A new study sheds light on the neurologic underpinnings of late-life depression (LLD) with apathy and its frequently poor response to treatment.
Investigators headed by Faith Gunning, PhD, of the Institute of Geriatric Psychiatry, Weill Cornell Medicine, New York, analyzed baseline and posttreatment brain MRIs and functional MRIs (fMRIs) of older adults with depression who participated in a 12-week open-label nonrandomized clinical trial of escitalopram. Participants had undergone clinical and cognitive assessments.
Disturbances were found in resting state functional connectivity (rsFC) between the salience network (SN) and other large-scale networks that support goal-directed behavior, especially in patients with depression who also had features of apathy.
“This study suggests that, among older adults with depression, distinct network abnormalities may be associated with apathy and poor response to first-line pharmacotherapy and may serve as promising targets for novel interventions,” the investigators write.
The study was published online in JAMA Network Open.
A leading cause of disability
LLD is a “leading cause of disability and medical morbidity in older adulthood,” with one-third to one-half of patients with LLD also suffering from apathy, the authors write.
Older adults with depression and comorbid apathy have poorer outcomes, including lower remission rates and poorer response to first-line antidepressants, compared with those with LLD but who do not have apathy.
Despite the high prevalence of apathy in people with depression, “little is known about its optimal treatment and, more broadly, about the brain-based mechanisms of apathy,” the authors note.
An “emerging hypothesis” points to the role of a compromised SN and its large-scale connections between apathy and poor treatment response in LLD.
The SN (which includes the insula and the dorsal anterior cingulate cortex) “attributes motivational value to a stimulus” and “dynamically coordinates the activity of other large-scale networks, including the executive control network and default mode network (DMN).”
Preliminary studies of apathy in patients with depression report reduced volume in structures of the SN and suggest disruption in functional connectivity among the SN, DMN, and the executive control network; but the mechanisms linking apathy to poor antidepressant response in LLD “are not well understood.”
“Connectometry” is a “novel approach to diffusion MRI analysis that quantifies the local connectome of white matter pathways.” It has been used along with resting-state imagery, but it had not been used in studying apathy.
The researchers investigated the functional connectivity of the SN, hypothesizing that alterations in connectivity among key nodes of the SN and other core circuits that modulate goal-directed behavior (DMN and the executive control network) were implicated in individuals with depression and apathy.
They applied connectometry to “identify pathway-level disruptions in structural connectivity,” hypothesizing that compromise of frontoparietal and frontolimbic pathways would be associated with apathy in patients with LLD.
They also wanted to know whether apathy-related network abnormalities were associated with antidepressant response after 12 weeks of pharmacotherapy with the selective serotonin reuptake inhibitor escitalopram.
Emerging model
The study included 40 older adults (65% women; mean [SD] age, 70.0 [6.6] years) with DSM-IV–diagnosis major depressive disorder (without psychotic features) who were from a single-group, open-label escitalopram treatment trial.
The Hamilton-Depression (HAM-D) scale was used to assess depression, while the Apathy Evaluation Scale was used to assess apathy. On the Apathy Evaluation Scale, a score of greater than 40.5 represents “clinically significant apathy.” Participants completed these tests at baseline and after 12 weeks of escitalopram treatment.
They also completed a battery of neuropsychological tests to assess cognition and underwent MRI imaging. fMRI was used to map group differences in rsFC of the SN, and diffusion connectometry was used to “evaluate pathway-level disruptions in structural connectivity.”
Of the participants, 20 had clinically significant apathy. There were no differences in age, sex, educational level, or the severity of depression at baseline between those who did and those who did not have apathy.
Compared with participants with depression but not apathy, those with depression and comorbid apathy had lower rsFC of salience network seeds (specifically, the dorsolateral prefrontal cortex [DLPFC], premotor cortex, midcingulate cortex, and paracentral lobule).
They also had greater rsFC in the lateral temporal cortex and temporal pole (z > 2.7; Bonferroni-corrected threshold of P < .0125).
Additionally, participants with apathy had lower structural connectivity in the splenium, cingulum, and fronto-occipital fasciculus, compared with those without apathy (t > 2.5; false discovery rate–corrected P = .02).
Of the 27 participants who completed escitalopram treatment; 16 (59%) achieved remission (defined as an HAM-D score <10). Participants with apathy had poorer response to escitalopram treatment.
Lower insula-DLPFC/midcingulate cortex rsFC was associated with less improvement in depressive symptoms (HAM-D percentage change, beta [df] = .588 [26]; P = .001) as well as a greater likelihood that the participant would not achieve remission after treatment (odds ratio, 1.041; 95% confidence interval, 1.003-1.081; P = .04).
In regression models, lower insula-DLPFC/midcingulate cortex rsFC was found to be a mediator of the association between baseline apathy and persistence of depression.
The SN findings were also relevant to cognition. Lower dorsal anterior cingulate-DLPFC/paracentral rsFC was found to be associated with residual cognitive difficulties on measures of attention and executive function (beta [df] = .445 [26] and beta [df] = .384 [26], respectively; for each, P = .04).
“These findings support an emerging model of apathy, which proposes that apathy may arise from dysfunctional interactions among core networks (that is, SN, DMN, and executive control) that support motivated behavior,” the investigators write.
“This may cause a failure of network integration, leading to difficulties with salience processing, action planning, and behavioral initiation that manifests clinically as apathy,” they conclude.
One limitation they note was the lack of longitudinal follow-up after acute treatment and a “relatively limited neuropsychological battery.” Therefore, they could not “establish the persistence of treatment differences nor the specificity of cognitive associations.”
The investigators add that “novel interventions that modulate interactions among affected circuits may help to improve clinical outcomes in this distinct subgroup of older adults with depression, for whom few effective treatments exist.”
Commenting on the study, Helen Lavretsy, MD, professor of psychiatry in residence and director of the Late-Life Mood, Stress, and Wellness Research Program and the Integrative Psychiatry Clinic, Jane and Terry Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, said, the findings “can be used in future studies targeting apathy and the underlying neural mechanisms of brain connectivity.” Dr. Lavretsy was not involved with the study. The study was supported by grants from the National Institute of Mental Health. Dr. Gunning reported receiving grants from the National Institute of Mental Health during the conduct of the study and grants from Akili Interactive. The other authors’ disclosures are listed on the original article. Dr. Lavretsky reports no relevant financial relationships.
A version of this article first appeared on Medscape.com.