In a recent previous post the topic was the neuroanatomy of depression, or which sites of the brain can play a role in depression. Which parts of the brain show the dysfunction underlying depression. MRI scans can link neurobiology of depression with clinical findings through brain imaging studies that examine regional structure, regional function or connectivity. This can aid the diagnosis of depression. But can structural and functional MRI predict response to an antidepressant or psychotherapy?
From a recent review including studies examining the relations between imaging and clinical outcome in patients with depression:
In general, patients who remit have larger pretreatment hippocampus volumes bilaterally compared with those who do not remit.
One of the major drawbacks of these kind of studies is the lack of proof of causality. Even in longitudinal studies, the imaging during the course of the illness always starts when the patient is depressed. Besides this influence on the results of imaging studies other factors can also influence the measures. These studies can generate hypotheses about the prediction of response to treatments not causality. The difference between longitudinal and cross sectional studies is best explained by the following example:
the observed correlation between London taxi-driving and hippocampus volume in cross-sectional studies that led to the suggestion that driving around London, England, resulted in larger regional brain volumes. An alternative explanation, testable with a longitudinal approach, is that drivers with larger hippocampus volumes become successful and remain on the job longer than those with small hippocampus volumes and minimal propensity for spatial navigation. Longitudinal imaging studies are also more powerful for studies that have the goal of developing biomarkers that are relevant for early detection of disease, prediction of disease progression or development of treatment strategies
Patients with depression have hippocampus volumes that are about 5%–8% smaller than healthy controls. Moreover, small hippocampus volumes are associated with depression severity, age at onset, nonresponsiveness to treatment, untreated days of illness, illness burden, history of childhood abuse, level of anxiety and certain genetic polymorphisms. Other neuropsychiatric conditions such as psychotic disorder, dementia, PTSD are also associated with a small hippocampus. It’s still unclear whether these conditions have a common pathway affecting the hippocampus or each condition has it’s own mechanism influencing the size of the hippocampus.
Most structural studies with MRI have focused on the hippocampus and outcome of depression treatment. Other structures of interest such as the prefrontal cortex, anterior cingulate cortex were also reported to have brain volume changes and response to treatment.
Using functional MRI
Studies using functional instead of a structural approach are preliminary and difficult to compare. These studies have showed that those responding have different activity patterns in the brain than those who don’t respond.
MacQueen GM (2009). Magnetic resonance imaging and prediction of outcome in patients with major depressive disorder. Journal of psychiatry & neuroscience : JPN, 34 (5), 343-9 PMID: 19721844