TBI

Combat PTSD/TBI Increases Amygdala Size in Military Patients

by U.S. Medicine

September 22, 2019

SAN DIEGO—The region of the brain that processes fear, anxiety, aggression and similar emotions is larger in veterans and active-duty service members with combat-related post-traumatic stress disorder and mild traumatic brain injury than those with brain injuries only.

That’s according to an article appearing online in the Journal of Head Trauma Rehabilitation.1

VA San Diego Health Care System-led researchers used magnetic resonance imaging to determine that the right and left sides of the amygdala in people with combat-related PTSD and mild traumatic brain injury (mTBI) were expanded in patients with only combat-related mTBI.

Included in the study were 89 veterans and active-duty military personnel, about one-third of whom had both PTSD and mTBI, with the remainder in the mild-TBI-only control group.

“This is an intriguing structural finding, given the role of the amygdala in the challenging [neuropsychological] symptoms witnessed in casualties of combat-related mTBI and PTSD,” the researchers write. “Further investigation is needed to determine whether amygdala size could be used to screen people at risk for PTSD, or whether it could be used to monitor the [effectiveness of medical solutions].”

Lead researcher Mingxiong Huang, PhD, a neuroimaging scientist at the San Diego VAMC and the University of California San Diego Health Care System said he and his colleagues were surprised by the discovery of a larger amygdala in veterans with combat-related PTSD and mTBI.

“Some previous PTSD research showed declines in amygdala volume based on the assumption of a loss of size due to injuries,” Huang said. “Our finding of increased amygdala volume seems to point to different mechanisms, such as an exposure to repetitive fear and stress.”

Co-author Douglas Chang, MD, PhD, of the VA San Diego, explained, “The amygdala is involved with processing threat perception and arousal and with linking emotion to experience in complex ways. A larger amygdala volume may be a sign of hyperactivity with an enlarged neural network. But we don’t know whether this is an attempt by the brain to cope with PTSD or whether the growth and enlargement is causing symptoms, like an electrical storm.”

The finding raised some interesting questions, Chang pointed out, asking, “The situation may also resemble scar tissue formation on skin. Is this an organized response by the body to heal itself, or is the scar tissue going haywire and forming a grossly disfigured area? Another possibility is that this study simply identified at-risk people for PTSD with a pre-existing condition: an enlarged amygdala.”

The testing was conducted at VA San Diego and at two Marine Corps bases in California. Researchers measured intracranial volume, a key statistic used to analyze the size of the brain and brain regions, especially in cases of neurodegenerative diseases.

The size of the right amygdala was 0.122%of total brain volume, on average, in the group with mTBI and PTSD. It was 0.115% in the cohort with only mTBI. The size of the left amygdala was 0.118% of brain volume in those with mTBI and PTSD, compared with 0.112% in the mTBI group. The researchers found both of those differences to be “statistically significant.”

“To be able to see a structural difference between these two cohorts and in this stage of PTSD really points to something going on with the amygdala,” Chang says. “Can we use this as a screening tool to identify people at risk? Maybe this is an adaptive response that we can monitor and use to track different kinds of mental health treatment approaches. Maybe yoga is helpful, maybe mindfulness meditation is helpful, maybe exercise is helpful. Perhaps there are drugs that can protect somebody against these traumas or to help improve their conditions. To be able to identify something that’s changed in a quantitative way is amazing. It opens the door to many possibilities to help treat this problem.”

  1. Pieper J, Chang DG, Mahasin SZ, Swan AR, et. Al. Brain Amygdala Volume Increases in Veterans and Active-Duty Military Personnel With Combat-Related Posttraumatic Stress Disorder and Mild Traumatic Brain Injury. J Head Trauma Rehabil. 2019 Apr 25. doi: 10.1097/HTR.0000000000000492. [Epub ahead of print] PubMed PMID: 31033749.


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