders
To date, there have been 14 randomized controlled trials (RCTs) that have examined the effects of borderline personality disorder treatments on anxiety, with all but one of these focused on general anxiety severity as opposed to specific anxiety disorder diagnoses (Table 1). The one study that has evaluated the effects of borderline personality disorder treatment on anxiety disorder diagnoses found that, among suicidal borderline personality disorder women in Dialectical Behavior Therapy, rates of remission from anxiety disorders ranged from 35-47% . These remission rates did not differ from those found in the Community Treatment by Experts control condition (24-54%), and were lower than those found for mood, substance, and eating disorders in Dialectical Behavior Therapy (64-88%) . The remaining 13 studies have examined general anxiety severity and have found mixed results. At post-treatment and/or follow-up, nine studies found significant decreases in anxiety [19–28], one study did not find a significant decrease , and three studies did not report pre-post changes [30–33]. Additionally, six studies found significant treatment differences in anxiety outcomes [19–22,26,27,33], whereas seven studies found no differences between treatments [23–25,28–32]. Although these studies generally indicate that treatment for borderline personality disorder is associated with a significant reduction in anxiety severity, it is unknown if or how these improvements are related to anxiety disorder diagnostic status. Of note, several borderline personality disorder treatments that have been examined in RCTs have not yet been evaluated in terms of their impact on anxiety outcomes, including Schema-Focused Therapy, Systems Training for Emotional Predictability and Problem Solving, Dynamic Deconstructive Psychotherapy, and General Psychiatric Management (see  for a review of these treatments).