Functional imaging studies have implicated the orbitofrontal cortex (OFC) in the pathophysiology of borderline personality disorder (BPD). To date, however, volume-based magnetic resonance imaging (MRI) studies have yielded mixed results. We used a surface-based processing approach that allowed us to measure five morphometric cortical features of the OFC, including volumetric (cortical thickness and surface area) and geometric (mean curvature, depth of sulcus, and metric distortion – three indicators of cortical folding) parameters. Participants comprised 25 female BPD patients with no other current psychiatric comorbidity and 25 age- and gender-matched healthy controls who received structural MRI scans. Images were processed using the Freesurfer package. All BPD patients had a history of comorbid psychiatric disorder(s) and were currently on medications. Compared with controls, the BPD group showed reduced cortical thickness, surface area, mean curvature, depth of sulcus, and metric distortion in the right medial OFC. In the left medial OFC, the BPD group had reduced cortical thickness and mean curvature, but increased metric distortion. This study confirmed the utility of surface-based analysis in the study of BPD cortical structures. In addition, we observed extensive structural abnormalities in the medial OFC of female subjects with BPD, findings that were most pronounced in the right OFC, with preliminary data suggesting hemispheric asymmetry.
Borderline personality disorder (BPD) is a devastating condition that affects 1–2% of the population and causes an intense disruption of patients׳ lives and relationships (Minzenberg et al., 2007 and Minzenberg et al., 2008). BPD patients often exhibit emotional instability, impulsive behavior, rapid mood changes, and a propensity toward intense negative emotional states like anger, anxiety and dysphoria (Lis et al., 2007 and Silbersweig et al., 2007).
The orbitofrontal cortex (OFC) is involved in high-level aspects of cognition and emotional behavior (Elliott et al., 2000 and Ongur and Price, 2000). OFC lesions result in emotional dysregulation, along with impulsivity and socially inappropriate behavior (Malloy et al., 1993). In patients with BPD, functional neuroimaging studies have consistently identified abnormal findings in the OFC (Soloff et al., 2000, Soloff et al., 2003, Soloff et al., 2005, New et al., 2007 and New et al., 2009). To date, however, structural magnetic resonance imaging (MRI) investigations have yielded mixed results, with few studies showing reduced OFC volume (Tebartz van Elst et al., 2003, Chanen et al., 2008, Vollm et al., 2009 and Brunner et al., 2010), while others failed to replicate similar findings (Rüsch et al., 2003 and Goodman et al., 2011). Several factors could have contributed to the discrepant results, including the following: (1) differences in the image-processing methods used in the various MRI studies, a factor that is especially important in the context of data indicating a differential effect of BPD on white vs. gray matter or right vs. left hemisphere. (2) Given the putative functional distinction between subregions of the OFC (e.g. medial for emotional processing vs. lateral for cognitive processing) (Elliott et al., 2000 and Ongur and Price, 2000), subregions differences might have confounded region-of-interest analyses. (3) All previously studied MRI cohorts were carried out in BPD patients with a high level of comorbidity with several other psychiatric disorders.
To contribute to the understanding of such discrepancies between the above-mentioned volume-based preliminary findings, we used a well-validated surface-based processing method to measure five geometric parameters of the OFC in a homogeneous group of female BPD patients without psychiatric comorbidities. We hypothesized that the BPD group would present significant OFC alterations, mainly OFC reductions, of all morphometric parameters in comparison with controls. In addition, an exploratory analysis of the morphometrics of the OFC in relationship to the severity of the disorder was also conducted.
Table 1 presents demographic information for the BPD (n=25) and the healthy (n=25) groups; the two groups showed no significant demographic differences. Among BPD patients, the mean (±S.D.) duration of the disorder was 16.6±9.5 years and the mean CGI score (an indicator of the severity of psychiatric disorders) was 3.3±1.8 (range 3–6). Although clinically stable and without fulfilling complete criteria for any current psychiatric comorbidity at the time of the study, all BPD patients had a past psychiatric history, mainly mood disorders (19 patients; 76%). Among them, 13 patients had the diagnosis of major depressive disorder and 6 of bipolar disorder. Other diagnoses were alcohol and drug abuse/dependence (13; 52%) and nonspecific psychotic disorders (9; 36%). Twelve BPD patients (48%) had a history of two or more psychiatric comorbidities. Regarding the number and type of psychotropic medications used, all BPD patients were taking at least one medication (antidepressant, mood stabilizer or antipsychotic) at the time of the study. Twenty-four patients were taking a mood stabilizer, while 18 were taking antidepressants and 10 were using antipsychotics. Six patients were on monotherapy, 13 were taking two medications, and six were on three medications.
