Biomarkers of Traumatic Brain Injury and Their Relationship to Pathology

Excerpt

Traumatic brain injuries (TBIs) can occur in a number of ways and can be classified by the mechanism of injury, the clinical severity as graded by the Glasgow Coma Scale (GCS), or by the characterization of structural damage. The heterogeneity of the disease makes it difficult to accurately assess the level of trauma and predict the clinical outcome of the patient. Generally, injuries are classified as mild, moderate, or severe depending on the GCS score, which utilizes motor, eye, and verbal responses to evaluate the level of consciousness of the patient. In addition to the GCS, TBI may be classified according to a clinical injury severity score based on the level of injury incurred to various key body regions, according to the level of structural damage incurred, and according to patient prognosis based on various prognostic models. TBI injury is heterozygous in nature, and no single classification scheme is sufficient in characterizing injury for the purposes of diagnosis and prognosis. Depending on the severity of the initial insult, different imaging modalities are used to obtain the necessary information for patient care and prognosis. Whereas evidence of moderate to severe TBI is usually reliably visible as structural abnormalities using techniques such as computed tomography (CT) or conventional magnetic resonance imaging (MRI), more subtle disturbances characteristic of mild TBI are not so easily demonstrated by these imaging modalities. Mild TBI results from the main etiologies of neural contusion and axonal injury, which subsequently results in biochemical, metabolic, and cellular changes that may be responsible for some of the long-term problems seen in patients who develop postconcussion syndrome (PCS).