Anger instability and aggression in Borderline Personality Disorder - an ecological momentary assessment study.

Background: Anger and aggression are core features of Borderline Personality Disorder (BPD), contributing strongly to the individual as well as the societal burden caused by the disorder. Across studies, patients with BPD have shown increased, more frequent and prolonged episodes of anger and reported an increased prevalence of reactive aggression. However, only a few studies have investigated anger and aggression in the patients' everyday lives and did not consider anger instability. In order to contribute knowledge about aggression and its association with anger intensity and anger instability in real-life in BPD the aim of the present study was to better characterize days with and without aggressive behaviors with regard to the patients' experienced anger.

Methods: Patients with BPD and high aggression as well as healthy participants took part in an ecological momentary assessment (EMA) study assessing state anger and aggression three times per day over two weeks. Multilevel modeling was conducted and anger instability was operationalized by squared successive differences.

Results: As expected, patients with BPD reported greater instability in their experienced anger compared to healthy participants. Most interestingly, in the BPD group the occurrence of aggressive behavior was significantly associated with anger intensity as well as anger instability. More precisely, on days when patients with BPD acted out aggressively, they reported higher anger intensity as well as greater anger instability than on days when they did not act out aggressively.

Conclusion: Knowledge about what characterizes days with aggressive behaviors may help to improve interventions to reduce aggressive behavior and thus relieve the burden aggression causes for patients with BPD, their surroundings and society.