MILD TRAUMATIC BRAIN INJURY AND THE POSTCONCUSSIVE SYNDROME

Abstract

There are more than 6 million cases of traumatic brain injury (TBI) in the United States per year, most of which are categorized as mild. Surprisingly, there is no one set of universally accepted criteria for the classification of TBI. 5 , 8 The following * * From Mild Traumatic Brain Injury Committee of the Head Injury Interdisciplinary Special Interest Group of the American Congress of Rehabilitation Medicine: Definition of mild traumatic brain injury. J Head Trauma Rehab 8:86–87, 1993; with permission. presents those criteria used by the American Congress of Rehabilitation Medicine. 30 Any period of loss of consciousness of <30 min and Glasgow Coma Scale score of 13–15 after this period of loss of consciousness Any loss of memory for events immediately before or after the accident, with post-traumatic amnesia of <24 hours Any alteration in mental state at the time of the accident (e.g., feeling dazed, disoriented, or confused) Focal neurologic deficit(s) that may or may not be transient Severity of TBI frequently is graded according to the Glasgow Coma Scale score (GCS) into mild (score of 13–15), moderate (score of 9–12), and severe (score of 3–8). The GCS score is not predictive of the presence of an intracranial lesion, however. Ten percent to 20% of patients with a GCS score above 12 have positive findings on head CT. 16 , 38 Consequently, some investigators have recommended that positive CT findings be used to distinguish complicated mild TBI from uncomplicated cases, that is, cases with normal CTs. 45 Mild TBI characteristically is associated with some degree of altered level of consciousness or amnesia. The presence and duration of these findings have been used to divide mild TBI into subsets. 27 No study has demonstrated definitively that post-traumatic amnesia or the length of time of unconsciousness predicts symptoms after mild TBI. 4 , 21 , 17 Despite the fact that most classification schemes group patients with a GCS score of 13 to 15 into a “mild” category, in actuality, patients with a GCS less than 15 most likely have a greater degree of neuronal damage and are at a higher risk of sequelae . Although the GCS score is frequently used to grade TBI, the timing of when the score is determined varies considerably in the literature. One GCS score determination is not sufficient for assessing the severity of a head injury. Conversely, the initial GCS score is a critical reference point when comparing patient groups and making a prognostic judgment. 41 The postconcussive syndrome (PCS) refers to a symptom complex experienced by many patients after TBI. 10 , 29 , 36 In general, PCS comprises of somatic, cognitive, and affective symptoms: Somatic Headache Sleep disturbance Dizziness/vertigo Nausea Fatigue Oversensitivity to noise/light Cognitive Attention/concentration problems Memory problems Affective Irritability Anxiety Depression Emotional lability Thirty percent to 80% of patients with mild TBI report symptoms at 3 months postinjury, 7 , 35 whereas up to 15% continue to be symptomatic at 1 year postinjury. 3 The percentage of symptomatic patients is higher for patients with moderate and severe TBI. Severe TBI has received the most attention in recent years, whereas diagnostic and management strategies for mild TBI remain poorly defined. The lack of uniformity in the definition of mild TBI and failure of studies to use comparative assessments in categorizing patients makes interpretation of much of the mild TBI literature difficult at best. Studies not only vary in their entry criteria but also often are flawed owing to failure to obtain adequate follow-up information, absence of control groups, and lack of standardization in neuroimaging and neuropsychologic testing. This article attempts to present the current understanding of the pathophysiology of mild TBI and the subsequent natural history of the PCS. Physicians providing acute care must be aware of the PCS so that patients can be properly counseled and appropriate follow-up care can be arranged.