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 3, 2
- Glasgow Coma Scale score of 13-15 2, 4
- Loss of consciousness less than 30 minutes (if present) 3, 4
- Posttraumatic amnesia less than 24 hours (if present) 3
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) 5
- Convulsions or tonic posturing 6
- Unusual behavior or altered mental status 3, 6
Within 24 Hours
- Impaired balance (use Balance Error Scoring System, Romberg test, or tandem gait) 1
- Ataxia 6
- Visual disturbances 6
- Neurological deficits 6
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: 5
History:
- Mechanism of injury and events surrounding trauma 7
- Presence of loss of consciousness, amnesia, confusion 3, 6
- Number and timing of previous concussions 7
- Pre-existing conditions (mood disorders, learning disorders, ADD/ADHD, migraines) 4
Symptom Assessment: Use graded symptom checklists to document: 4, 6
- Headache (most common symptom) 8
- Dizziness 6
- Nausea 6
- Sensitivity to light/noise 6
- Feeling "in a fog" or not feeling right 6
- Difficulty concentrating 6
- Fatigue or drowsiness 6
Objective Testing:
- Cognitive function: Assess orientation, immediate/past memory, new learning, concentration using Sport Concussion Assessment Tool (SCAT) or Standardized Assessment of Concussion (SAC) 5, 4
- Balance testing: Balance Error Scoring System (BESS), Romberg test, tandem gait 5
- Neurological examination: Including gait assessment and cranial nerve testing 5
Critical Diagnostic Pitfalls
Do not rely on loss of consciousness as a required criterion—it occurs in less than 10% of sport-related concussions. 5 The absence of LOC does not exclude concussion.
Neuroimaging is typically normal in concussion by definition. 5, 2 CT or MRI should only be obtained when structural brain injury is suspected based on: 5
- Glasgow Coma Scale score less than 15 at 2 hours post-injury 5
- Suspected skull fracture 5
- Worsening headache 5
- 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. 8, 6 Symptoms not explained by another cause are required for diagnosis. 6
Concussion Subtypes
The 2020 Neurosurgery guidelines identify five predominant subtypes that guide targeted treatment (subtypes are not mutually exclusive): 7
- Cognitive subtype: Deficits in attention, reaction time, processing speed, working memory, new learning (>1 SD below baseline or 1.5 SD below normal) 7
- Ocular-motor subtype: Visual dysfunction and eye movement abnormalities 7
- Headache/migraine subtype: Predominant headache symptoms 7
- Vestibular subtype: Dizziness, balance impairment, spatial disorientation 7
- Anxiety/mood subtype: Nervousness, emotional lability, depression, irritability 7
Associated conditions include sleep disturbance and cervical strain. 7
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, 9 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, 4 The athlete should be monitored for deterioration and referred to emergency department if red flag symptoms develop. 5, 2