Case formulation in interpersonal defence theory: A process model of interpersonal phenomena that play key roles in psychopathology and psychotherapy

Interpersonal defence theory (e.g., Westerman, 2018a; Westerman & Muran, 2017; Westerman & Steen, 2007) is an interpersonal approach to psychopathology that is well suited for research and practice with patients with personality disorders. Case formulations of a novel kind play an integral role in the theory. The theory and its case formulations provide process models of interpersonal phenomena. As a result, they offer explanatory models that enhance understanding of problematic processes and have implications for psychotherapy. This chapter presents the theory, discusses procedures clinicians and researchers can employ for arriving at case formulations based on the theory, illustrates the theory’s tenets and the case formulations it calls for with a clinical example, summarizes studies based on interpersonal defence theory that have been conducted of therapy with patients with personality disorders, and discusses the theory’s implications for psychotherapy that are most closely linked to its approach to case formulation.