Hippocampal volume and subcortical white matter lesions in late life depression: comparison of early and late onset depression

Background: Reduced hippocampal volume and increased prevalence of subcortical white matter lesions are associated with both recurrent early onset depression (EOD) and late onset depression (LOD). It is not clear whether these two factors differentially affect the age of onset of first depression. Therefore, we wished to investigate the relationship between age of first depression onset and hippocampal volume, with adjustment for subcortical white matter lesions. Methods: MRI brain scans were used to compare hippocampal volumes and white matter lesions between age matched female patients (> 60 years) with recurrent EOD and LOD and healthy controls. Results: When comparing the three groups and adjusting for age, the Mini-Mental State Examination score, total brain volume and total hippocampal volume were significantly smaller in patients with EOD compared with controls (5.6 vs 6.1 ml; p = 0.04). The prevalence of larger subcortical white matter lesions was higher in patients with LOD compared with patients with EOD (47% vs 8%; p = 0.002). Patients with LOD did not differ in hippocampal volume from patients with EOD or from controls. Conclusions: In late life depression, age of first depression onset may distinguish between different independent neuropathological mechanisms. A small hippocampus volume may be a neuranatomical marker of EOD depression and larger subcortical white matter lesions could be an intermediate between cerebrovascular disease and LOD.