Abstract
Major Depressive Disorder (MDD) is a serious and impactful mental disorder that is predicted to be the leading cause of global disability by 2030. Borderline Personality Disorder (BPD) is frequently diagnosed alongside MDD and contributes to the deleterious impact to individuals’ lives. In the presence of comorbid BPD, first-option treatment efforts for MDD are often hindered, recovery is often longer, and those diagnosed exhibit greater levels of self-harm and suicidal behaviours than either disorder on its own. Network Theory and its application, Network Analysis, provide a novel approach to conceptualising and understanding the comorbidity between MDD and BPD. The aim of this thesis was to explore the symptom overlap between the two disorders using Network Analysis.
Five hundred and forty-eight participants’ data were pooled from four clinical trials run between 1994 and 2013 at the Department of Psychological Medicine, University of Otago, Christchurch. All participants were diagnosed with a current Major Depressive Episode (as part of MDD or Bipolar II). Baseline MDD and BPD symptom data from entry assessments were input into a cross-sectional Network Analysis. A further Network Analysis was estimated with the addition of three pertinent covariates alongside the MDD and BPD symptoms.
The Network Analyses identified several connecting symptoms that bridged between MDD and BPD. An important finding from this thesis was that after controlling for depression severity, the BPD symptoms of identity disturbance and unstable relationships had unique and robust relationships with MDD suicidal ideation and behaviours. Upon further exploration of these bridge relationships, it was found that participants who exhibited identity disturbance were almost three times more likely to have reported a previous suicide attempt.
The results from this thesis are of particular clinical interest to risk assessment and treatment of individuals with comorbid MDD and BPD. Further, this thesis highlights the importance of exploratory investigations into the clinical implications of findings from Network Models, in addition to examining the impact of transdiagnostic symptoms in individuals with primary Mood Disorders.