Analyzing the Spectrum of mTBI Subgroups.

Patients who sustain a mild traumatic brain injury (mTBI) experience a variety of clinical trajectories. Recent efforts to identify mTBI subtypes have begun to describe observed phenotypic variability. Clinical applicability of these subtypes is limited due to critical variations in each subtype's defining characteristics and limited inclusion of objective data. Here, we review mTBI literature that describes subtypes at various timepoints following injury. We describe five predominately symptom-based subtypes (cognitive, somatosensory, vestibular-ocular, headache, and neuropsychiatric [affective/behavioral]). Each of these subgroups has been reported at separate timepoints postinjury, with the majority of studies describing symptom clusters in the acute and subacute recovery period. Analysis of each subgroup indicates significant overlap and ambiguity within the currently described symptom-based subtypes of mTBI. Additionally, inconsistent terminology within symptom description and subtyping nomenclature limit the ability to compare among one another. We suggest that improved understanding of possible biological processes that contribute to certain clinical trajectories may be identified by incorporating objective assessments, biomarkers, neuroimaging, and genetic analysis into future mTBI subtyping analysis. In doing so, advancements toward individualized symptom management, recovery, and improved care for our mTBI community are possible.