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Hippocampal volume in depression — MRCPsych Paper A MCQ

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HardNeuroimaging, neuroendocrinology and psychoneuroimmunologyHippocampal volume in depressionMRCPsych Paper A

A 47-year-old man with recurrent major depressive disorder participates in a case-control MRI study. The study finds that mean hippocampal volume is lower in participants with recurrent depression than in healthy controls. Which interpretation of this finding is most accurate?

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Correct answer: A — A non-specific group-level correlate accentuated in recurrent depressive illness

Explanation lettering: E = shown as A · A = shown as B · D = shown as C · B = shown as D · C = shown as E

E is correct. Large case-control analyses show a small average reduction in hippocampal volume in major depressive disorder, particularly in recurrent illness. Chronic stress, altered hypothalamic–pituitary–adrenal-axis activity and cumulative illness burden are proposed contributors, but cross-sectional MRI cannot establish mechanism or causality. There is substantial overlap between patients and controls, and similar changes occur in other psychiatric disorders, so this is not an individual diagnostic marker. Prion disease requires an appropriate rapidly progressive neurological syndrome and characteristic investigations (A). Reduced volume neither proves irreversible neuronal loss nor predicts inevitable dementia (B). It is not specific to bipolar disorder or capable of distinguishing bipolar from unipolar depression (C). Consequently, it cannot confirm major depressive disorder in an individual patient (D).

Reference: Schmaal L et al. Subcortical brain alterations in major depressive disorder: findings from the ENIGMA Major Depressive Disorder working group. Molecular Psychiatry. 2016;21:806–812. https://pubmed.ncbi.nlm.nih.gov/26122586/