Research Analyzes the Role of Glutamate in Traumatic Brain Injury Patient Outcome

Newswise — Close to 1.5 million cases of traumatic brain injury (TBI) occur in the United States every year. Approximately 5.3 million people live with a TBI-related disability and an additional 60,000 people die annually from TBI. Brain injury is the ultimate cause of death in 40 percent of all fatal trauma cases. Head trauma remains the leading cause of death and severe disability in young adults.

A TBI is defined as a blow to the head or a penetrating head injury that disrupts the normal function of the brain. TBI can result when the head suddenly and violently hits an object, or when an object pierces the skull and enters brain tissue. Symptoms of a TBI can be mild, moderate, or severe, depending on the extent of damage to the brain. Mild cases may result in a brief change in mental state or consciousness, while severe cases may result in extended periods of unconsciousness, coma, permanent disabilities, or death. "Unveiling the molecular basis of TBI is crucial for a better understanding of this condition, potentially leading to an improvement in the treatment and outcome of these patients," stated Roukoz B. Chamoun, MD, lead author.

Researchers at Baylor College of Medicine, Ben Taub General Hospital, Houston, investigated the role of glutamate, an excitatory amino acid, in the pathophysiology of TBI. The results of this study, The Role of Extracellular Glutamate Measured by Cerebral Microdialysis in Severe Traumatic Brain Injury, will be presented by Dr. Chamoun, 2:45 to 2:59 pm, Monday, May 4, 2009, during the 77th Annual Meeting of the American Association of Neurological Surgeons in San Diego. Co-authors are Snankar Gopinath, MD, Claudia Robertson, MD, and Dima Suki, PhD.

Previous studies suggest that glutamate plays an important role in TBI. "The purpose of this study was to measure glutamate levels in cerebral microdialysis in patients with severe TBI and to analyze their prognostic value," stated Dr. Chamoun. A prospective study involving 165 patients with severe TBI was conducted. All patients had a total Glasgow Coma Score of 8 or less within 48 hours of the injury.

All patients suffered from severe TBI and were treated according to a standard protocol at Ben Taub General Hospital (a Level I Trauma Center). Management included surgery (when indicated), invasive monitoring including intracranial pressure (ICP) measurements and brain tissue oxygenation, demographic data, CT scan findings and 6-month follow-up outcomes. The following results were noted:

"¢Initial high glutamate values were found to be predictive of a poor outcome.

"¢The mortality rate was 30.3 percent (glutamate more than 20) versus 18 percent (glutamate less than 20).

"¢Multiple patterns of changes in glutamate levels over time were identified, and they had different prognostic values. Two general patterns were recognized; Pattern 1: glutamate levels tended to normalize over the monitoring period (120 hours); Pattern 2: glutamate levels tended to increase with time or remain abnormally elevated.

"¢Patients exhibiting pattern 1 had a lower mortality rate (17.1 percent versus 39.6 percent) and a better 6-month functional outcome among survivors (41.2 percent achieving good outcome versus 20.7 percent).

"Glutamate levels and patterns measured by microdialysis appear to have an important role in TBI. This data suggest that they are correlated with the mortality rate and 6-month functional outcome. The results of this research yielded several interesting clinical aspects which warrant additional studies," stated Dr. Chamoun. Future research could focus on the following:

"¢Utilizing substance measurements through cerebral microdialysis to influence therapeutic decisions and to potentially improve outcome.

"¢Developing treatment targeted to patients based on their specific glutamate pattern.

"¢Identifying subgroups based on glutamate levels or patterns of change over time.

"¢Using anti-glutamate therapy to benefit subgroups of patients.

"¢Introducing these treatment measures into routine clinical practice.

Founded in 1931 as the Harvey Cushing Society, the American Association of Neurological Surgeons (AANS) is a scientific and educational association with more than 7,400 members worldwide. The AANS is dedicated to advancing the specialty of neurological surgery in order to provide the highest quality of neurosurgical care to the public. All active members of the AANS are certified by the American Board of Neurological Surgery, the Royal College of Physicians and Surgeons (Neurosurgery) of Canada or the Mexican Council of Neurological Surgery, AC. Neurological surgery is the medical specialty concerned with the prevention, diagnosis, treatment and rehabilitation of disorders that affect the entire nervous system, including the spinal column, spinal cord, brain and peripheral nerves.

Funding for this research was provided by the National Institutes of Health (NIH). The author reports no conflicts of interest.

Media Representatives: If you would like to cover the meeting or interview a neurosurgeon " either on-site or via telephone " please contact the AANS Communications Department at (847) 378-0517 or call the Annual Meeting Press Room beginning Monday, May 4 at (619) 525-6252.