The spectrum of mild traumatic brain injury: A review

Abstract

Objective: This review provides an in-depth overview of diagnostic schema and risk factors influencing recovery during the acute, subacute (operationally defined as up to 3 months postinjury), and chronic injury phases across the full spectrum of individuals (e.g., athletes to neurosurgery patients) with mild traumatic brain injury (mTBI). Particular emphasis is placed on the complex differential diagnoses for patients with prolonged postconcussive symptoms.

Methods: Select literature review and synthesis.

Results: In spite of an increase in public awareness surrounding the acute and potential long-term effects of mTBI, the medical field remains fragmented both in terms of the diagnostic (different criteria proffered by multiple medical organizations) and prognostic factors that influence patient care.

Conclusions: Given the lack of objective biomarkers and the spectrum of different disorders that likely encompass mTBI, clinicians are encouraged to adopt a probabilistic, rather than definitive, diagnostic and prognostic framework. The relevance of accurately diagnosing and managing the different manifestations of mTBI becomes clear when one considers the overall incidence of the disorder (42 million people each year worldwide), and the different treatment implications for patients with a true neurodegenerative disorder (e.g., chronic traumatic encephalopathy; rare) vs potentially treatable conditions (e.g., depression or posttraumatic headache; frequent).

Figure 1. Current diagnostic nosology for mild traumatic brain injury (mTBI)

In spite of its confusing nature, figure 1 accurately depicts current diagnostic conceptualizations of mTBI across the continuum of care. According to some official diagnostic conceptualizations for acute mTBI (panel A and table), concussion (Cnc; cyan) represents the least severe form of recognized injury, and is necessary but not sufficient for all other diagnoses (i.e., all other diagnoses fall within the sphere of concussion). Single mTBI (smTBI; green) therefore represents a subset of concussion, although currently there are no clinical or diagnostic criteria proffered for distinguishing smTBI from concussion. A head injury associated with a positive imaging finding constitutes complicated mTBI (cmTBI; red, orange, and purple). Repetitive head injury (RHI) can occur in any of these diagnostic categories or across injury types (yellow, orange, and blue). Subconcussive blows and associated exposure history (Cnc_sub) are speculative and not officially recognized by any organizational body (represented with dashed rather than solid lines). (B) The superimposition of chronic conditions, operationally defined here as greater than 3 months postinjury, on acute diagnoses. Prolonged postconcussive symptoms (PPCS) can potentially span all acute diagnostic entities, and are currently diagnosed as major or mild neurocognitive disorder due to traumatic brain injury per the DSM-V. Although the prevalence of probable chronic traumatic encephalopathy (pCTE; clinical diagnosis) following a smTBI remains an active area of debate, it is included for thoroughness.

Figure 2. Ideal diagnostic nosology for mild traumatic brain injury (mTBI)

In contrast to figure 1, figure 2 depicts a set of linear diagnostic entities that represent the full spectrum of mTBI across both acute and chronic phases. The adopted color scheme is similar to figure 1 for single head injury (subconcussive blows [Cnc_sub]; concussion [Cnc] = cyan to blue; single mTBI [smTBI] = green to yellow; complicated mTBI [cmTBI] = orange to purple) as well as repetitive head injury (yellow, orange, and blue within each category). In this idealized system, each of the individually proposed entities is diagnostically distinct (denoted by the separating white space between entities) rather than conflated (as indicated by overlapping circles in figure 1). Each entity would ideally be defined by a specific and objective in-life biomarker or independent measurement (represented by multicolored vertical arrows), which currently only exists for cmTBI. Existing evidence for in vivo biomarkers is denoted by Y for yes, S for some, or N for none. pCTE = probable chronic traumatic encephalopathy; PPCS = prolonged postconcussive symptoms.

Figure 3. Differential diagnosis and management strategy for prolonged postconcussive symptoms (PPCS)

Multiple etiologies may contribute simultaneously to PPCS; testing for these should proceed in parallel, as should multimodal treatment. Long-term monitoring for evidence of transition from PPCS to other neurodegenerative disorders in high-risk individuals (i.e., patients with multiple head injuries) is recommended following appropriate treatments. TBI = traumatic brain injury.