Are factors associated with death by suicide in people with borderline personality disorder modified by co-occurring depression?

The diagnosis of Borderline Personality Disorder (BPD), which frequently co-occurs with depression, is known to have a high risk of death by suicide. This study explored the contribution of co-occurring depression to factors thought to contribute to death by suicide in people with BPD. Coronial data (2009-2016) included 291 suicide cases where BPD was formally diagnosed (221 with co-occurring depression and 70 without depression). These were compared with depression cases, matched by age, sex, region of usual residence and year of death. The most notable differences were evident between BPD cases (regardless of co-occurring depression) and depression only comparators. These differences included greater prevalence of substance use disorder, psychotic disorders, and anxiety disorders among BPD cases in comparison with depression only (p < 0.05), with psychotic disorders diagnosed most frequently in BPD without depression cases. Service contacts were greater for BPD cases regardless of co-occurring depression, with a wider range of accessed services compared to depression-only cases (p < 0.05) The only exception was for general practitioner contacts, which were lowest for BPD without depression cases. Family, legal, and abuse-related stressors were higher among BPD cases regardless of co-occurring depression. Despite clinical wisdom to the contrary, this evidence suggests that for people with co-occurring BPD and depression, BPD is the dominant condition shaping clinical presentation, service utilisation, and stressor-related experiences prior to death by suicide. The current focus on prioritising depression treatment in people with co-occurring BPD may overlook the broad range of additional suicide-related features associated with BPD.