Introduction: In this study, we mainly evaluated the associations of borderline personality disorder (BPD), neuroticism, and childhood trauma with the self-rated and clinician-rated overall functional impairment levels of adult euthymic patients with bipolar disorder-1 (BD-1). In addition, we compared patient and healthy control groups regarding the levels of of childhood trauma, neuroticism, BPD and functional impairment. Methods: In total, 90 euthymic BD-1 patients and 90 healthy controls were enrolled. The Childhood Trauma Questionnaire-Short Form, the neuroticism subscale of the Eysenck Personality Questionnaire Revised-Abbreviated Form, the Borderline Personality Questionnaire, the Functioning Assessment Short Test, and the Sheehan Disability Scale were administered to the participants. Results: The study revealed that the levels of BPD, neuroticism, emotional abuse, physical abuse, global childhood trauma, self-rated overall functional impairment, all the subdomains of self-rated functional impairment, clinician-rated overall functional impairment, and all the subdomains of clinician-rated functional impairment (except leisure time) were significantly higher in the patients than those in the healthy controls (p < 0.05). Clinician-rated functional impairment levels were significantly correlated with levels of BPD (r = 0.555, p<0.001), neuroticism (r = 0.429, p < 0.001), global childhood trauma (r = 0.391, p <0.001), and all subtypes of childhood trauma except sexual abuse. Self-rated functional impairment levels were significantly correlated with levels of neuroticism (r= 0.289, p = 0.006), physical neglect (r = 0.213, p = 0.044), and BPD (r = 0.557, p < 0.001). In the regression analyses, the self-rated overall functional impairment levels were only significantly associated with the BPD feature levels (beta = 0.319, p < 0.001) and the clinician-rated overall functional impairment levels were only significantly associated with the BPD feature levels (beta = 0.518, p < 0.001). Conclusion: The present study's findings suggest that BPD features should be addressed in psychosocial interventions aimed at ameliorating functional impairment in patients with BD-1. Only BPD features were associated with self-rated and clinician-rated overall functional impairment levels in the regression analyses in the BD-1 patients. Performing self-rated and clinician-rated functional impairment assessments in the same clinical trial may give rise to relevant findings in the future.
