Global hippocampal atrophy in major depressive disorder: a meta-analysis of magnetic resonance imaging studies

Major depressive disorder (MDD), an incapacitating mental disorder, is characterized by episodes of at least 2 weeks of apparent changes in mood, cognition, and neurovegetative functions. Many neuroimaging studies using magnetic resonance imaging (MRI) have examined morphometric changes in patients with MDD, but the results are not conclusive. This study aims to review the literature and perform a meta-analysis on hippocampal volume (HcV) in patients with MDD. Studies on HcV in patients with MDD diagnosis were identified from major databases (MEDLINE, EMBASE, The Cochrane Library, Scopus, PsycINFO, and SciELO) using the search terms depression, major depressive disorder, MDD, unipolar, magnetic resonance imaging, MRI, and hippocampus. A meta-analysis of 29 studies fulfilling specific criteria was performed. The sample included 1327 patients and 1004 healthy participants. The studies were highly heterogeneous with respect to age, sex, age of onset, and average illness duration. However, the pooled effect size of depression was significant in both hippocampi. MDD was associated with right (-0.43; 95% confidence interval [95%CI] -0.66 to -0.21) and left (-0.40; 95%CI -0.66 to -0.15) hippocampal atrophy. MDD seems to be associated with global HcV atrophy. Larger longitudinal follow-up studies designed to analyze the influence of sociodemographic variables on this relationship are required to yield better evidence about this topic.