Does the comorbidity of borderline personality disorder affect the response to treatment in bipolar patients?

Bipolar disorder (BD) is a highly prevalent condition whose response to pharmacological treatment is associated with a number of factors including psychiatric comorbidity. Borderline personality disorder (BPD) shares clinical symptoms and biological vulnerability with BD and the two conditions are frequently comorbid, thus representing a clinical challenge. The purpose of the present review is to summarize the data related to treatment response in bipolar patients with comorbid BPD. According to systematic review process, a literature search was performed on the PubMed, Embase, PsycInfo, Isi Web of Knowledge, Medscape, and Cochrane Library databases. Peer-reviewed articles until December 2022 were eligible for inclusion. Comorbidity with BPD seems to be associated with a more difficult clinical stabilization in bipolar patients, often requiring poly-therapy or a longer duration of hospitalization. However, three studies, assessing the effectiveness of mood stabilizers in bipolar patients, did not demonstrate a prominent influence of BPD comorbidity in achieving clinical response. The most frequently administered pharmacological treatments in the selected studies include mood stabilizers and atypical antipsychotics. The presence of comorbid BPD in bipolar patients may hamper treatment effectiveness. Future studies, comparing different treatments and with larger samples, are needed to confirm the results critically summarized in the present review.