This discussion examines and contrasts two distinct methodologies for classifying traumatic brain injuries: the American Congress of Rehabilitation Medicine (ACRM) Diagnostic Criteria for mild TBI and the Mayo Classification System for TBI Severity. It is based on an article of Dr Ioannis Mavroudis, which analyses the strengths, limitations, and diagnostic accuracy of each system, noting the ACRM’s comprehensive and adaptable nature alongside the Mayo system’s established simplicity. The article also proposes a hybrid diagnostic algorithm that integrates elements from both frameworks to improve mTBI identification across varied clinical contexts. Ultimately, the piece concludes that while both systems offer value, the ACRM criteria provide greater accuracy for mTBI, though resource limitations could affect its universal implementation.
Welcome to Beyond the Impact. I’m Dr. Ioannis Mavroudis, consultant neurologist, researcher, and clinician with a deep commitment to understanding and improving the diagnosis of traumatic brain injuries. In today’s episode, we’re diving into an in-depth discussion of two of the most widely referenced diagnostic frameworks for mild traumatic brain injury: the American Congress of Rehabilitation Medicine—or ACRM—Diagnostic Criteria, and the Mayo Classification System for TBI Severity.
Our goal is to compare these two systems, explore their strengths and limitations, understand how they’re applied in both clinical and research settings, and discuss what this means for improving patient care and diagnostic accuracy. If you’re a clinician, researcher, medicolegal professional, or someone passionate about brain health, this episode is for you.
Let’s begin with the challenge at the heart of this issue.
Traumatic brain injuries—and especially mild TBIs or concussions—are not easy to diagnose. While moderate to severe TBIs are usually evident with obvious signs, loss of consciousness, or visible brain lesions on imaging, mild TBIs are more elusive. They often lack definitive biomarkers, and the symptoms can be vague, delayed, and influenced by many factors. Yet the consequences of failing to identify and manage mTBI can be profound—ranging from persistent cognitive symptoms and psychological disturbances to long-term neurodegenerative changes.
Over the years, various diagnostic systems have been created in an attempt to standardize what we mean when we say “mild traumatic brain injury.” Two of the most established and widely used are the ACRM Diagnostic Criteria and the Mayo Classification System.
Let’s start with the ACRM.
The ACRM Diagnostic Criteria
The ACRM criteria are built around six foundational elements that reflect the complexity of mTBI. They are:
- Mechanism of Injury
- Clinical Signs
- Acute Symptoms
- Clinical and Laboratory Findings
- Neuroimaging
- Exclusion of Confounding Factors
Let’s take these one by one.
1. Mechanism of Injury
The ACRM framework begins by recognizing that mTBI can arise from a variety of biomechanical events. These include direct impacts to the head, acceleration-deceleration forces—such as those in whiplash injuries—and exposure to blast or explosion forces, especially in military settings.
The key here is plausibility. If there is a biomechanically plausible scenario—say, a soldier exposed to a blast wave or an athlete who took a sudden jolt to the neck—we have a foundation to consider mTBI, even in the absence of direct cranial trauma.
2. Clinical Signs
Next, we look for observable disruptions in brain function. This includes classic signs like loss of consciousness, confusion, post-traumatic amnesia, and acute neurological abnormalities such as unsteady gait or seizures.
The ACRM is precise about these definitions. Disorientation, for instance, isn’t just feeling “off.” It must be demonstrated—such as the patient being unable to state where they are or what time it is.
3. Acute Symptoms
To satisfy the ACRM criteria, the patient must experience at least two acute symptoms from a well-defined list. These include cognitive issues (like difficulty concentrating), physical symptoms (headache, nausea, dizziness), and emotional changes (like irritability or anxiety). Crucially, these symptoms must emerge within 72 hours of the injury to ensure a direct link.
4. Clinical and Laboratory Findings
Here, we integrate objective data from neurological exams, vestibular testing, cognitive screens, and increasingly, biomarkers. Blood tests that detect glial fibrillary acidic protein, for instance, are an exciting frontier. We also consider eye movement abnormalities and balance impairments.
5. Neuroimaging
Interestingly, imaging is optional in the ACRM system. If findings are present—say, a microhemorrhage or contusion—they add the qualifier “mTBI with neuroimaging evidence.” But if the scan is clean, we don’t rule out mTBI. This reflects the real-world truth: many concussions don’t show up on CT or even MRI.
6. Exclusion of Confounding Factors
Finally, we must rule out other causes for the symptoms. This includes psychiatric conditions like PTSD, intoxication, or pre-existing neurological issues. This component is vital—it ensures that we’re not labeling someone with mTBI when another diagnosis would be more accurate.
Innovations of the ACRM Criteria
Let’s talk about three unique contributions of this system.
First, probabilistic diagnosis. The ACRM allows for a “suspected mTBI” label in cases where full data isn’t available—such as delayed evaluations or complex presentations. This is invaluable in real-world practice, where patients don’t always come in right away or may have multiple concurrent injuries.
Second, the integration of biomarkers marks a shift toward precision neurology. While the research is still maturing, incorporating these into diagnostic workflows reflects where the field is headed.
Third, and importantly, the criteria are adaptable. They’re not limited to one setting—they can be used in sports medicine, military triage, emergency departments, and beyond. That versatility is crucial for improving diagnostic consistency across systems.
Strengths of the ACRM Criteria
So what are the core strengths?
- Comprehensiveness: It’s a 360-degree view—mechanism, symptoms, signs, imaging, labs, exclusions.
- Operational clarity: Each component is well defined, reducing ambiguity.
- Flexibility: It allows for nuance—imaging optional, probabilistic diagnosis allowed.
- Standardization: It’s excellent for research, allowing apples-to-apples comparison of studies.
Limitations of the ACRM
However, it’s not perfect.
- Resource intensive: Not every clinic has access to cognitive tests, vestibular exams, or biomarker assays.
- Complex: It can be daunting for clinicians unfamiliar with mTBI to apply it fully.
- Validation still ongoing: We need more data in diverse populations to confirm its predictive value.
The Mayo Classification System
Now let’s turn to the Mayo Classification System. This framework is designed primarily for research but is often used clinically.
It divides TBI into three categories:
- Definite TBI (Moderate-Severe)
- Probable TBI (Mild)
- Possible TBI (Symptomatic)
Definite TBI includes cases with clear evidence—GCS less than 13, PTA over 24 hours, or imaging findings.
Probable TBI includes GCS 13–15, LOC under 30 minutes, PTA under 24 hours, and post-concussive symptoms.
Possible TBI covers symptomatic individuals without clear evidence of trauma.
This hierarchy allows us to stratify severity and manage accordingly.
Strengths of the Mayo System
- Simplicity: It’s easy to apply and communicate.
- Evidence-based tiers: Built around objective findings.
- Widespread use: Especially in epidemiological and longitudinal studies.
Limitations of the Mayo System
- May under-identify subtle cases: Especially those with normal imaging and vague symptoms.
- Less granular than ACRM: It doesn’t integrate biomarkers or nuanced symptom analysis.
- Relies heavily on historical data: Which can be incomplete or unreliable in retrospective reviews.
Comparative Summary
If we compare the two side by side:
- ACRM: Comprehensive, flexible, forward-looking, but complex and resource-heavy.
- Mayo: Simple, structured, research-friendly, but less detailed and may miss edge cases.
They’re not mutually exclusive. In my practice, I often use both—starting with Mayo for classification and then applying ACRM criteria to determine diagnostic precision and plan interventions.
Clinical Implications
The diagnostic system we choose impacts:
- Patient care: Early diagnosis can mean timely therapy and better outcomes.
- Research quality: Standardized criteria improve study comparability.
- Medicolegal practice: Clear diagnostic rationale is critical in legal contexts.
- Policy: Drives investment in training, tools, and care pathways.
Conclusion
As our understanding of TBI evolves, so too must our diagnostic systems. The ACRM and Mayo frameworks each offer valuable tools, but we must apply them thoughtfully, critically, and adaptively. Emerging biomarkers, advanced imaging, and digital diagnostics will only enhance these systems moving forward.
Ultimately, the goal remains the same: to improve outcomes for individuals living with the invisible scars of brain injury. That journey starts with diagnosis—accurate, timely, and compassionate.
Thank you for joining me on Beyond the Impact. I’m Dr. Ioannis Mavroudis. Until next time, stay informed, stay curious, and continue advocating for evidence-based brain health.
