Structural brain abnormalities of the medial temporal lobe have been found in people with bipolar disorder (BPD). It is not known whether these abnormalities progress over the course of the illness.

We conducted a prospective cohort study of 20 patients with bipolar disorder and 21 control subjects recruited from the community. Participants were group matched for age, sex and premorbid IQ. Longitudinal change in grey matter density was evaluated using the technique of tensor based morphometry (TBM) in SPM2.Changes in grey and white matter density were estimated and compared to changes in cognitive function and clinical outcome.

Patients with bipolar disorder showed a larger decline in hippocampal, fusiform and cerebellar grey matter density over 4 years than controls. No significant changes in white matter density were found. Reductions in temporal lobe grey matter correlated with decline in intellectual function and with global assessment of functioning. No associations were found with medication.

Patients with bipolar disorder lose hippocampal, fusiform and cerebellar grey matter at an accelerated rate compared to healthy controls. This tissue loss is associated with a corresponding deterioration in cognitive function.