Recent interdisciplinary consensus work ¹ identified areas of agreement and active dispute in mild TBI diagnosis. Agreement emerged around broadening the definition of observable signs to include subtle indicators such as blank or vacant appearance, delayed verbal responses, or transient motor incoordination—features often omitted from formal criteria yet recognized by experienced observers.

Disagreement persisted on several key points: whether acute symptoms alone suffice for diagnosis, whether minimum symptom duration should be mandated, and whether positive structural imaging can still be classified within the “mild” category. Sport concussion and non-sport civilian frameworks remain partially segregated, perpetuating inconsistent use of the terms mild TBI and concussion. ^{10, 11}

These definitional differences carry direct operational consequences for rural emergency medicine. Guidelines requiring direct observation of qualifying signs may miss cases entirely when initial evaluation occurs after sign resolution. In such settings, credible retrospective evidence—supported by mechanism, witness description, and symptom course—becomes essential for accurate classification. ¹²

The temporal parameters underlying our missed diagnostic window calculations derive from comprehensive systematic review evidence. Alruwaili and Alanazy ⁵ conducted the most recent systematic review of EMS response time differences between urban and rural areas, analyzing 37 studies (n = 239,464,121 total patients) published between 1991-2022. Twenty-nine studies (78.4%) reported statistically significant differences in response time between rural and urban areas, with remarkably variable reported response times reflecting true heterogeneity in EMS system performance.

An earlier systematic review ¹³ examined 31 studies and confirmed that EMS in urban areas consistently demonstrated shorter prehospital times, response times, on-scene times, and transport times compared to rural areas, with urban patients experiencing higher survival rates for both out-of-hospital cardiac arrest and trauma. These findings establish the robust evidence base for rural-urban EMS timing disparities that drive the observability gap in mTBI diagnosis.

Loss of Consciousness Duration: Meta-analysis of 31 empirical samples of concussed athletes ³ found that loss of consciousness duration data consistently showed median values under one minute across sports-related concussion studies. This finding aligns with earlier prospective studies documenting brief LOC durations in witnessed sport concussions.

Post-Traumatic Amnesia Evidence: The first comprehensive systematic review and meta-analysis of post-traumatic amnesia duration ¹⁴ analyzed 9 studies incorporating 12,386 patients. This meta-analysis revealed that PTA durations excluded moderate-to-severe disability outcomes with 87% sensitivity, while PTA durations of 43-86 days predicted disability with 90-96% specificity. However, the systematic review identified concerning variability in PTA assessment paradigms, with different measurement approaches recording substantially different PTA durations in identical patients.

Acute Confusion Resolution: Systematic review evidence from the International Collaboration on Mild Traumatic Brain Injury Prognosis ²⁴ found that cognitive deficits, including acute confusion states, typically resolved within the first few days to weeks post-injury in mild TBI, with most patients returning to normative cognitive performance levels within one month.

Quantifying the missed-diagnosis window: Probability model

To quantify the magnitude of diagnostic loss, we calculated probability distributions for missed signs based on published temporal data. The core mathematical relationship can be expressed as: P ( missed diagnosis ) = P ( T _ sign < T _ arrival )

Where: •

T_sign = duration of observable neurological signs

Empirical Probability Calculations using published distributions:

Sign Duration Medians: •

LOC: <1 minute ³

EMS Arrival Time Distributions ⁵ : •

Urban median: 15 minutes (IQR: 8-22 minutes)

Critical Finding: For rural systems with T_arrival >20 minutes: •

P (missed LOC) ≈ 0.95 (95% probability LOC unobserved)

Combined P (missed diagnosis) >0.70 when any qualifying sign would establish mTBI diagnosis.

This represents a systematic 70% underdiagnosis rate in rural EMS systems for cases where qualifying signs resolve before arrival profound public health and clinical equity issue.

When the decay curve of observable signs is overlaid against EMS arrival distributions, the mismatch becomes evident: the probability of observing qualifying signs falls sharply as time to assessment increases. In urban contexts, a meaningful proportion of cases remain within the observation window; in rural settings, that proportion drops substantially ¹⁵ ( Figure 1).

[Overlap of acute sign durations with EMS arrival times (Urban vs Rural)]

The Glasgow Coma Scale (GCS), developed for triage of severe head injury in neurosurgical and intensive care settings, has long been embedded in prehospital and emergency documentation. In mild TBI, however, GCS scores frequently reach ceiling (15/15) despite the presence of brief post-traumatic amnesia, altered mental status, or both. ¹⁶ These transient deficits, especially when unobserved, can be entirely absent from GCS scoring. Exclusive reliance on GCS for classification risks systematic underestimation of mTBI incidence. This limitation is magnified in delayed evaluations—common in rural EMS—where transient neurological signs have already resolved before initial scoring. In such scenarios, GCS may serve as a crude severity screen but cannot substitute for structured injury history, symptom inventory, and collateral corroboration ( Table 1).

When the initial observation window is missed, the adjudication process should branch according to whether the event was witnessed and incorporate time-to-assessment factors:

Witnessed Events: Brief observed loss of consciousness or altered mental status should be weighted heavily, even with delayed EMS arrival, as these signs often resolve within minutes (cf. 1,3,12).

Unwitnessed Events: Classification requires corroborative evidence such as mechanism specifics, third party descriptions, or contemporaneous communications, combined with exclusion of alternative causes (e.g., intoxication, syncope). ^{5, 12, 15}

Neurocognitive Testing as Tertiary Arbiter: When classification remains uncertain after structured history and guideline comparison, brief, targeted neurocognitive testing can assist. The objective is not a comprehensive battery, but selected measures with demonstrated discriminant validity for distinguishing mTBI from psychiatric or functional presentations. ^{17, 18} Testing should be norm-referenced, interpreted within context of history and observed behavior, and scored using appropriate demographic adjustments ( Table 2).

The following case demonstrates practical application of the time-adjusted adjudication framework in a rural EMS setting where traditional diagnostic approaches would likely miss the mTBI diagnosis.

Case: A 45-year-old ranch worker fell from a horse while checking cattle on remote grazing land in rural Montana. The nearest neighbor, alerted by the riderless horse returning to the barn, found the patient sitting upright but appearing “confused and not quite right” approximately 10 minutes post-incident. The patient could not recall the fall but remembered saddling the horse earlier that morning. By the time EMS arrived 32 minutes post-injury, the patient appeared alert and oriented with a GCS of 15/15, denied loss of consciousness, and complained only of mild headache and neck soreness.

Traditional Assessment: Standard emergency protocols would classify this as “no significant head injury” based on normal GCS, patient denial of LOC, and absence of observed neurological signs at the time of evaluation.

Time-Adjusted Adjudication Applied: 1.

Temporal Analysis: EMS arrival at 32 minutes exceeded the median duration for brief LOC (<1 minute) and acute confusion (~5 minutes), placing this case within the high-probability missed-sign window.

Outcome: Using the time-adjusted framework, this case met criteria for probable mTBI despite normal examination at EMS arrival. The patient received appropriate concussion education, activity restrictions, and follow-up instructions that would have been omitted under traditional assessment protocols. At 48-hour follow-up, the patient reported persistent headache, difficulty concentrating, and fatigue—symptoms consistent with post-concussive syndrome that supported the initial diagnosis.

Framework Impact: This case illustrates how temporal considerations and structured retrospective evidence can enable accurate mTBI diagnosis even when qualifying signs resolve before professional evaluation, particularly critical in rural settings where transport delays are common and specialist consultation is limited.

Systems Perspective: The Three Delays Model.

Adapting the well-established “three delays” model from maternal mortality research clarifies timing’s role in mTBI diagnosis. ¹⁹ In this adaptation: 1.

Injury → help-seeking (reporting lag): The interval between injury and the decision or ability to summon help. In mTBI, this can be prolonged by lack of symptom awareness, absence of witnesses, or competing priorities at the scene.

In severe TBI, third delays have been associated with mortality risk. ²⁰ In mTBI, these delays reduce the likelihood of observing qualifying signs during the acute period, reinforcing the need for retrospective adjudication when the observation window is missed. This framework emphasizes that all three delays contribute to the missed diagnostic window, with rural and resource-limited systems experiencing disproportionately longer second and third delays.

Telehealth integration represents a key accelerant in addressing this missed diagnostic window. Real-time video consultation during EMS response can document signs within minutes of injury, even before transport commences. ^{21, 22} This reduces dependence on memory-based collateral reports and preserves observation within the critical diagnostic window. Early capture of brief signs like LOC, altered mental status, or incoordination makes classification less vulnerable to the biases inherent in retrospective chart review.

Recent advances in EMS telehealth protocols ^{21, 22} further narrow the potential for underdiagnosis, allowing timely expert observation in the field and capturing signs before they resolve. The framework requires no additional technology beyond existing telemedicine platforms, making implementation feasible across diverse health systems.

The proposed time-adjusted adjudication framework addresses the critical missed diagnostic window in current diagnostic approaches, particularly for rural emergency medicine practitioners. The framework acknowledges temporal realities of emergency medical response, provides structured retrospective diagnosis that maintains scientific rigor while expanding diagnostic sensitivity, and offers telehealth integration that can reduce the missed diagnostic window without requiring wholesale system redesign.

Emergency physicians can use this framework to systematically evaluate delayed presentation mTBI cases, reducing diagnostic uncertainty and improving documentation for medicolegal purposes. EMS systems can integrate telehealth consultation during transport to capture transient signs that would otherwise be missed, improving diagnostic yield without additional equipment costs. This approach directly addresses the practice gap where qualifying neurological signs resolve before evaluation, leading to systematic underdiagnosis and potential denial of appropriate care, rehabilitation services, and disability benefits.

The framework’s standardized approach to retrospective evidence evaluation reduces inter-provider variability in mTBI diagnosis, particularly valuable in rural areas where specialists may be unavailable for consultation. Implementation requires only a shift in emphasis within existing protocols—not technological overhaul—making adoption feasible across resource-constrained settings.

This framework relies on published data regarding sign durations and EMS response times, which may vary across regions and systems. As a next step, we plan to examine these questions with de-identified NEMSIS data in partnership with EMS data scientists to evaluate generalizability and implementation feasibility.

The integration of emerging biomarkers and advanced neuroimaging techniques may further enhance diagnostic accuracy, particularly in cases where traditional clinical signs are equivocal. However, such technologies should complement rather than replace the fundamental temporal considerations outlined in this framework.