Common and Specific Abnormalities in Cortical Thickness in Patients with Major Depressive and Bipolar Disorders

Abstract

Major depressive disorder (MDD) and bipolar disorder (BD) are severe psychiatric diseases with overlapping symptomatology. Although previous studies reported abnormal brain structures in MDD or BD patients, the disorder-specific underlying neural mechanisms remain poorly understood. The purpose of this study was to investigate the whole-brain gray matter morphological patterns in unmedicated patients with MDD or BD and to identify the shared and disease-specific brain morphological alterations in these two disorders.We acquired high-resolution brain structural MRI data from a sample of 36 MDD patients, 32 BD patients, and 30 healthy controls. Using FreeSurfer, we estimated their brain cortical thickness (CT) and compared between-group difference in multiple locations across the continuous cortical surface.Compared to the healthy controls, both the MDD and BD patient groups showed significantly reduced CT in the left inferior temporal cortex (ITC). However, compared to the MDD patients, the BD patients showed a significantly thinner CT in the left rostral middle frontal region. In addition, compared to the healthy controls, the BD patients displayed thinner CT in the left ITC, left frontal pole (FPO), left superior frontal, right lateral occipital, right pars triangularis (PTRI) and right lateral orbitofrontal regions. Further analysis revealed a significantly positive correlation between the mean CT in the left FPO and the onset age, but a negative correlation between the mean CT in the right PTRI and the number of episodes, in the BD patients.Our findings revealed that the BD and MDD patients had variations in CT that were in common, but many more that were distinct, suggesting potential differences in their neural mechanisms.

Mood episodes are associated with increased cortical thinning: A longitudinal study of bipolar disorder type II

“…First, consistent with the baseline results, 18 we found thinner cortices in frontotemporal regions in BD type II The present study suggests that depressive episodes are associated with increased thinning of temporal and ventromedial prefrontal cortices. These finding are consistent with some, [12][13][14] but not all, 15,33,34 previous cross-sectional studies of cortical thickness in BD and MDD. In addition, one study of individuals with treatment-resistant depression found that non-remitters had greater frontal cortical thinning than remitters.…”

“…Twenty patients were euthymic (MADRS score <11 and YMRS score <8), three patients were hypomanic (YMRS score 8), nine patients were mildly depressed (MADRS score range[12][13][14][15][16][17][18], and four patients were moderately depressed (MADRS score range[21][22][23][24][25][26][27] at the time of MRI. Patients had lower educational level and higher body mass index (BMI) than HCs.…”

“…11 Two cross-sectional studies of cortical thickness in BD type I and II suggested thinner prefrontal cortices in individuals with higher lifetime number of depressive episodes. 12,13 One cross-sectional study of major depressive disorder (MDD), 14 but not others, 13,15,16 observed a negative association between number of previous depressive episodes and medial prefrontal and temporal cortical thickness. Furthermore, a recent longitudinal study found that individuals with depressive symptoms at baseline had increased thinning in left frontal and bilateral temporal cortices and temporoparietal junctions compared to a control group.…”

The metabolic basis of psychosis in bipolar disorder: A positron emission tomography study

“…These regions have been found to be altered in several psychiatric disorders and in high‐risk individuals . Moreover, recent evidence from structural MRI studies consistently demonstrated the involvement of these structures in BD pathogenesis . Notably, a recent collaborative study from the ENIGMA consortium, employing a sample of over 6,500 individuals, reported significant evidences of reduced occipital cortical thickness, which was also associated with longer duration of illness, in BD patients .…”

“…18 Moreover, recent evidence from structural MRI studies consistently demonstrated the involvement of these structures in BD pathogenesis. 15,19 Notably, a recent collaborative study from the ENIGMA consortium, employing a sample of over 6,500 individuals, reported significant evidences of reduced occipital cortical thickness, which was also associated with longer duration of illness, in BD patients. 15 Similarly, metabolic alterations in occipital areas have been reported in different functional MRI (fMRI) and TA B L E 2 Brain regions showing significant FDG uptake alterations between the three groups of subjects (All P < 0.01 cFWE corrected)…”