Hippocampal and amygdala volumes in an older bipolar disorder sample

Brain volumetric magnetic resonance imaging (MRI) studies of adult bipolar disorder samples, compared with healthy controls, have reported conflicting results in hippocampal and amygdala volumes. Among these, few have studied older bipolar samples, which would allow for examination of the effects of greater duration in mood episodes on brain volumes. The aim of this study was to compare hippocampal and amygdala volumes in older bipolar patients with controls.

High-resolution MRI scans were used to determine hippocampal and amygdala volumes that were manually traced using established protocols in 18 euthymic patients with DSM-IV bipolar I disorder (mean age 57 years) and 21 healthy controls (mean age 61 years). Analysis of covariance (ANCOVA) was used to explore group differences while controlling for intracranial volume (ICV), age, sex, and years of education.

While gray matter, white matter, and cerebrospinal fluid volumes did not differ between the groups, bipolar disorder patients had smaller ICV (t = 2.54, p = 0.015). After correcting for ICV, the bipolar group had smaller hippocampal (left hippocampus F = 13.944, p = 0.001; right hippocampus F = 10.976, p = 0.002; total hippocampus F = 13.566; p = 0.001) and right amygdala (F = 13.317, p = 0.001) volumes. Total hippocampal volume was negatively associated with the duration of depressive (r = -0.636; p = 0.035) and manic (r = -0.659; p = 0.027) episodes, but not lithium use. Amygdala volumes were not associated with the duration of mood episodes.

Older bipolar disorder patients had smaller hippocampal and amygdala volumes. That smaller hippocampal volume was associated with the duration of mood episodes may suggest a neuroprogressive course related to the severity of the disorder.