Hirnstrukturelle Assoziationen suizidaler Phänotypen bei vorliegener Diagnose einer Major Depressive Disorder
Abstract
Unipolar depression is one of the most common mental illnesses worldwide and is associated with considerable individual and social burdens. Of particular relevance is suicidality, which includes suicidal thoughts, plans and attempts. Despite the established assumption that depression is a risk factor for suicidality, little is known about the aetiology and neurobiology of suicidality, which makes it difficult to predict future suicidal acts. Previous studies on the neurobiological and structural correlates of different levels of suicidality in depressive patients have revealed changes in various transmitter systems, associations with inflammatory processes and structural differences. These were most frequently reported in the areas of the prefrontal cortex, the insula, the basal ganglia, the thalamus and the temporal lobes. However, the state of research to date must be regarded as heterogeneous overall and provides partly contradictory results. Further research in this area is therefore necessary.
The present study addresses this need and used voxel-based and surface-based morphometry as well as diffusion tensor imaging to investigate neurostructural correlates in depressive patients with different degrees of suicidality. Changes in grey matter volume (GMV), cortical thickness and white matter integrity indicated by fractional anisotropy (FA) were analyzed, particularly in the prefrontal cortex and adjacent areas and fiber tracts. The German version of the SBQ-R was used to determine suicidality and to classify suicidality levels. The analyses were divided into two approaches. In the dimensional approach, a linear regression was used to investigate the correlation of neurostructural correlates with increasing suicidality in n=236 depressive patients (GMV, cortical thickness) and n=200 depressive patients (FA). In addition, an analysis was conducted using a categorical approach, in which an ANOVA was used to compare the subgroups nSB (non-suicidal behavior), SI (suicidal ideation) and SA (suicide attempt) in n=96 depressive patients (GMV, cortical thickness) and n=81 depressive patients (FA).
In the context of the dimensional approach, there were no significant correlations of GMV or cortical thickness with an increasing degree of suicidality.
However, regarding the categorical approach, differences in GMV were observed in the group comparison SA>SI in areas of the temporal and parietal lobe as well as the thalamus of the left hemisphere.
The described GMV difference in the temporal lobe could be assigned more closely to the fusiform gyrus and inferior temporal gyrus. Structural changes in these areas have hardly been investigated to date. Previous studies have mainly focused on functional correlations, but the results appear plausible in view of the assigned function of the affected brain regions and support the described changes in functional connectivity. The GMV difference found in the parietal lobe affected the supramarginal gyrus, the postcentral gyrus and the parietal operculum. Previous findings from imaging studies confirm functional and structural changes, thus supporting the involvement of these regions and suggesting that this could represent a neurobiological basis of suicidal behavior in depression.
The findings described in thalamus fit into a series of inconsistent study results regarding volumetric, structural and functional changes, which, however, point to an overall involvement of the thalamus in suicidal behavior.
No significant group differences in cortical thickness were observed.
When investigating the FA, a negative correlation with an increasing degree of suicidal behavior was observed in different neural pathways. In the right hemisphere, significant effects were observed in the anterior thalamic radiatio (ATR), the corticospinal tract (CST), the superior longitudinal fasciculus (FLS) and the superior temporal fasciculus (FLST). Significant left hemispheric effects were found in the CST, FLS and FLST. There were also group differences regarding the FA of the right hemispheric ATR and the bilateral CST when comparing SA
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