The interactive role of distress tolerance and borderline personality disorder in suicide attempts among substance users in residential treatment

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Comprehensive Psychiatry 53 (2012) 1208 – 1216 www.elsevier.com/locate/comppsych

The interactive role of distress tolerance and borderline personality disorder in suicide attempts among substance users in residential treatment Michael D. Anestis a, b,⁎, Kim L. Gratz b , Courtney L. Bagge b , Matthew T. Tull b a

Military Suicide Research Consortium, Tallahassee, FL, USA University of Mississippi Medical Center, Jackson, MS, USA

b

Abstract The primary purpose of this study was to examine the interactive effect of borderline personality disorder (BPD) and distress tolerance (DT) on suicidal behavior across levels of intent to die (clear vs ambiguous) and medical severity. One hundred seventy-six adult patients in residential substance use disorder treatment were administered a series of structured interviews, behavioral assessments, and self-report questionnaires. A series of analyses of covariance and multiple regression analyses were conducted to test hypotheses using both categorical and dimensional measures of BPD and DT. Analyses supported hypotheses, indicating that patients with BPD who exhibit high DT are at the greatest risk for engaging in chronic and medically serious suicidal behavior. Although high DT is unlikely to be inherently problematic, results suggest that within the context of severe psychopathology (eg, co-occurring BPD–substance use disorder), the ability to withstand aversive internal states in pursuit of a goal (eg, one's own death) may enable individuals to persist in otherwise unsustainable behavior. In this sense, DT may function in a manner consistent with the acquired capability for suicide (a component of the interpersonal-psychological theory of suicidal behavior defined by a diminished fear of death and enhanced tolerance for pain that, in the presence of suicidal desire, enables individuals to enact lethal self-injury). © 2012 Elsevier Inc. All rights reserved.

1. Introduction Suicide claims the lives of approximately 34,000 Americans annually [1]. Research has revealed a wide range of risk factors for suicidal behavior, including hopelessness, depression, substance use, and non-suicidal deliberate self-harm [2-4]. Certain clinical populations have also been found to be at increased risk for suicidal behaviors, most notably individuals with borderline personality disorder (BPD; [5]). Indeed, up to 75% of individuals with BPD report attempting suicide at some point in their lifetime [6], with rates of death by suicide approximating 10% [7]. Nonetheless, given the wide variability in the frequency and severity of suicidal behavior within this population, further research is needed

Support for this study was provided in part by R21 DA022383 from the National Institute on Drug Abuse of the National Institutes of Health, awarded to the last author. Location of work: Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, Jackson, Mississippi. ⁎ Corresponding author. Florida State University, Tallahassee, FL 32306-4301. 0010-440X/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.comppsych.2012.04.004

to examine moderators of the relationship between BPD and suicidal behavior. One factor worth examining in this regard is distress tolerance (DT; [8]), defined as the degree to which an individual is able to withstand aversive psychological states [9]. Prior research has found significant associations between low DT and a range of maladaptive behaviors associated with suicide, including deliberate self-harm (DSH; [10]) and substance use ([11]; for a review, see [12]). Further, DT is specifically targeted in dialectical behavior therapy [8] as a method for reducing suicidal behavior among chronically suicidal patients with BPD. However, limited research has examined the association between DT and suicide attempts (or medically severe suicide attempts) specifically. The limited research that has examined the role of DT per se (vs BPD) in suicidality has focused on suicide risk as conceptualized by the interpersonal-psychological theory of suicidal behavior (IPTS; [13]). This theory differentiates between the desire for death by suicide and the capacity to enact lethal self-injury. According to this theory, the presence of suicidal desire alone is not sufficient for serious or lethal suicidal behavior, as an individual must also acquire the capability for suicide (theorized to be comprised of

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habituation to physiological pain and the fear of death). The acquired capability for suicide is thought to develop through repeated exposure to painful and/or provocative events (for a review of the IPTS, see [14]). Although DT was not originally included in the IPTS, recent studies have begun to examine its role within this theory, as well as the nature and extent of its relation to suicide risk. The results of these studies indicate that although low levels of DT predict increased levels of suicidal desire [15,16], high levels of DT predict heightened levels of the acquired capability for suicide [15-17] and physiological pain tolerance [15,16]. These findings suggest that individuals who experience negative emotions as intolerable may be more likely to desire suicide, but less inherently capable of enacting potentially lethal self-injury. Indeed, although individuals with low DT report higher rates of some painful and provocative experiences (one of the factors thought to contribute to the acquired capability for suicide; [13]), it is possible that they are most capable of engaging in behaviors that have a low likelihood of death (eg, DSH) and provide a greater degree of control over how much pain and affective discomfort they must endure prior to accomplishing their desired outcome (eg, decreased negative affect). Along these lines, many of the behaviors associated with low levels of DT (eg, binge eating, alcohol use, cigarette use; eg, [18-20]) are neither painful nor provocative and, as such, are unlikely to contribute directly to the acquired capability. In this sense, many individuals with low DT who engage in highly problematic behaviors may nonetheless fail to develop the acquired capability due to a lack of opportunities to sufficiently habituate to pain and the fear of death. Conversely, high levels of DT may be necessary for someone to persist in the face of innately distressing stimuli (eg, physical pain, fear associated with risk of death) and enact more lethal self-injury. Thus, in line with the IPTS, high DT may be central to the acquired capability for suicide, facilitating persistence through the fear and discomfort associated with suicide attempts. Of course, it is important to note that high DT is likely not inherently maladaptive or associated with heightened suicide risk in and of itself. In the presence of high levels of suicidal desire (such as found within BPD); however, high DT may enable individuals to overcome the intense emotional distress associated with engaging in suicidal behavior. In an effort to help clarify the relationship between DT and suicide risk, we examined the interactive effect of BPD and DT on suicide attempt frequency within a high-risk sample of substance use disorder (SUD) patients in residential treatment. Indeed, SUD patients have been found to exhibit high rates of both BPD [21] and suicide attempts [22], and the presence of BPD among SUD patients has been found to be associated with a number of negative clinical outcomes [23], including worse suicide-related outcomes [24]. Moreover, there is some evidence to suggest higher rates of suicidal behaviors among individuals with cooccurring BPD-SUD (vs either BPD or SUDs alone; [25]).

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We hypothesized that SUD patients with BPD would report more frequent suicide attempts (overall and across varying levels of suicidal intent and medical severity) than those without BPD. Furthermore, we expected that the association between BPD and suicide attempts would be moderated by DT, such that BPD patients with high DT would report a greater frequency of suicide attempts (including medically-severe suicide attempts) than those with low DT. 2. Method 2.1. Subjects Subjects were 176 SUD patients ranging in age from 18 to 61 (mean = 36.12; SD = 10.33). All subjects were recruited from a residential SUD treatment facility in the Jackson, Mississippi area. Subject demographic and clinical characteristics are available in Table 1. 2.2. Measures 2.2.1. Clinical interviews The Structured Clinical Interview for DSM-IV Axis I disorders [26] was used to assess for lifetime and current Axis I disorders, and the BPD module of the Diagnostic Interview for DSM-IV Personality Disorders [27] was used to assess for the presence of BPD. The Diagnostic Interview for DSM-IV Personality Disorders has demonstrated good inter-rater and test-retest reliability [28]. Interviews were conducted by trained bachelors- or masters-level clinical assessors. All interviews were reviewed by a PhD-level psychologist (MTT/KLG), with diagnoses confirmed in consensus meetings. The Lifetime Parasuicide Count (LPC) [29] was used to assess lifetime history of suicidal behaviors. The LPC is a structured interview designed to assess lifetime frequency of suicidal and self-harm behaviors. Participants are asked about the frequency of various forms of self-injury, as well as their intent to die (clear, ambivalent, and none) and the level of medical attention required. Consistent with past research (eg, [30-32]), behaviors are categorized as suicide attempts if participants endorse any intent to die (either ambivalent or clear); behaviors with no intent to die are considered DSH, and were not included in our outcome measure of suicide attempts. The LPC provides a measure of the total number of past suicide attempts, as well as the number of attempts involving ambiguous intent, clear intent to die, and medical attention. Consistent with past research [31,33], all four of these variations in suicidal behavior were utilized as outcomes in this study. 2.2.2. Behavioral tasks The Paced Auditory Serial Addition Task–Computerized Version (PASAT-C; [34]) was used to assess DT. During this task, numbers are sequentially flashed on a computer screen, and subjects are instructed to sum the most recent

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Table 1 Demographic, clinical, and diagnostic data on participants (N = 176) Gender Male Female Race/ethnicity White Black/African American Native American Other Highest level of education High school graduate or less Some college or technical school College graduate Post-graduate education Annual Income N$10,000 $10,000-$49,999 $50,000-$99,999 b$99,999 Marital status Single Married Quit final level of the PASAT-C Lifetime deliberate self-harm a Lifetime mood disorder a Lifetime anxiety disorder a Lifetime alcohol dependence a Lifetime cocaine dependence a Lifetime cannabis dependence a Lifetime opioid dependence a Borderline personality disorder a Suicidal behavior Any suicide attempt a Any ambivalent attempt Any attempt with intent to die a Any medically serious attempt a a

64.2% 35.8% 54.0% 38.1% 5.1% 2.8% 59.1% 33.6% 4.5% 2.8% 46.8% 43.9% 7.0% 2.3% 76.2% 23.8% 68.8% 33.5% 64.2% 45.5% 58.0% 51.1% 32.4% 21.6% 30.1% 15.9% 9.1% 10.8% 10.2%

Percentages reflect the presence of the disorder or behavior.

number with the previous number (using the computer mouse to click on the correct answer). After providing each sum, the participant must ignore the sum and add the following number to the most recently presented number. When a correct answer is provided, a point is obtained. If an incorrect answer is provided, or if the participant fails to provide an answer before the next number is presented, an “explosion” sound is played and the score does not change. The version of the PASAT-C used in this study consisted of 3 levels with increasingly shorter latencies between number presentations (level 1 = 3 seconds; level 2 = 2 seconds; level 3 = 1 second). Because the correct answer must be provided before the presentation of the next number to obtain a point, difficulty increases as latencies decrease. The first level lasted 3 minutes, the second level lasted 5 minutes, and the third level lasted 7 minutes and included an option to terminate the task at any time. Consistent with prior studies [35], DT was indexed by quit status, with individuals who persisted until the end of the task categorized as having high DT and those who quit the task categorized as having low DT. As a manipulation check to ensure that the task induced emotional distress, participants reported on their anxiety,

frustration, and irritation before the task (baseline) and immediately prior to receiving the option to terminate the task using a scale ranging from 0 (not at all) to 100 (extremely). Ratings were highly correlated (rs N .50); consequently, ratings at baseline and prior to the final level of the PASAT were summed to create single scores of emotional distress. In support of the construct validity of the PASAT-C, this task has been shown to induce emotional distress among clinical and nonclinical samples [22,34,36] and to be significantly correlated with self-report measures of the unwillingness to experience distress [37]. Further, providing evidence for its convergent and predictive validity, latency to termination scores on this task have been found to be heightened among SUD patients with (vs without) BPD [22] and to predict residential SUD treatment dropout [38]. Finally, providing support for the construct validity of this task as a measure of the tolerance of distress (vs the level of distress experienced), emotional distress in response to the task is not significantly associated with latency to task termination [39]. 2.2.3. Self-report measures The Deliberate Self-Harm Inventory (DSHI; [40]) is a 17item self-report questionnaire that asks subjects whether and how often they have engaged in a variety of DSH behaviors “intentionally (ie, on purpose).” The DSHI has been found to have adequate test-retest reliability and construct, discriminant, and convergent validity among diverse samples [40,41], including SUD patients [42]. Consistent with past research [40,42], a dichotomous DSH variable was created by assigning a score of “1” to subjects who reported having engaged in DSH, and a score of “0” to subjects who did not endorse any DSH. This variable was included as a covariate to ensure that any observed relations between suicidal behaviors and both DT and BPD were not accounted for by participants' previous history of painful and provocative events [13]. 2.3. Procedure All procedures were approved by the University of Mississippi Medical Center's Institutional Review Board. Data were collected as part of a larger study examining emotion-related factors associated with dropout from residential SUD treatment. After complete description of the study to the subjects, written informed consent was obtained. Inclusion criteria included a Mini-Mental Status Exam [43] score of ≥ 24 and the absence of psychotic symptoms. Eligible patients were recruited no sooner than 72 hours from treatment entry to limit interference of withdrawal symptoms on study engagement. The study protocol was conducted across two separate sessions and subjects were paid $15 for each session. During the initial session, subjects completed the diagnostic interviews. During the second session (approximately four days later), subjects completed a battery of questionnaires and the PASAT-C.

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equation (along with identified covariates) and their interaction term (created by centering and then multiplying the continuous BPD and DT variables; [46]) was entered in the second step. Each of the four suicide attempt outcome variables served as the dependent variables. As with the ANCOVAs, a modified Bonferroni adjustment was applied to the BPD main effect and BPD × DT interaction terms within each analysis. Post-hoc analyses of simple slopes were conducted to probe significant interactions.

2.4. Analysis Following data transformations, we conducted a series of analyses of variance to explore the impact of demographic and diagnostic factors on the independent (DT and BPD) and dependent (suicidal behaviors) variables in order to identify potential covariates for primary analyses [44]. We then conducted a series of 2 (BPD vs non-BPD) × 2 (high vs low DT) analyses of covariance (ANCOVAs), controlling for identified covariates, on each suicidal behavior outcome variable to examine the proposed interactive effect of BPD and DT. The hypothesized main and interactive effects were examined using a modified Bonferroni adjustment to minimize both type I and type II error [45]. Specifically, the P values for these effects were rank ordered by size, with the lowest p value required to exceed the traditional Bonferroni level (.05/K number of analyses) and each subsequent p value required to exceed a level based upon one fewer comparison than the previous (eg, .05/K-1, .05/K-2). Given that significant effects were hypothesized for only BPD and the BPD × DT interaction, corrections were applied to only these variables (which, in turn, were the only variables interpreted in the results), resulting in a total of two comparisons per analysis and eight total comparisons. This method preserves an overall Type I error rate of .05 without increasing the risk for Type II error and unnecessarily reducing statistical power. Post hoc Tukey honestly significant difference (HSD) analyses were conducted to explore the nature of significant interactions. Finally, to further explore these effects, we conducted a series of hierarchical multiple regression analyses using dimensional measures of both DT (ie, latency in seconds to terminate the PASAT-C) and BPD (ie, number of BPD symptoms). In each of the regression analyses, the dimensional measures of DT and BPD symptom count were entered in the first step of the

3. Results 3.1. Variable transformations Descriptive data and intercorrelations for the primary variables of interest are provided in Table 2. All four suicide attempt variables evidenced substantial skew and kurtosis (skewness N5.26, kurtosis N 29.87). Following rank transformation, their skewness (b 3.14) and kurtosis (b 8.71) fell within acceptable levels [47]. Latency to quit the PASAT-C was normally distributed (skewness = 0.50, kurtosis = − 1.62), and 68.8% of the sample chose to quit the PASATC. This rate is consistent with prior work utilizing the PASAT as a measure of DT (eg, [38,48]). For ease of presentation and interpretation, the original means and SDs of these variables before transformation are presented in Table 2; however, all analyses utilized the transformed scores. 3.2. PASAT-C manipulation check Providing support for the use of persistence during the PASAT-C as a measure of the ability to tolerate distress, results of a 2 (BPD vs non-BPD) × 2 (baseline vs pre-quit level) repeated measures analysis of variance for our

Table 2 Means, standard deviations, minimums, maximums, and intercorrelations for variables used in analyses 1 1. Age 2. Gender 3. Lifetime deliberate self-harm a 4. Lifetime alcohol dependence a 5. Lifetime cocaine dependence a 6. Lifetime mood disorder a 7. Lifetime anxiety disorder a 8. PASAT quit 9. BPD status a 10. Total suicide attempts 11. Ambivalent suicide attempts 12. Intent to die suicide attempts 13. Medically-serious attempts Mean/% Yes SD Minimum/# Yes Maximum/# No

2

3

4

5

6

7

8

9

10

11

12

13

– .72⁎⁎ .89⁎⁎ .78⁎⁎ 0.70 b 2.97 0 32

– .44⁎⁎ .51⁎⁎ 0.21 b 1.00 0 9

– .70⁎⁎ 0.54 b 2.38 0 24

– 0.32 b 1.30 0 10

–

.03 – −.16⁎ −.10 – .22⁎⁎ .08 .04 – .30⁎⁎ −.09 .09 .07 .04 .09 −.15 −.06 −.14 −.22⁎⁎ .13 .08 .24⁎⁎ −.07 .01 −.03 −.01 −.31⁎⁎ .16⁎ .18⁎ −.09 −.21⁎⁎ .24⁎⁎ .07 −.07 −.13 .07 .13 −.04 −.20⁎⁎ .26⁎⁎ .05 −.01 −.10 .13 .13 36.12 64.2 male 33.5 58.0 10.33 – – – 18 113 male 59 102 61 63 female 117 74

– −.02 – −.14 −.25⁎⁎ .20⁎⁎ .01 .20⁎⁎ −.18⁎ .15⁎ .07 .13 .08 .15⁎ .04 .12 .07 51.1 64.2 – – 90 113 86 63

– .00 – .25⁎⁎ .02 – .00 −.03 .34⁎⁎ −.05 −.07 .21⁎⁎ .04 −.05 .26⁎⁎ −.03 −.05 .25⁎⁎ 45.5 68.8 30.1 – – – 80 121 53 96 55 123

*P b .05 level; **P b .01 level; SD = standard deviation; PASAT quit = termination status of the PASAT-C (0 = quit, 1 = did not quit); gender: women = 0 and men = 1. a Variables scored such that 0 = absent and 1 = present. b Untransformed mean, standard deviation, minimum, and maximum.

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Table 3 ANCOVAs examining the interactive effect of distress tolerance and BPD on suicide attempts Overall suicide attempts

Model Age Gender DSH Mood disorder Anxiety disorder Cocaine dependence Alcohol dependence Distress tolerance BPD Distress tolerance × BPD

F1,165

P

ηp2

5.01 1.32 3.51 5.87 4.50 1.93 0.55 0.28 2.06 20.20 5.75

.00 .25 .06 .02 .04 .17 .46 .60 .15 .00⁎ .02⁎

0.23 0.01 0.02 0.03 0.03 0.01 0.00 0.00 0.01 0.11 0.03

Ambivalent attempts F1,165 2.59 2.49 2.49 0.02 2.41 2.06 1.14 3.02 2.80 7.31 4.69

Attempts with intent to die

P

ηp2

F1,165

.01 .12 .12 .88 .12 .15 .29 .08 .10 .01⁎ .03

0.13 0.02 0.02 0.00 0.01 0.01 0.01 0.02 0.02 0.04 0.03

3.60 0.00 3.49 8.63 2.73 0.23 0.69 0.01 3.43 9.27 4.66

Medically serious attempt

P

ηp2

F1,165

P

ηp2

.00 .99 .06 .00 .10 .63 .41 .91 .07 .00⁎ .03⁎

0.18 0.00 0.02 0.05 0.02 0.00 0.00 0.00 0.02 0.05 0.03

2.37 0.07 0.62 1.63 2.46 1.38 0.24 1.41 2.03 10.63 3.06

.01 .79 .43 .20 .12 .24 .63 .24 .16 .00⁎ .08

0.13 0.00 0.00 0.01 0.02 0.01 0.00 0.01 0.01 0.06 0.02

⁎ Statistically significant after applying modified Bonferroni adjustment.

composite measure of emotional distress revealed a significant main effect of time, F1,172 = 114.01, ηp2 = 0.40, P b .001), with participants reporting an increase in emotional distress in response to the PASAT-C. The group × time interaction was significant, F1,172 = 4.05, ηp2 = 0.02, P = .05), indicating that the task resulted in a greater mean increase in emotional distress in individuals diagnosed with BPD. 3.3. Selection of covariates None of the independent or dependent variables was significantly associated with race/ethnicity, education, income, or marital status (P N .10). However, frequency of suicide attempts differed significantly as a function of gender, with women reporting a greater frequency of total suicide attempts and attempts with clear intent to die than men (Table 2). Further, participants with (vs without) BPD were more likely to be female than male (χ 2(1) = 17.00, P b .001), younger (t(174) = − 3.21, P = .002) and meet criteria for a lifetime mood disorder (χ 2(1) = 5.80, P = .016), anxiety disorder (χ 2(1) = 10.69, P = .001), alcohol (χ 2(1) = 5.88, P = .015), or cocaine (χ 2(1) = 6.74, P = .009) dependence diagnosis. Further, those with high (vs low) DT were more likely to meet criteria for lifetime cocaine dependence (χ 2(1) = 6.99, P = .008). Finally, there were significant mean differences in lifetime suicide attempts (t(174) = -2.01, P = .046) and suicide attempts with a clear intent to die (t(174) = − 1.98, P = .049) between participants with (vs without) cocaine dependence. Thus, age, gender, lifetime mood disorder, lifetime anxiety disorder, lifetime cocaine dependence, and lifetime alcohol dependence were included as covariates in subsequent analyses. As stated previously, the presence/absence of lifetime DSH was also included as a covariate. 3.4. Primary analyses Consistent with hypotheses, ANCOVA results revealed a significant main effect of BPD across all suicide attempt outcomes and a significant BPD × DT interaction for lifetime number of total suicide attempts and attempts with clear intent to die (see Table 3 and Figures 1-2). Post-hoc Tukey

HSD analyses revealed that SUD patients with both BPD and high DT reported significantly more frequent suicide attempts (overall and with regard to attempts with clear suicidal intent) than all other groups of participants, P b .05. When examining both BPD and DT dimensionally, the same pattern of results was found. Specifically, the overall models predicting each of the suicide attempt outcome variables were significant (F9,166 N 3.06, R 2 N .16, P b .001), and the inclusion of the BPD × DT interaction in the second step of each equation significantly improved the models (R 2Δs N .03, P b .028), accounting for a significant amount of unique variance in each suicidal behavior outcome above and beyond the main effects of BPD symptoms and DT 1. Examination of the simple slopes revealed that the association between BPD symptoms and total lifetime suicide attempts was strongest among those with high (one standard deviation above the mean) DT (b =.18, P b .001), followed by those with mean-level DT (b = .12, P b .001); this association was weakest among those with low (one standard deviation below the mean) DT (b = .07, P b.02). As for the association between BPD symptoms and the remaining three suicide outcomes (ambivalent intent, intent to die, and medically attended attempts), results revealed a significant association only for participants with mean-level (b ≥ .08, P b .001) or high (b ≥ .12, P b.001) DT, and not for participants with low DT (b ≤ .04; nonsignificant). 4. Discussion The primary purpose of this study was to examine the interactive effect of BPD and DT on lifetime frequency of a 1 Findings did not change when the self-harm/suicidality item was omitted from the BPD symptom total score. Likewise, findings remained the same when analyses using both categorical and dimensional variables were conducted without covariates. Finally, the pattern of results remained unchanged for all analyses when emotional distress in response to the PASAT-C was included as a covariate, indicating that the results were reflective of a willingness to persist while experiencing distress rather than simply the level of emotional distress experienced.

M.D. Anestis et al. / Comprehensive Psychiatry 53 (2012) 1208–1216 Distress Tolerance

Total Suicide Attempts (transformed)

.8000

High Low .6000

.4000

.2000

.0000

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desire (ie, SUD patients with BPD), high DT may increase the risk for engagement in suicidal behavior (overall and across varying degrees of intent to die and medical severity). Indeed, whereas low DT may increase the risk for a number of low-lethality maladaptive behaviors that function to avoid emotional distress (eg, substance misuse, DSH), it may protect against engagement in more lethal suicidal behaviors associated with fear, pain, and general discomfort. Individuals with high DT, on the other hand, may be more capable of tolerating the distress associated with suicidal behavior and, in the presence of severe psychopathology associated with heightened suicidal desire (eg, BPD), may be able to engage in behaviors that would otherwise seem too

-.2000 Absent

Threshold

Distress Tolerance

.5000

Distress Tolerance

Attempts with Ambivalent Intent (transformed)

.5000

High Low .4000

.3000

.2000

.1000

Attempts with Intent to Die (transformed)

Borderline Personality Disorder

High Low .4000

.3000

.2000

.1000

.0000

-.1000

.0000

Absent

Threshold

Borderline Personality Disorder

-.1000 Absent

Threshold

Borderline Personality Disorder

range of suicidal behaviors (across level of intent to die and medical severity) within a high-risk population of SUD patients. Results were generally consistent with our hypotheses, providing support for more frequent suicide attempts among BPD patients with high (vs low) DT. Specifically, the interaction of BPD diagnostic status (yes vs no) and the dichotomous DT variable (high vs low) significantly predicted lifetime number of total suicide attempts and attempts with clear intent to die, and the interaction of BPD symptom count and the continuous measure of DT significantly predicted all four suicide attempt outcomes in the expected direction. Although high levels of DT are not likely to be inherently maladaptive, the results of this study suggest that, in the context of a population marked by high levels of suicidal

Medically Serious Attempts (transformed)

Fig. 1. Interaction of distress tolerance and borderline personality disorder diagnostic status predicting total suicide attempts and attempts with ambivalent intent.

Distress Tolerance

.5000

High Low .4000

.3000

.2000

.1000

.0000

-.1000 Absent

Threshold

Borderline Personality Disorder

Fig. 2. Interaction of distress tolerance and borderline personality disorder diagnostic status predicting suicide attempts with intent to die and medically serious suicide attempts.

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painful or difficult. Indeed, behavioral measures of psychological DT, although demonstrating some overlap with selfreport measures of emotional distress tolerance and the acceptance of negative emotions (see [37]), may more accurately be conceptualized as assessing the ability to withstand psychological distress in pursuit of a desired goal (see [48]). Whether that desired goal is ultimately maladaptive or adaptive, and whether it is or is not in the service of emotional avoidance, is not specified. Thus, for individuals who engage in repeated and/or serious suicidal behavior, it is possible that the desire for death outweighs the desire for immediate emotional relief and, as such, high DT manifests as an ability to engage in suicidal behavior despite its affective costs. In this sense, high levels of DT may function in a manner akin to the acquired capability for suicide, theorized to be problematic only in the context of suicidal desire (as the vast majority of individuals with the capacity to enact lethal self-injury will never have the desire to do so). Thus, it is likely those BPD patients with high DT who represent the subset of the population with both the desire and capacity for lethal or serious suicidal behavior. Given that our measure of DT focused on the ability to tolerate psychological distress (vs physical pain), the extent to which BPD-SUD patients with high DT would exhibit elevations in the physiological pain tolerance component of the acquired capability for suicide remains unclear; however, past research has demonstrated significant positive associations between behavioral measures of psychological and physiological distress tolerance (see, eg, [49-51]), suggesting that our measure of psychological DT may also have implications for participants' physiological pain tolerance. Furthermore, high psychological DT has direct relevance to the fear and discomfort likely associated with lethal selfinjury, and the tolerance of the fear of death represents one component of the acquired capability for suicide (see [13]). Although the presence of high DT (as assessed by behavioral measures of the ability to withstand psychological distress in the pursuit of a desired goal) among patients with BPD is relatively uncommon [22,37], it does occur [37], and its relatively rarity may make high DT all that more useful a suicide risk factor to consider within the context of BPD. Just as the presence of high DT in BPD is relatively uncommon, repeated and medically serious suicide attempts are low baserate behaviors and, as such, are likely to be engaged in by only a subset of a population that exhibits an elevation on one or more rare risk factors. As noted above, BPD patients with high DT are not thought to be any less emotionally dysregulated or risky than those with low DT; rather, they may be more likely to persist in attempts to attain specific desired goals (eg, suicide) even when doing so requires temporarily experiencing intensely aversive experiential states (that many people would not have the capacity to tolerate). Of course, this ability to persist through considerable distress may not generalize across all emotions and contexts (a consideration that will need to be addressed in future empirical investigations of suicide risk within this population).

In considering the meaning of these results, it is important to remain cognizant of the study's limitations. Most notably, the correlational data and cross-sectional design preclude determination of the nature and direction of the relationships of interest. Furthermore, the results relied upon the prediction of past suicidal behavior, so it is unclear whether or not these same factors predict future suicide attempts. Studies utilizing longitudinal methodology in the prediction of future suicidal behavior would help clarify the precise interrelations of BPD, DT, and suicidal behaviors. Moreover, effect sizes ranged from small to medium, suggesting that substantial variance in suicidal behaviors remains unaccounted for. In addition, the PASAT-C is a general stressor and, thus, may not induce distress comparable to that experienced in real world contexts. As such, studies that utilize more personally-relevant stressors may produce results with greater generalizability. In addition, in the absence of specific measures of physiological pain tolerance and the acquired capability for suicide, it remains unclear if our proposed mechanism does, in fact, explain the significant relationships noted above. Given past findings of a significant positive association between behavioral measures of psychological and physiological distress tolerance (see [49-51]), as well as research linking high DT to the acquired capability for suicide (see [15,16]), there is reason to believe that our model has merit. However, future studies examining the interrelations of psychological DT, physiological pain tolerance, the acquired capability for suicide, and suicide attempt frequency within the same sample are needed. Likewise, because this study was not designed specifically to test hypotheses stemming from the IPTS, we did not have a measure of suicidal ideation or desire (precluding determination of the presence of heightened suicidal desire among participants with BPD as theorized). Although past research has provided extensive support for heightened suicidal desire among patients with BPD (both in and outside the context of SUDs; eg, [24,52,53]), future research examining the interaction of BPD and DT among SUD patients should include measures of both suicidal desire and behavior in order to provide a more comprehensive test of the IPTS. Furthermore, although a measure of the medical severity and/or lethality (vs frequency) of participants' suicide attempts may arguably be more suitable for testing the principles of the IPTS, past studies of the IPTS have generally relied on measures of suicide attempt frequency (see [54,55]). Furthermore, our specific outcome of medically attended suicide attempts does provide a proxy for more medically serious (and potentially lethal) suicidal behaviors, and, as such, a closer approximation to the suicidal behaviors specified in the IPTS. Finally, given our focus on the presence of cooccurring BPD among SUD patients, the results of this study may not generalize to other BPD samples. Future research should examine the interaction of BPD and DT in the prediction of suicide attempts among outpatient and community BPD samples.

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