Identifying which biomarkers precede treatment-resistant depression in older adults matters because biological signals can guide earlier, more targeted interventions. Clinical features such as prolonged course and executive dysfunction remain central, but converging evidence points to neuroimaging, inflammatory, neuroendocrine, and neurodegenerative markers as predictors of poor antidepressant response.
Neuroimaging and vascular markers
Imaging studies led by George S. Alexopoulos at Weill Cornell Medicine emphasize the role of white matter hyperintensities and microvascular brain injury in late-life depression. These lesions on MRI are associated with poorer remission rates following standard antidepressant treatment, supporting a vascular depression pathway. Reduced hippocampal volume on structural MRI, linked to chronic stress and aging, also correlates with lower treatment responsiveness, a relationship described in the broader stress-neurobiology work of Bruce McEwen at Rockefeller University.
Inflammation, neurotrophic factors, and HPA-axis
Elevated peripheral inflammatory markers such as C-reactive protein and interleukin-6 have been associated with treatment nonresponse in older adults; investigators including Helen Lavretsky at the University of California Los Angeles report that higher systemic inflammation often accompanies poorer clinical outcomes. Lower levels of the neurotrophic factor BDNF and dysregulation of the hypothalamic–pituitary–adrenal axis, manifesting as altered cortisol patterns, further predict resistance to conventional antidepressants, reflecting impaired neural resilience and plasticity.
Amyloid and neurodegenerative pathology are increasingly studied as contributors to antidepressant failure. Work by Reisa A. Sperling at Brigham and Women’s Hospital, Harvard Medical School examines how amyloid and tau burden measured with PET imaging can coincide with depressive symptoms and cognitive decline, suggesting that underlying neurodegeneration may undercut antidepressant effects in some older adults.
Biological predictors do not act in isolation. Social isolation, chronic medical illnesses, cardiovascular risk factors, and disparities in access to diagnostic imaging or specialty care shape both biomarker prevalence and clinical outcomes. Populations with higher vascular risk are more likely to show imaging and inflammatory signatures that forecast poor response.
Recognizing these biomarkers has practical consequences: integrating vascular risk reduction, anti-inflammatory strategies, cognitive rehabilitation, or trials of alternative pharmacologic mechanisms can be prioritized when such signals are present. A multimodal assessment combining clinical phenotype, cognitive testing, blood biomarkers, and selective imaging offers the most evidence-based route to identify older adults at risk of treatment-resistant depression and to tailor interventions accordingly.