Demographic and clinical characteristics
shows that subjects with either ASPD or bipolar disorder were older than controls, and slightly older than subjects with the combination. Educational attainment was lower in subjects with ASPD, whether or not bipolar disorder was also present. Within groups, age and educational attainment of men and women did not differ (P > 0.3).
shows SADS-C factor scores for depression, mania, anxiety, and psychosis. Scores for depression and psychosis were higher in subjects with both bipolar and cluster B disorders than in bipolar disorder alone. Subjects with bipolar disorder included 24 interepisode subjects (did not meet criteria for depressive, manic, or hypomanic episode), 18 manic/hypomanic, 25 depressed, and 19 with combined depression and mania/hypomania. BIS-11 scores did not differ across clinical state [F(3,82) < 2, P > 0.1].
Psychiatric symptom factor scores in bipolar disorder and/or ASPD Bipolar disorder
BIS-11 impulsivity scores
Comparison of bipolar and cluster B disorders
shows BIS-11 scores in subjects with bipolar and/or ASPD and healthy comparison subjects. Bipolar disorder had very large effects on the BIS-11 and its subscales (effect size = 1.45). Effects of ASPD, while significant, were less prominent (effect size = 0.75). Post hoc analysis showed that all groups were different from controls across BIS-11 subscales. Subjects with bipolar disorder without ASPD had significantly higher total, motor, and attentional BIS-11 scores than subjects who had ASPD without bipolar disorder. Subjects with ASPD plus bipolar disorder had higher BIS-11 total, motor, and attentional scores than those with ASPD alone (effect sizes around 0.75). There was a significant interaction between bipolar disorder and ASPD for motor impulsivity; each had higher scores than controls, but the combination did not have higher scores than bipolar disorder alone. Education contributed significantly only to non-planning scores.
BIS-11 Scores in bipolar disorder and ASPD
Age and education had significant effects of their own but did not account for the prominent group differences in BIS-11 scores (). For all subjects, BIS-11 scores did not correlate significantly with age other than a modest correlation (r = 0.152, P = 0.04) with non-planning impulsivity. BIS-11 scores correlated significantly and negatively with education (r = −0.2 to −0.3, P = 0.02–0.001).
Within bipolar disorder, ANOVA revealed no significant differences in BIS-11 scores between subjects with ASPD alone and ASPD plus borderline personality disorder (all F ratios <1).
Psychiatric symptoms and BIS-11 scores
We have reported that BIS-11 scores correlated with SADSC symptom factor scores (38
). SADS-C factor scores in subjects with bipolar disorder were higher than in ASPD or controls. Therefore, we investigated the role of SADS-C factor scores in variation of BIS-11 scores across subject groups using GLM analysis, similar to that in except that SADS-C depression, mania, anxiety, and psychosis factor scores as were added as independent variables. Main effects and interactions involving bipolar disorder and ASPD all persisted. In addition, there were significant effects of depression on BIS-11 total [F
(1,127) = 4.2, P
= 0.043] and non-planning [F
(1,127) = 4.9, P
= 0.028] scores, of anxiety on non-planning scores [F
(1,127) = 4.6, P
= 0.033], and of mania on total [F
(1,127) =5.8, P
= 0.018], non-planning [F
(1,127) = 4.1, P
= 0.045], and motor scores [F
(1,127) = 4.8, P
= 0.03]. Therefore, psychiatric symptoms were related to BIS-11 scores but did not account for the large group differences.
BIS-11 scores and substance-use disorders
Most subjects with either bipolar disorder or ASPD had also met criteria for a substance-use disorder. Because there were no controls without ASPD or bipolar disorder who had a substance-use disorder, substance-use disorder could not be included as an independent variable in the analysis in . ANOVA in subjects without a substance-use disorder revealed results similar to those in , with significant main effects of bipolar disorder [F(1,127) = 24.9, P < 0.0001] and ASPD [F(1,127) = 5.1, P = 0.026] on BIS-11 total score (for the interaction, F = 0). Therefore, substance-use disorder contributed to, but did not completely account for, elevated BIS-11 scores in ASPD or in bipolar disorder. Among subjects with bipolar disorder, BIS-11 scores were higher in those with than without substance-use disorder [total 84.2 ± 13.4 vs. 70.9 ± 13.1, t(63 d.f.) = 4.3, effect size = 1, P < 0.0001]. In ASPD the relationship was similar but weaker, not reaching statistical significance due in part to the smaller number of subjects [68.1 ± 4.9 vs. 63.2 ± 8.6, t(36 d.f.) = 1.4, effect size = 0.6, P = 0.18].
Comorbidities and course of illness
Presence of ASPD and course of bipolar disorder
In subjects with bipolar disorder, comorbid ASPD was associated with history of suicide attempt (17 of 26 subjects with ASPD, vs. 15 of 43 without ASPD, FET = 0.013). ASPD was also associated with increased frequency of drug or alcohol-use disorder (21 of 23 vs. 34 of 51, FET = 0.03).
Co-existing ASPD was significantly related to a history of many manic episodes (15 of 21 with ASPD vs. 14 of 37 without, FET = 0.014) or many depressive episodes (14 of 19 with ASPD vs. 12 of 36 without, FET = 0.005). ASPD was not associated with significantly different age at onset of bipolar disorder (15.1 ± 8.0 years with vs. 18.1 ± 9.4 years without, t = 1.4, P = 0.18).
Relationships between impulsivity and cluster B diagnosis in course of bipolar disorder
We investigated relative contributions of personality disorder diagnosis and BIS scores to course of bipolar disorder using probit analysis. The dependent variable was presence of the characteristic in question, categorical independent variables were personality disorder diagnoses, and continuous independent variables were BIS-11 total score, age, and education. Because a substantial number of subjects with bipolar disorder and ASPD also had borderline personality disorder, both ASPD and borderline personality were included in the model. Because there were no subjects with borderline personality disorder but not ASPD, it was impossible to compute a Wald statistic, so χ2 for type I sum of squares is shown instead. shows that histories of many manic or depressive episodes were related to ASPD and borderline personality disorder, but not BIS-11 score. Comorbid substance-use disorder was related strongly to BIS-11 scores and more weakly, but significantly, to ASPD and borderline personality disorder. History of a suicide attempt was related to presence of either ASPD or borderline personality disorder. Educational attainment contributed (negatively) to histories of many manic episodes and non-alcohol substance abuse.
Relative contributions of BIS-11 Score and personality disorder to course of bipolar disorder
Effect of bipolar disorder on the course of ASPD
In ASPD, substance-related comorbidities were increased with co-existing bipolar disorder compared with subjects with ASPD alone: 20 of 33 subjects without bipolar disorder, vs. 22 of 24 with bipolar disorder, also had an alcohol or other substance-abuse disorder (FET = 0.013). Potential causes include increased impulsivity (), bipolar disorder per se, or the fact that borderline personality disorder was more prevalent in ASPD with than without bipolar disorder (FET = 3.8, P = 0.04), but not bipolar disorder, borderline personality disorder, age, or education (P > 0.3 except age where Wald statistic = 3.2, P = 0.08), contributed to this relationship. There were similar trends for alcohol-use disorder (FET = 0.11) and non-alcohol substance-use disorder (FET = 0.08).
Subjects with ASPD and bipolar disorder were more likely than those with ASPD alone to have made a suicide attempt (one of 26 vs. 17 of 26; FET < 0.001). Probit analysis showed that BIS-11 score (Wald statistic = 7.2, P = 0.008), but not bipolar disorder, borderline personality disorder, age, or education (Wald statistics <1), contributed to this relationship.
Relationship between impulsivity and criminal behaviour
Twenty-eight subjects with bipolar disorder and 34 with ASPD had been convicted of crimes. BIS-11 scores did not differ significantly between those who had or had not been convicted. Of these, eight with bipolar disorder and 15 with ASPD had been convicted of severely violent or destructive crimes. Among subjects convicted for crimes, two-way ANOVA (bipolar disorder vs. ASPD, violent vs. non-violent) revealed main effects of diagnosis for BIS-11 scores [F(1,56) = 12.7, P < 0.001, bipolar disorder higher] but no main effects for type of crime. There was a significant interaction between diagnosis and type of crime for motor impulsivity, which was significantly higher in those with less violent crimes in bipolar disorder [30.6 ± 4.9 vs. 24.8 ± 6, F(1,56) = 8.1, P = 0.006; Tukey Honest Significant Difference = 0.03] but not in ASPD (23.6 ± 3.2 vs. 25.1 ± 5.3).