Impact of comorbid borderline personality disorder on inpatient treatment for bulimia nervosa: analysis of routine data

BACKGROUND: A substantial rate of patients with bulimia nervosa (BN) also suffer from Borderline personality disorder (BN + BPD). It is widely unknown how these comorbid patients with BN + BPD present and respond to inpatient treatment. Aims of the study were to examine (1) specific characteristics of patients with BN + BPD at admission, discharge, and during treatment, and (2) differential effects of inpatient treatment for BN vs. BN + BPD. METHOD: We analyzed routine data of inpatients admitted for the treatment of BN between 2013 and 2017 in a specialized hospital for eating disorders. (1) Cross-sectional differences were examined with independent t-tests and χ(2)-tests; and (2) treatment effects pertaining to eating disorders symptoms, depression, psychosocial functioning and general psychopathology with repeated measures analysis of variance. RESULTS: Of 1298 inpatients (96% female), 13.2% also had a diagnosis of BPD. (1) Patients with BN + BPD had more previous inpatient treatments (p = 0.001), had a longer length of stay (p = 0.003), gained more weight during treatment (p = 0.006), and were more often irregularly discharged (p = 0.018) as well as rated as unfit to work at discharge (p = 0.003). (2) Both groups improved in all examined variables (all main effects treatment p < 0.001). Patients with BN + BPD showed worse symptoms aggregated across admission and discharge (all main effects diagnosis p < 0.05). Patients with BN + BPD showed smaller improvements (interaction treatment×discharge) in depressive symptoms (p = 0.018), perfectionism (p = 0.009), and asceticism (p = 0.035) and discharge scores mostly lay in the range of the admission scores of the BN-only group. CONCLUSION: Patients with BN + BPD improve during intense and specialized inpatient treatment, yet, retain pronounced impairment at discharge despite longer treatment. Treatment needs to be improved and should focus on transdiagnostic symptoms of BN and BPD. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s40479-018-0098-4) contains supplementary material, which is available to authorized users.