Clinical meaning
Late-life depression (LLD) affects 1-5% of community-dwelling elderly (major depression) and up to 15% for subsyndromal depressive symptoms, rising to 25-30% in nursing facility residents. LLD has distinct neurobiological features compared to early-onset depression: cerebrovascular disease contributes to 'vascular depression' (white matter hyperintensities on MRI disrupt frontal-subcortical circuits involved in mood regulation), neuroinflammation (elevated IL-6, TNF-alpha, CRP), HPA axis dysregulation (cortisol elevation causing hippocampal atrophy), and reduced neuroplasticity (decreased BDNF, impaired neurogenesis). Serotonergic system changes with aging include decreased serotonin receptor density, reduced tryptophan hydroxylase activity, and increased MAO-B activity (faster serotonin breakdown). Late-life depression is a significant risk factor for dementia: LLD doubles the risk of Alzheimer disease and may represent a prodromal phase of neurodegeneration in some patients. The concept of 'depression-executive dysfunction syndrome' describes LLD associated with frontal lobe dysfunction - these patients have prominent apathy, psychomotor retardation, poor response to antidepressants, and high relapse rates. LLD is associated with increased mortality from suicide (elderly white males have the highest suicide rate of any demographic), cardiovascular disease (depression is an independent cardiac risk factor through HPA axis activation, platelet hyperreactivity, and autonomic dysfunction), and functional decline.