<p>Improvement in interpersonal and defensive functioning are considered central transtheoretical mechanisms that drive symptomatic change in clients with BPD. The current case study illustrates the treatment process and symptom changes in relation to interpersonal functioning, operationalized as the pervasiveness of conflictual relationship themes, and defensive functioning of a 22-year-old female client diagnosed with borderline personality disorder (BPD). The client underwent a 10-session General Psychiatric Management, a psychodynamically-oriented brief case management focusing on interpersonal hypersensitivity, as part of a larger Randomized Controlled Trial. The assessment involved three time points—intake, mid-treatment, and discharge—and comprised of a validated symptom scale, the Zanarini Rating Scale for BPD, along with two coding procedures, the Core Conflictual Relationship Theme method and the Defense Mechanisms Rating Scale-Q sort. While a decrease in the pervasiveness of conflictual relationship themes was observed, a worsening of defensive functioning was noted, which is posited to contribute to the increased symptom severity, particularly in affective and relational domains. Her prominent use of rationalization and passive aggression, along with irregular session attendance and low treatment dosage, are likely key factors influencing the mixed outcomes observed in borderline symptoms and defensive functioning, despite the reduction in the pervasiveness of interpersonal patterns.</p>