Handbook of Clinical Neurology, Vol. 127 (3rd series) Traumatic Brain Injury, Part I J. Grafman and A.M. Salazar, Editors © 2015 Elsevier B.V. All rights reserved
Chapter 9
Mild traumatic brain injury DOUGLAS I. KATZ1,2*, SARA I. COHEN2,3, AND MICHAEL P. ALEXANDER4,5,6 1 Department of Neurology, Boston University School of Medicine, Boston, MA, USA 2
Acquired Brain Injury Program, Braintree Rehabilitation Hospital, Braintree, MA, USA
3
Department of Physical Medicine and Rehabilitation, Tufts Medical School, Boston, MA, USA 4
Concussion/TBI Program, Beth Israel Deaconess Medical Center, Boston, MA, USA 5
Spaulding Hospital Cambridge, Cambridge, MA, USA
6
Department of Neurology, Harvard Medical School, Boston, MA, USA
DEFINITIONS AND DIAGNOSTIC CRITERIA Mild traumatic brain injury Mild traumatic brain injury is among the most common neurologic conditions but precise definition and accurate diagnosis remain problematic. Traumatic brain injury (TBI) is typically classified along a continuum of severity, conventionally divided into mild, moderate, and severe categories. Traditional definitions rely on early clinical features to define the least severe end of the continuum, mild TBI. The term also implies the least severe end of the pathophysiologic continuum but clinical pathophysiologic diagnosis of mild TBI remains elusive due to the usual absence of objective findings on standard clinical imaging or any other measures. To date, biomarkers of the pathophysiologic effects of mild TBI are not established for clinical use to confirm diagnosis or injury severity, though there is promise in neuroimaging technologies such as diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS), and protein biomarkers such as S100b and neuron-specific enolase (Muller et al., 2007; Topolovec-Vranic et al., 2011). Clinical criteria regarding the depth and duration of impaired consciousness and anterograde amnesia define the inclusive range for mild TBI. Mild TBI is defined as acute neurophysiologic brain dysfunction resulting from impact contact forces or sudden acceleration/deceleration causing a transient
alteration of consciousness and/or a period of anterograde (and possibly retrograde) amnesia. The diagnostic criteria defining alteration of consciousness at the least severe end are the most problematic, usually described as the subjective experience of feeling dazed or disoriented and/or being unable to account for seconds or minutes of events after the injury. The accuracy and specificity of such criteria for confirming a mild TBI are lacking. Other factors and experiences such as the physiologic effects of an adrenaline rush or effects of intoxication might cause similar transient experiences of altered awareness. The subjectivity of this criteria, often based on remote, retrospective recall, adds to the imprecision and unreliability of this diagnosis. At the higher level of the range of severity, the criteria for distinguishing mild TBI from moderate TBI are somewhat arbitrary, for instance, setting limits at particular durations of unconsciousness or amnesia. Although the criteria delimit the lowest end of the entire TBI severity continuum, the conventional definitions of mild TBI include a notably broad range of severity, from momentary disorientation to hours of post-traumatic amnesia. Adding to the complexity is the possibility of focal brain lesions or other bodily injuries that contribute to the mix determining symptom profiles and outcomes. There are three widely used definitions of mild TBI and one recently established for military screening. The first of these, established in 1993 by the American Congress of Rehabilitation Medicine (ACRM, 1993), defines
*Correspondence to: Douglas I. Katz, MD, Acquired Brain Injury Program, Braintree Rehabilitation Hospital, 250 Pond Street, Braintree, MA 02184, USA. Tel: +1-781-348-2265, Fax: +1-781-380-4809, E-mail: [email protected]
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mild TBI as an alteration of brain function caused by external forces with one or more of the following: ● ● ● ●
loss of consciousness (LOC) lasting 0–30 minutes post-traumatic amnesia (PTA) lasting less than 24 hours focal neurologic deficits that may or may not be transient an alteration of mental state at the time of the accident, which includes any sort of confusion, disorientation, or slowed thinking.
If LOC exceeds 30 minutes, PTA lasts greater than 24 hours, or the Glasgow Coma Scale score (GCS) is less than 13 after 30 minutes, the patient is diagnosed as having a more severe traumatic brain injury. The ACRM criteria were the first not to require a LOC in the definition, and a general consensus has been reached that documentation of PTA is sufficient for a diagnosis of mild TBI (Ruff, 2005). The US Centers for Disease Control and Prevention (CDC) definition of mild TBI is even less specific than that of ACRM in that it includes any period of observed or self-reported transient confusion, disorientation, or impaired consciousness, dysfunction of memory around the time of the incident, and loss of consciousness lasting less than 30 minutes. According to this definition, there may or may not be signs of neurologic or neuropsychological dysfunction, such as headache, dizziness, or fatigue (National Center for Injury Prevention and Control, 2003) (see also Ch. 1). In 2004, the World Health Organization (WHO) Collaborating Centre for Neurotrauma Task Force on Mild Traumatic Brain Injury proposed a definition of mild TBI based on review of the literature. Their criteria are similar to the ones proposed by ACRM, but specify use of the GCS score of 13–15 at time of presentation to a healthcare professional instead of restricting it to a score
within 30 minutes, since it is a practical concern that the patient may not be assessed within 30 minutes (Carroll et al., 2004a). More recently, in 2009, the Department of Veterans Affairs in the US issued a Clinical Practice Guideline for the management of concussion and mild TBI. This guideline established similar criteria to that of ACRM for diagnosis of brain injury in combat soldiers, with the additional requirement that the alteration of consciousness lasts less than 24 hours and that structural imaging is normal (Department of Veterans Affairs, 2009). Due to the high incidence of reported mild TBI in military personnel returning from combat (Hill et al., 2009), it is important to have strict guidelines to differentiate mild TBI from non-TBI pathology, especially when there is a large overlap in the symptoms of mild TBI and post-traumatic stress syndrome (PTSD) (Menon et al., 2010). Using the established guidelines (summarized in Table 9.1), accurate diagnosis of mild TBI is still a challenge because of the frequent presence of confounding factors (Menon et al., 2010). In many cases, clinicians rely on LOC or PTA that is self-reported and unreliable or from fragmented information from witnesses. Psychogenic amnesia due to acute stress from the injury may further conceal the actual symptoms at the time of the event. Alcohol, recreational drugs, or centrally acting medications used near the time of injury may also result in memory gaps or alteration of consciousness that can confound the clinical diagnosis of a brain injury.
“Complicated” mild TBI Some patients meet clinical criteria for mild TBI but have positive findings on neuroimaging such as subarachnoid hemorrhage or small contusions. This presentation has
Table 9.1 Definitions of mild TBI
Organization American College of Rehabilitation Medicine Centers for Disease Control World Health Organization Department of Veterans Affairs
Loss of consciousness
Posttraumatic amnesia
, lasting 0–30 min
Chapter 9
Mild traumatic brain injury DOUGLAS I. KATZ1,2*, SARA I. COHEN2,3, AND MICHAEL P. ALEXANDER4,5,6 1 Department of Neurology, Boston University School of Medicine, Boston, MA, USA 2
Acquired Brain Injury Program, Braintree Rehabilitation Hospital, Braintree, MA, USA
3
Department of Physical Medicine and Rehabilitation, Tufts Medical School, Boston, MA, USA 4
Concussion/TBI Program, Beth Israel Deaconess Medical Center, Boston, MA, USA 5
Spaulding Hospital Cambridge, Cambridge, MA, USA
6
Department of Neurology, Harvard Medical School, Boston, MA, USA
DEFINITIONS AND DIAGNOSTIC CRITERIA Mild traumatic brain injury Mild traumatic brain injury is among the most common neurologic conditions but precise definition and accurate diagnosis remain problematic. Traumatic brain injury (TBI) is typically classified along a continuum of severity, conventionally divided into mild, moderate, and severe categories. Traditional definitions rely on early clinical features to define the least severe end of the continuum, mild TBI. The term also implies the least severe end of the pathophysiologic continuum but clinical pathophysiologic diagnosis of mild TBI remains elusive due to the usual absence of objective findings on standard clinical imaging or any other measures. To date, biomarkers of the pathophysiologic effects of mild TBI are not established for clinical use to confirm diagnosis or injury severity, though there is promise in neuroimaging technologies such as diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS), and protein biomarkers such as S100b and neuron-specific enolase (Muller et al., 2007; Topolovec-Vranic et al., 2011). Clinical criteria regarding the depth and duration of impaired consciousness and anterograde amnesia define the inclusive range for mild TBI. Mild TBI is defined as acute neurophysiologic brain dysfunction resulting from impact contact forces or sudden acceleration/deceleration causing a transient
alteration of consciousness and/or a period of anterograde (and possibly retrograde) amnesia. The diagnostic criteria defining alteration of consciousness at the least severe end are the most problematic, usually described as the subjective experience of feeling dazed or disoriented and/or being unable to account for seconds or minutes of events after the injury. The accuracy and specificity of such criteria for confirming a mild TBI are lacking. Other factors and experiences such as the physiologic effects of an adrenaline rush or effects of intoxication might cause similar transient experiences of altered awareness. The subjectivity of this criteria, often based on remote, retrospective recall, adds to the imprecision and unreliability of this diagnosis. At the higher level of the range of severity, the criteria for distinguishing mild TBI from moderate TBI are somewhat arbitrary, for instance, setting limits at particular durations of unconsciousness or amnesia. Although the criteria delimit the lowest end of the entire TBI severity continuum, the conventional definitions of mild TBI include a notably broad range of severity, from momentary disorientation to hours of post-traumatic amnesia. Adding to the complexity is the possibility of focal brain lesions or other bodily injuries that contribute to the mix determining symptom profiles and outcomes. There are three widely used definitions of mild TBI and one recently established for military screening. The first of these, established in 1993 by the American Congress of Rehabilitation Medicine (ACRM, 1993), defines
*Correspondence to: Douglas I. Katz, MD, Acquired Brain Injury Program, Braintree Rehabilitation Hospital, 250 Pond Street, Braintree, MA 02184, USA. Tel: +1-781-348-2265, Fax: +1-781-380-4809, E-mail: [email protected]
132
D.I. KATZ ET AL.
mild TBI as an alteration of brain function caused by external forces with one or more of the following: ● ● ● ●
loss of consciousness (LOC) lasting 0–30 minutes post-traumatic amnesia (PTA) lasting less than 24 hours focal neurologic deficits that may or may not be transient an alteration of mental state at the time of the accident, which includes any sort of confusion, disorientation, or slowed thinking.
If LOC exceeds 30 minutes, PTA lasts greater than 24 hours, or the Glasgow Coma Scale score (GCS) is less than 13 after 30 minutes, the patient is diagnosed as having a more severe traumatic brain injury. The ACRM criteria were the first not to require a LOC in the definition, and a general consensus has been reached that documentation of PTA is sufficient for a diagnosis of mild TBI (Ruff, 2005). The US Centers for Disease Control and Prevention (CDC) definition of mild TBI is even less specific than that of ACRM in that it includes any period of observed or self-reported transient confusion, disorientation, or impaired consciousness, dysfunction of memory around the time of the incident, and loss of consciousness lasting less than 30 minutes. According to this definition, there may or may not be signs of neurologic or neuropsychological dysfunction, such as headache, dizziness, or fatigue (National Center for Injury Prevention and Control, 2003) (see also Ch. 1). In 2004, the World Health Organization (WHO) Collaborating Centre for Neurotrauma Task Force on Mild Traumatic Brain Injury proposed a definition of mild TBI based on review of the literature. Their criteria are similar to the ones proposed by ACRM, but specify use of the GCS score of 13–15 at time of presentation to a healthcare professional instead of restricting it to a score
within 30 minutes, since it is a practical concern that the patient may not be assessed within 30 minutes (Carroll et al., 2004a). More recently, in 2009, the Department of Veterans Affairs in the US issued a Clinical Practice Guideline for the management of concussion and mild TBI. This guideline established similar criteria to that of ACRM for diagnosis of brain injury in combat soldiers, with the additional requirement that the alteration of consciousness lasts less than 24 hours and that structural imaging is normal (Department of Veterans Affairs, 2009). Due to the high incidence of reported mild TBI in military personnel returning from combat (Hill et al., 2009), it is important to have strict guidelines to differentiate mild TBI from non-TBI pathology, especially when there is a large overlap in the symptoms of mild TBI and post-traumatic stress syndrome (PTSD) (Menon et al., 2010). Using the established guidelines (summarized in Table 9.1), accurate diagnosis of mild TBI is still a challenge because of the frequent presence of confounding factors (Menon et al., 2010). In many cases, clinicians rely on LOC or PTA that is self-reported and unreliable or from fragmented information from witnesses. Psychogenic amnesia due to acute stress from the injury may further conceal the actual symptoms at the time of the event. Alcohol, recreational drugs, or centrally acting medications used near the time of injury may also result in memory gaps or alteration of consciousness that can confound the clinical diagnosis of a brain injury.
“Complicated” mild TBI Some patients meet clinical criteria for mild TBI but have positive findings on neuroimaging such as subarachnoid hemorrhage or small contusions. This presentation has
Table 9.1 Definitions of mild TBI
Organization American College of Rehabilitation Medicine Centers for Disease Control World Health Organization Department of Veterans Affairs
Loss of consciousness
Posttraumatic amnesia
, lasting 0–30 min
