What are the diagnostic criteria for concussion in an adult or adolescent patient with a head injury?

Concussion Diagnostic Criteria

Concussion is diagnosed clinically when a patient presents with observed disorientation/confusion immediately after head trauma, impaired balance within 1 day, slower reaction time within 2 days, and/or impaired verbal learning and memory within 2 days after injury. 1

Core Definition

Concussion represents a functional disturbance rather than structural injury to the brain, with normal standard neuroimaging by definition. 2 The diagnosis requires:

• Transmission of mechanical energy through direct blow to the head, neck, or body causing brain dysfunction 1, 2
• Glasgow Coma Scale score of 13-15 2, 3
• Loss of consciousness less than 30 minutes (if present) 1, 3
• Posttraumatic amnesia less than 24 hours (if present) 1

Evidence-Based Diagnostic Indicators

The Brain Trauma Foundation systematic review identified four prevalent and consistent indicators that must be assessed at specific time points: 1

Immediate Assessment (Within Minutes)

• Observed and documented disorientation or confusion immediately after the event 1
• Loss of consciousness (present in less than 10% of sport-related concussions) 1
• Convulsions or tonic posturing 4
• Unusual behavior or altered mental status 1, 4

Within 24 Hours

• Impaired balance (use Balance Error Scoring System, Romberg test, or tandem gait) 1
• Ataxia 4
• Visual disturbances 4
• Neurological deficits 4

Within 48 Hours

• Slower reaction time on objective testing 1
• Impaired verbal learning and memory on cognitive assessment 1

Clinical Examination Algorithm

When evaluating suspected concussion, perform this structured assessment: 1

History:

• Mechanism of injury and events surrounding trauma 1
• Presence of loss of consciousness, amnesia, confusion 1, 4
• Number and timing of previous concussions 1
• Pre-existing conditions (mood disorders, learning disorders, ADD/ADHD, migraines) 3

Symptom Assessment: Use graded symptom checklists to document: 3, 4

• Headache (most common symptom) 5
• Dizziness 4
• Nausea 4
• Sensitivity to light/noise 4
• Feeling "in a fog" or not feeling right 4
• Difficulty concentrating 4
• Fatigue or drowsiness 4

Objective Testing:

• Cognitive function: Assess orientation, immediate/past memory, new learning, concentration using Sport Concussion Assessment Tool (SCAT) or Standardized Assessment of Concussion (SAC) 1, 3
• Balance testing: Balance Error Scoring System (BESS), Romberg test, tandem gait 1
• Neurological examination: Including gait assessment and cranial nerve testing 1

Critical Diagnostic Pitfalls

Do not rely on loss of consciousness as a required criterion—it occurs in less than 10% of sport-related concussions. 1 The absence of LOC does not exclude concussion.

Neuroimaging is typically normal in concussion by definition. 1, 2 CT or MRI should only be obtained when structural brain injury is suspected based on: 1

• Glasgow Coma Scale score less than 15 at 2 hours post-injury 1
• Suspected skull fracture 1
• Worsening headache 1
• Repeated vomiting 2
• Focal neurological deficits 2
• Altered mental status 2
• Seizures 2

Symptoms are nonspecific—you must establish temporal relationship between appropriate mechanism of injury and symptom onset. 5, 4 Symptoms not explained by another cause are required for diagnosis. 4

Concussion Subtypes

The 2020 Neurosurgery guidelines identify five predominant subtypes that guide targeted treatment (subtypes are not mutually exclusive): 1

1. Cognitive subtype: Deficits in attention, reaction time, processing speed, working memory, new learning (>1 SD below baseline or 1.5 SD below normal) 1
2. Ocular-motor subtype: Visual dysfunction and eye movement abnormalities 1
3. Headache/migraine subtype: Predominant headache symptoms 1
4. Vestibular subtype: Dizziness, balance impairment, spatial disorientation 1
5. Anxiety/mood subtype: Nervousness, emotional lability, depression, irritability 1

Associated conditions include sleep disturbance and cervical strain. 1

Distinguishing Concussion from Contusion

Concussion has normal structural neuroimaging and represents functional disturbance. 2 Contusion requires visible structural brain damage on CT or MRI. 2, 6 This distinction is critical because management differs fundamentally—contusion requires hospitalization, serial neurological exams, repeat imaging, and neurosurgical consultation. 2

Immediate Management Decision

"When in doubt, sit them out!" 2 Any athlete suspected of concussion must be immediately removed from play and not allowed same-day return. 2, 3 The athlete should be monitored for deterioration and referred to emergency department if red flag symptoms develop. 1, 2