MedWire News: There are subtle but significant differences in gray matter (GM) architecture between patients with bipolar disorder and those with major depressive disorder (MDD) who both present with psychotic features at a similar early disease stage, study results show.
"These findings reinforce the view that there are important pathophysiological distinctions between bipolar disorder and MDD, and indicate that subtle dorsal anterior cingulate abnormalities may be relevant to the pathophysiology of bipolar disorder," Cintia Perico (University of São Paulo, Brazil) and colleagues comment in the journal Bipolar Disorders.
Several morphometric magnetic resonance imaging (MRI) studies to date have investigated the presence of brain volumetric and GM density abnormalities in adult patients suffering from bipolar disorder.
Recently, a minority of MRI studies of bipolar disorder have focused on the recruitment of patients early during the course of their illnesses, in order to avoid the confounding influence of chronic drug treatments and the impact of repeated disease episodes on measurements of regional brain volumes.
Also, no MRI study to date has conducted direct comparisons between patients with recent-onset bipolar disorder and MDD recruited from the same environment and at similar disease stages - which would be "highly relevant to clarify the neurobiological substrates underlying each of those two conditions," say Perico et al.
In the current study, the researchers conducted a population-based morphometric MRI study in which patients with first-episode psychosis (FEP) were recruited in a circumscribed region of São Paulo. Of the original cohort, 46 were confirmed as having affective psychosis, 26 bipolar disorder and 20 MDD. In addition 94 mentally healthy controls were examined using identical techniques.
The bipolar disorder group showed increased volume of the right dorsal anterior cingulate cortex relative to controls, while the MDD patients exhibited bilateral foci GM deficits in the dorsolateral prefrontal cortex.
Direct comparison between bipolar disorder and MDD patients showed a focus of GM reduction in the right-sided dorsolateral prefrontal cortex and a trend toward left-sided GM deficits in the dorsolateral prefrontal cortex of MDD patients.
When analyses were repeated with scanner site as a confounding covariate, the finding of increased right anterior cingulate volumes in bipolar disorder patients relative to controls remained statistically significant.
Perico et al explain that this region is a critical component of the dorsal cortical network that mediates cognitive control aspects of emotion, in connection with the prefrontal cortex and hippocampus. Consequently, localized abnormalities of the dorsal anterior cingulate cortex may play a relevant role in the cognitive deficits associated with mania.
The researchers conclude that studies with a similar methodology "are warranted in order to further ascertain whether our findings can be extended to mood disorders in general, rather than being specific to the population of recent-onset affective disorder patients presenting with psychotic features."
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