2026 ECNP Congress

PS04-4069

Does comorbid borderline personality disorder worsen healthcare utilization and hospitalization outcomes in bipolar disorder? A nationwide retrospective study

Mariana Viana Neto — A.R. Ferreira, M. Gonçalves-Pinho, R. Barranha, A. Freitas, L. Fernandes · Faculty of Medicine- University of Porto- Porto- Portugal, Faculty of Medicine- University of Porto- Porto- Portugal, Porto- Portugal, Portugal

2026 ECNP Congress

Background: Bipolar disorder (BD) and borderline personality disorder (BPD) are distinct but frequently co-occurring psychiatric disorders with substantial clinical overlap, including affective instability, impulsivity, and increased risk of self-harm [1]. Although their expected co-occurrence in the general population is low, observed rates are substantially higher, and the nature of their relationship remains a matter of ongoing debate [2]. Clinically, BD-BPD comorbidity defines a subgroup with a more severe and unstable illness course, including earlier onset of mood symptoms, greater psychiatric comorbidity, higher suicide risk, poorer treatment adherence, and increased hospitalization rates [2-5]. However, large-scale studies evaluating the impact of BD-BPD comorbidity on real-world inpatient outcomes remain limited. This study therefore aimed to examine whether comorbid BPD identifies a subgroup of BD hospitalizations with distinct patterns of healthcare utilization and inpatient outcomes.

Methods: A retrospective study was conducted using a nationwide administrative database comprising all public hospital admissions in mainland Portugal. Hospitalizations involving adults with a primary or secondary diagnosis of BD between 2008 and 2015 were identified. Comorbid BPD was defined using ICD-9-CM code 301.83 and BD and BPD groups were compared. Outcomes included length of stay (LoS), discharge against medical advice (DAMA), estimated hospital charges, electroconvulsive therapy (ECT) use, and readmissions at 30 days and 1 year. Multivariable regression models adjusted for age, sex, and Charlson Comorbidity Index were used to assess DAMA and readmission outcomes.

Results: A total of 32,610 BD hospitalizations were identified, of which 342 involved comorbid BPD. Compared with BD alone, comorbid cases involved significantly younger patients (mean age 39.29 vs 51.56 years; p <0.001) and more women (75.4% vs 65.9%; p <0.001). LoS did not differ significantly between groups. However, comorbid BPD was associated with higher odds of DAMA (aOR=1.59; 95% CI: 1.02–2.47) and increased risk of 1-year readmission (aOR=1.34; 95% CI: 1.07–1.69), but not 30-day readmission. Hospitalizations with comorbid BPD were more frequently urgent and more often involved depressive, mixed, and unspecified episodes. Psychiatric comorbidities were significantly more frequent in the comorbid group (51.8% vs 28.2%; p <0.001), particularly substance-related and suicide-related conditions. Despite this, estimated hospital charges were lower, and ECT was less frequently used.

Conclusions: Comorbid BPD in BD identifies a clinically distinct and higher-risk subgroup characterised by greater psychiatric complexity and increased longer-term hospital utilization. In this nationwide study, comorbidity was associated with higher rates of DAMA and increased risk of 1-year readmission, despite similar LoS and lower estimated hospital charges. These findings suggest that the impact of BD-BPD comorbidity may not be fully captured by conventional inpatient resource use indicators but is instead reflected in greater clinical instability and poorer continuity of care. Recognizing this high-risk subgroup has important implications for risk stratification and highlights the need for integrated inpatient and post-discharge management strategies targeting both acute symptom stabilization and longitudinal care continuity.

References

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