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Abstract

Borderline personality disorder (BPD) has its onset in adolescence or early adulthood and is frequently accompanied by nonsuicidal self-injury (NSSI), which is a common phenomenon in adolescence and may be viewed as a disorder in its own right. While BPD has been studied extensively in the past decades, NSSI has just recently been added as a condition for further study to the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 2013). For BPD, Linehan (1993) postulated based on her biosocial theory that emotion dysregulation arises from interactions between biological vulnerabilities and environmental influences. Put differently, Linehan claimed that adverse childhood experiences aggravate biological stress responses and vice versa. Biological stress responses are for instance mirrored by aberrant endocrinological functioning. The biosocial theory has been extended by Crowell et al. (2009) to focus on developmental psychopathology and trait impulsivity in BPD. For NSSI, a temporal framework has recently been proposed by Kaess et al. (2021) to distinguish relevant traits (proximal biological correlates and distal risk factors) and states (biological mechanisms before, during or after NSSI incidents) underlying NSSI. Based on this categorization, the temporal framework aims at differentiating mechanisms and risk factors underlying behaviors, cognitions, and emotions characteristic for NSSI. The current dissertation evaluated both theoretical approaches with regard to development and maintenance of BPD and NSSI by focusing on endocrinological markers of the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-thyroid (HPT) axes. These endocrinological axes were investigated as they may mirror stress responses adequately and as corresponding imbalances have been interpreted as warning signs for the development of several psychopathologies. According to this, a meta-analysis was performed in Study 1 to systematically investigate altered HPA axis functioning in BPD patients. Adult BPD patients were compared to healthy and clinical controls based on several experimental paradigms. Findings indicated blunted cortisol responses to psychosocial stressors and elevated continuous cortisol in BPD patients. To examine endocrine concomitants of development and aging in BPD more closely, Study 2 focused on the so-called cortisol awakening response (CAR) in female adolescents and adults with BPD compared to healthy controls. Here, findings showed increased CARs in BPD patients. Positive correlations between age and CAR in BPD patients further suggested that endocrine alterations may amplify with increasing age and chronification of the disorder. To expand the empirical evidence for endocrine markers in BPD and NSSI, Study 3 focused on HPT axis markers and cortisol in adolescents with NSSI and showing a variable number of BPD symptoms. In addition to cortisol, thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), and the ratio of these hormones (fT3/fT4 ratio) were examined and compared to markers obtained from healthy adolescents. Endocrine markers were further correlated with focal psychopathological measures to allow for a dimensional perspective on biological stress responses in NSSI patients. Here, altered HPT axis functioning in NSSI patients showed through lower fT3/fT4 ratio values. Besides, negative correlations between fT3, fT3/fT4 ratio and severity of BPD symptoms, depression scores and symptomatic distress were observed. Lastly, TSH correlated negatively with severity of BPD symptoms and symptomatic distress. In brief, the current dissertation affirms several premises of the biosocial theory for BPD and the temporal framework for NSSI by showing that altered endocrinological functioning depends on several factors such as developmental psychopathology and symptom severity. Yet, findings also suggest that more research on potential mediators, such as adverse childhood experiences, is needed before endocrinological markers can be used to implement and evaluate personalized treatments. Nonetheless, the current dissertation contributes to a comprehensive characterization of HPA and HPT axis markers in BPD and NSSI patients, which is why these markers may eventually be used as reliable and change-sensitive measurements in future therapy research and clinical practice.