What is Mild Traumatic Brain Injury (MTBI)?

Mild Traumatic Brain Injury (MTBI): Definition and Characteristics

Mild traumatic brain injury (MTBI) is defined as an acute brain injury resulting from mechanical energy to the head characterized by a Glasgow Coma Scale (GCS) score of 14-15, with one or more of the following: confusion/disorientation, loss of consciousness for 30 minutes or less, post-traumatic amnesia for less than 24 hours, or transient neurological abnormalities. 1

Key Diagnostic Criteria

MTBI is distinguished from other forms of traumatic brain injury by specific criteria:

• GCS Score: 14-15 (patients with GCS 13 are often excluded from the "mild" category due to higher risk of requiring neurosurgical intervention) 2
• Loss of Consciousness: Brief, less than 30 minutes 2
• Post-traumatic Amnesia: Less than 24 hours 2
• Mental State Alteration: Feeling dazed, disoriented, or confused at the time of injury 2
• Imaging: Normal structural imaging (if obtained) 2

Terminology Clarification

• The terms "MTBI" and "concussion" are often used interchangeably in clinical practice 2, 3
• "Mild" refers to the severity of the initial physical trauma that caused the injury, not the severity of consequences or symptoms 2
• "Head injury" and "brain injury" are distinct entities - head injury refers to clinically evident physical trauma (lacerations, ecchymoses), while traumatic brain injury refers specifically to injury to the brain itself 2

Clinical Significance and Outcomes

Despite being classified as "mild," MTBI can have significant consequences:

• 3-13% of patients with GCS 15 will have an acute lesion on head CT 2
• Less than 1% require neurosurgical intervention 2
• Up to 15% of MTBI patients may have compromised function one year after injury 2, 1
• Approximately half of individuals with a single MTBI may demonstrate long-term cognitive impairment 4

Post-Concussive Sequelae

MTBI can result in two distinct phases of symptoms:

1. Early Phase Post-Traumatic Disorder:

   • Acute symptoms including headache, dizziness, imbalance, fatigue, sleep disruption, impaired cognition
   • Typically resolves in days to weeks
   • Related primarily to brain trauma and concomitant injuries 5

2. Late Phase Post-Traumatic Disorder:

   • Evolves from early phase in a minority of patients
   • More prolonged symptoms (months to years)
   • Influenced by psychosocial factors
   • History of multiple concussions increases risk of more severe and longer duration symptoms 5

Limitations of Current Definitions

• No universal definition for MTBI exists 2
• The Glasgow Coma Scale was not originally designed to diagnose mild or moderate TBI 2
• A single GCS score has limited prognostic value for MTBI and is insufficient to determine the degree of parenchymal injury 2
• The CDC acknowledges that GCS alone can lead to misclassification of TBI 2

Clinical Pitfalls and Caveats

• The term "mild" can be misleading, as many patients experience significant disability from MTBI
• Diagnosis is particularly challenging at the least severe end of the MTBI spectrum, especially when relying on subjective, retrospective accounts 5
• Postconcussive syndrome is a controversial concept due to varying criteria and symptom overlap with other disorders 5
• The VA/DoD's updated definition of TBI no longer recommends using GCS to diagnose TBI 2

MTBI represents a significant clinical challenge requiring careful assessment and management to prevent long-term consequences and improve patient outcomes.