Hippocampal volume measurement in older adults with bipolar disorder.

Objective: Decreased hippocampal volumes have been noted in unipolar depressed subjects, especially in elderly patients and those with cognitive impairment. Initial studies of mixed-aged bipolar subjects and controls have had conflicting findings, with most noting no difference; however this region has not been examined in older bipolar subjects.

Methods: The authors examined the hippocampal volumes of 36 older bipolar subjects (mean age: 58 years) and 29 older normal-comparison (NC) subjects (mean age: 61), using logistic-regression analyses to control for age and gender. Differences between late- and early-onset (before age 45) bipolar subjects were also examined.

Results: The left hippocampus was noted to be enlarged in older bipolar subjects, compared with the older NC group (sex and age controlled). No differences were noted in hippocampal volumes by age at onset nor number of previous episodes. The increase in hippocampal volume may be associated with the use of lithium, but not valproic acid.

Conclusions: Left-hippocampal volume is increased in older bipolar subjects compared with NC subjects. The differences were not explained by age at onset, current mood state, or cognitive status, but may be associated with exposure to lithium. This finding would support previous observations about the neural-plasticity effect of lithium.