Amygdala volume reduced in schizophrenia, not psychotic BD

By Mark Cowen

Amygdala volume is reduced in patients with schizophrenia compared with those who have psychotic bipolar disorder (BD), researchers report.

In contrast, the team found that patients with psychotic BD show no significant amygdala volume deficits compared with healthy controls.

"These results suggest that change in volume of amygdala may represent a morphologic feature distinguishing BD subjects from subjects with schizophrenia, even though psychotic symptoms can be found in both," comment Pamela Belmonte Mahon (Johns Hopkins School of Medicine, Baltimore, Maryland, USA) and colleagues.

The findings come from a study of 31 schizophrenia patients, 36 psychotic BD patients, and 27 mentally healthy controls, with no significant age or gender differences between the groups.

Magnetic resonance imaging scans revealed that mean amygdala volume was 1.91 cm³ in schizophrenia patients, 2.07 cm³ in psychotic BD patients, and 2.05 mm³ in controls.

After accounting for total intracranial volume, age, and gender, the team found that mean amygdala volume was significantly reduced in schizophrenia patients compared with psychotic BD patients, at an adjusted mean difference of 51.4 mm³.

The adjusted mean difference between psychotic BD patients and controls, at 9.1 mm³, was not significant.

Writing in Schizophrenia Research, the researchers note that previous studies have reported larger amygdala volumes in BD compared with schizophrenia patients, but few have specifically investigated amygdala volumes in BD patients with psychosis.

"In this context, studying psychotic bipolar disorder is of special interest as it has symptomatic overlap with schizophrenia as well as potentially a shared genetic etiology," comment Mahon et al.

They conclude: "While the nature of abnormalities of the amygdala in BD and schizophrenia differ, this brain region might still be the locus of a partially shared pathophysiology between these disorders."

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