Impact of comorbid borderline personality disorder on the outcome of inpatient treatment for anorexia nervosa: a retrospective chart review

BACKGROUND: Data on patients with anorexia nervosa (AN) and comorbid Borderline personality disorder (AN+BPD) are scarce. Therefore, we investigated (1) whether patients with AN and AN+BPD differ in characteristics related to admission to, discharge from, and course of specialized inpatient eating disorder treatment and (2) how comorbid BPD affects treatment outcome. METHOD: One-thousand one-hundred and sixty inpatients with AN (97.2% female, 5.9% with comorbid BPD; mean age = 26.15, SD = 9.41) were administered the Brief Symptom Inventory (BSI), the Eating Disorder Inventory 2 (EDI-2), and the Global Assessment of Functioning (GAF) at admission and discharge. Data were extracted by a retrospective chart review of naturalistic treatment data. Age, sex, weekly weight gain, length of stay, and discharge characteristics were compared with independent t-tests and χ(2)-tests. Changes in outcome variables, including body mass index (BMI), were analyzed with longitudinal multilevel mixed-effects models. RESULTS: No differences in age or sex were found between patients with AN and AN+BPD, but groups differed in previous inpatient treatments, BMI at admission, and frequency of at least one additional comorbidity with higher values for AN+BPD. Higher levels of disorder-specific and general psychopathology at admission were found for AN+BPD. Patients with AN showed statistically significant improvement in all examined variables, patients with AN+BPD improved in all variables except EDI-2 body dissatisfaction. Strongest improvements in patients with AN+BPD occurred in BMI (Cohen’s d = 1.08), EDI-2 total score (Cohen’s d = 0.99), EDI-2 interpersonal distrust (d = 0.84). Significant Group x Time Interactions were observed for BSI GSI, GAF, and EDI-2 body dissatisfaction, indicating a reduced benefit from inpatient treatment in AN+BPD. At discharge, no differences were found in weekly weight gain, BMI, length of stay, or discharge characteristics (e.g., ability to work, reason for discharge), however, patients with AN+BPD were more frequently treated with medication. CONCLUSIONS: Patients with AN+BPD differ from patients with AN in that they show higher general and specific eating disorder psychopathology and only partially improve under specialized inpatient treatment. In particular, aspects of emotion regulation and core AN symptoms like body dissatisfaction and perfectionism need to be even more targeted in comorbid patients. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40479-021-00149-7.