Key Points: Although traumatic brain injuries involve brain-related symptoms, other organs including the immune system, GI system, lungs, and heart may also be compromised. These injuries can result in changes throughout the body that can increase morbidity and even mortality.
Traumatic brain injury (TBI) results from a head injury that damages the brain. Symptoms can include loss of consciousness, post-traumatic amnesia, memory loss, disorientation, and confusion. Symptoms occur immediately following the brain trauma and last for a while afterward. Psychiatric symptoms also may occur and include mood fluctuations, depression, anxiety, irritability, and personality changes. Other CNS (central nervous system) symptoms such as dizziness, headache, tinnitus, light sensitivity, and decreased sense of smell can also occur.
In an interesting paper recently published in Trends in Neurosciences, Alan Faden and colleagues discuss the consequences of TBI that involve organ systems other than the brain. They review evidence demonstrating that TBI can lead to significant changes in the immune, gastrointestinal (GI), pulmonary, and cardiovascular systems. These changes have been observed in humans and are being studied in animal models of TBI.
TBI is associated with a high rate of infections. It causes complex changes in the immune system, both systemically and in the brain. The result of these changes is the suppression of immune responses. These changes can persist over time, become chronic, and contribute to increased mortality.
Changes in the GI tract resulting in it being more permeable to substances and, therefore, less able to block the entry of toxins or bacteria into the circulation. The GI system also becomes more susceptible to infections as well as to relapse from ongoing, chronic GI disorders. Changes in the bacteria inhabiting the GI system (the gut microbiome) also occur. As discussed in an earlier post, the gut microbiome system communicates with the brain and influences brain function.
Lung damage is common following TBI. Individuals are susceptible to respiratory infections that can lead to pneumonia. Inflammatory chemicals are released into the lungs. Some of these changes result from TBI-related changes in the immune system.
Levels of certain chemicals in the blood indicate that cardiac damage may occur following TBI. Animal studies also suggest that TBI can lead to diminished cardiac function.
How do traumatic injuries to the brain lead to dysfunction in other organs? The authors review several possibilities. Following TBI, there are changes in the hypothalamic-pituitary-adrenal (HPA) system that lead to alterations in cortisol production. Such changes can interfere with the body’s ability to respond to stressors. TBI also can lead to a surge in activity of the sympathetic nervous system, which involves catecholamines such as norepinephrine. Such a surge can influence the function of various organs. As already mentioned, TBI results in changes in the immune system throughout the body, which can contribute to chronic neuroinflammation and neurodegeneration.
The take-home message is that TBI can result in changes throughout the body that can increase morbidity and even mortality. Increased understanding of these changes will hopefully lead to better treatments to prevent these deleterious consequences of TBI.
This review article by Faden and colleagues reminds all of us of the intimate relationships between brain function and the function of other organs in the body, and that successful treatment of brain diseases can have widespread positive impact on human physiology.
This column was written by Eugene Rubin MD, Ph.D., and Charles Zorumski MD.
Faden, A.I., Barrett, J.P., Stoica, B.A., & Henry, R.J. (2021 Jan 22). Bidirectional brain-systemic interactions and outcomes after TBI. Trends Neurosci. S0166-2236(21)00002-3. doi: 10.1016/j.tins.2020.12.004. [online ahead of print].