Level of Cognitive Impairment Tied to TBI Severity After Six Months

Patients with traumatic brain injury (TBI) can present with diverse phenotypes of cognitive impairment at 6 months post-injury. However, many patients with a history of milder TBI present similarly to uninjured individuals at 6 months. These are the findings of a large cohort study published in JAMA.

For the study, researchers collected data from the Transforming Research and Clinical Knowledge in TBI (TRACK-TBI) study, a prospective cohort from 18 US level 1 trauma centers. The researchers included 1057 patients (mean age, 39; 33% female; 77% White). These patients had presented between March, 2014, and July, 2018, within 24 hours of head injury, with previous history or findings warranting head computed tomography (CT) imaging.

The research team compared these participants to a control group of 327 people, composed of individuals with orthopedic injuries, and healthy family members and friends, without TBI. Cognitive assessment tests for all participants measured verbal episodic memory, processing speed, and executive functioning.

To estimate the preinjury cognitive capacity of the TBI group, the researchers assessed crystallized intelligence via the National Institutes of Health Toolbox Picture Vocabulary Test, as this measure is relatively unaffected by injury. Cognitive impairment was defined by comparison with the control group’s performance; cognitive decline was measured against the TBI group’s own vocabulary test scores. Furthermore, rather than simply compare the injured patients with the unaffected group, the researchers compared subgroups among these patients with TBI, to differentiate several distinct phenotypes of cognitive functioning.

The results broadly confirmed a severity-dependent effect of injury on cognitive dysfunction. Across subgroups, between 6.2% (95% CI, 2.4%–12.7%) and 32.7% (95% CI, 23.9%–42.4%) of patients with moderate-to-severe TBI (ie, with GCS scores between 3 and 12) had cognitive impairment at 6 months. By contrast, between 6.2% (95% CI, 3.8%–9.5%) and 15.3% (95% CI, 11.5%–19.8%) of those with CT-positive mild TBI demonstrated cognitive impairment.

Participants who had milder TBI (ie, who had Glasgow Coma Scale [GCS] scores between 13 and 15 on admission), and whose CT studies showed signs of acute injury, displayed similar cognitive function at 6 months postinjury to those with unremarkable CT studies.

Processing speed and memory were affected more often than executive function, among those with moderate-to-severe injury. However, patients who were cognitively impaired demonstrated a heterogeneous array of cognitive loss phenotypes, displaying such discrete losses either in isolation or in combination.

Cognitive decline, as measured against vocabulary test scores, was less prevalent than impairment, but followed similar patterns to those for impairment. Global cognitive decline (beyond 1.5 standard deviations of estimated preinjury function in all domains) was rare, peaking at a prevalence of 2.4% in the moderate-to-severe TBI group.

A study limitation was that it only included patients with injury sufficient to warrant head CT imaging, which could limit generalizability to a broader patient population.

“Future studies should investigate factors that predict distinct cognitive profiles and how cognitive rehabilitation or interventions can be tailored to patients’ cognitive strengths and weaknesses.”

Disclosures: Several study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see original source for full list of disclosures.