Alliance matters: but how much? A systematic review on therapeutic alliance and outcome in patients with anorexia nervosa and bulimia nervosa

PURPOSE: Patients with eating disorders (ED) pose a high-risk group regarding relapse. The understanding of factors contributing to a better outcome is much-needed. Therapeutic alliance (TA) is one important, pantheoretical variable in the treatment process, which has shown to be connected with outcome. This review looks into a possible predictive effect of TA on outcome as well as related variables. METHODS: A systematic review with pre-determined inclusion criteria following the PRISMA guidelines was conducted for studies published since 2014. Three previous reviews including studies up until 2014 were analyzed for studies matching our inclusion criteria. A total of 26 studies were included. RESULTS: The results were heterogeneous between different patient groups. Regarding the predictive effect of TA, in adolescent samples, the TA of either the patients or their parents seems to impact outcome as well as completion. For adults, results are mixed, with a tendency to a greater impact of TA for anorexia nervosa (AN) patients, while some samples of adult bulimia nervosa (BN) patients did not find any relation between TA and outcome. CONCLUSION: The effect of TA on clinical outcome depends on the patient group. TA has a greater impact on adolescents, irrespective of diagnosis, and on adults with AN. The examined studies have different limitations which include small sample sizes and questionable study design. The examination of motivation as a potential influencing factor is recommended. LEVEL OF EVIDENCE: Level I, systematic review.