Subregional hippocampal deformations in major depressive disorder

Background: Hippocampal atrophy is a well reported feature of major depressive disorder, although the evidence has been mixed. The present study sought to examine hippocampal volume and subregional morphology in patients with major depressive disorder, who were all medication-free and in an acute depressive episode of moderate severity.

Methods: Structural magnetic resonance imaging scans were acquired in 37 patients (mean age 42 years) and 37 age, gender and IQ-matched healthy individuals. Hippocampal volume and subregional structural differences were measured by manual tracings and identification of homologous surface points to the central core of each hippocampus.

Results: Both right (P=0.001) and left (P=0.005) hippocampal volumes were reduced in patients relative to healthy controls (n=37 patients and n=37 controls), while only the right hippocampus (P=0.016) showed a reduced volume in a subgroup of first-episode depression patients (n=13) relative to healthy controls. Shape analysis localised the subregional deformations to the subiculum and CA1 subfield extending into the CA2-3 subfields predominantly in the tail regions in the right (P=0.017) and left (P=0.011) hippocampi.

Limitations: As all patients were in an acute depressive episode, effects associated with depressive state cannot be distinguished from trait effects.

Conclusions: Subregional hippocampal deficits are present early in the course of major depression. The deformations may reflect structural correlates underlying functional memory impairments and distinguish depression from other psychiatric disorders.