By Nitin K. Sethi, MD
Associate Professor of Neurology, Weill Cornell Medical College; Director, Weill Cornell Concussion and Brain Injury Center
Mild traumatic brain injuries (mTBIs) may lead to adverse cognitive and neuropsychiatric outcomes. The pathways that lead to adverse cognitive outcomes remain to be scientifically elucidated. A prospective cohort study of 656 participants enrolled in the Transforming Research and Clinical Knowledge in TBI (TRACK-TBI) study found that at one year, 13.5% of participants with mTBI had poor cognitive outcome compared to 4.5% of controls, highlighting the need for better understanding of the mechanisms leading to poor cognitive and functional outcomes after mTBIs and interventions to optimize cognitive recovery.
Schneider ALC, Huie JR, Boscardin WJ, et al. Cognitive outcome 1 year after mild traumatic brain injury: Results from the TRACK-TBI study. Neurology 2022;98:e1248-e1261.
The authors in this prospective cohort study compared 656 participants 17 years of age or older (mean age 40.2 years, 36.6% female, 76.6% white) presenting to Level I trauma centers within 24 hours of mild traumatic brain injury (mTBI, defined as Glasgow Coma Scale score 13-15) with 156 demographically similar healthy controls enrolled in the Transforming Research and Clinical Knowledge in TBI (TRACK-TBI) study. All participants then were examined at two weeks, six months, and one year post-trauma and underwent a neuropsychological test battery of cognitive functions. This test battery consisted of five scores, capturing different aspects of cognitive function using three different tests. The Auditory Verbal Learning test looked at immediate and delayed recall, the Trail Making Tests A and B were administered for assessment of executive functioning, and the Processing Speed Index from the Wechsler Adult Intelligence scale also was administered.
A definition of cognitive impairment was determined by using demographically adjusted cutoffs. The investigators determined that the ninth percentile threshold would be the cutoff for cognitive impairment, consistent with other studies that were completed under the TRACK-TBI research program.
Poor one-year cognitive outcome was defined as cognitive impairment below the ninth percentile of normative data on two or more cognitive tests. Cognitive decline was defined as a change in score (one-year score minus best two-week or six-month score) exceeding the 90% reliable change index on two or more cognitive tests. Associations of poor one-year cognitive outcome with one-year neurobehavioral outcomes also were performed.
After comparison of baseline characteristics, logistic regression was used to build a prediction model. The cohort of mTBI participants with poor one-year cognitive outcome had worse one-year functional outcome, more neurobehavioral symptoms, greater psychological distress, and lower satisfaction with life.
At one-year follow-up, 13.5% of participants with mTBI had a poor cognitive outcome vs. 4.5% of control subjects (P = 0.003). Non-white race, lower education, lower income, lack of health insurance, hyperglycemia, preinjury depression, and greater injury severity correlated with poor one-year cognitive outcome. The authors, in their prediction model, found that education, health insurance, preinjury depression, hyperglycemia, and Rotterdam computed tomography score of 3 or higher were independently associated with more than twofold increased odds of poor one-year cognitive outcome.
COMMENTARY
There is no standardized definition of mTBI.1 In the absence of validated biofluid (blood/cerebrospinal fluid) and imaging biomarkers, separating concussion as a distinct pathophysiological entity from mTBI is not easy, leading to misconceptions and biases in the diagnostic process, uninterpretable science, poor clinical guidelines, and confused policy.
Currently mTBI is defined as a traumatically induced physiological disruption of brain function manifested by at least one of the following: any period of loss of consciousness, any retrograde or anterograde amnesia, any alteration in the level of consciousness, and focal neurological deficit(s) that may or may not be transient. Patients are classified as experiencing mTBI when loss of consciousness is approximately 30 minutes or less, they have an initial Glasgow Coma Scale (GCS) score of 13-15, and post-traumatic amnesia (PTA) does not exceed 24 hours.2
Historically, mTBI was used to describe patients briefly disabled following a head injury, with the assumption this was a transient disorder of brain function without long-term sequelae. Now it is well known that symptoms of mTBI are highly variable in duration and may persist for many years with no reliable early predictors of outcome.
In one study of 53 patients with mTBI, cognitive function was assessed at bedside within 24 hours post-injury. Compared to 28 healthy controls, mTBI patients exhibited significantly worse performance on Mini-Mental State Examination, Frontal Assessment Battery, naming, incidental memory, immediate memory, learning, and delayed recall. Patients with lower educational level had higher rates of cognitive impairment.
There was no difference in cognitive impairment between patients with or without loss of consciousness.3 It is likely that a significant number of patients with mTBI experience cognitive deficits acutely after the head impact exposure. In some of these patients, these deficits lead to long-term adverse cognitive and neuropsychiatric outcomes and poor quality of life.
Studies addressing factors that lead to adverse cognitive, neuropsychiatric, and functional outcomes after mTBI are needed. Evidence-based recommended practices then can be implemented early in patients with mTBI to prevent these adverse outcomes.
REFERENCES
- Ruff RM, Jurica P. In search of a unified definition for mild traumatic brain injury. Brain Inj 1999;13:943-952.
- Silverberg ND, Iverson GL; ACRM Mild TBI Definition Expert Consensus Group and the ACRM Brain Injury Special Interest Group Mild TBI Task Force. Expert panel survey to update the American Congress of Rehabilitation Medicine definition of mild traumatic brain injury. Arch Phys Med Rehabil 2021;102:76-86.
- de Freitas Cardoso MG, Faleiro RM, de Paula JJ, et al. Cognitive impairment following acute mild traumatic brain injury. Front Neurol 2019;10:198.
