The cognitive presentation is variable. Difficulties in the domains of complex attention, executive ability, learning, and memory are common as well as slowing in speed of infor- mation processing and disturbances in social cognition. In more severe TBI in which there is brain contusion, intracranial hemorrhage, or penetrating injury, there may be additional neurocognitive deficits, such as aphasia, neglect, and constructional dyspraxia.
Major or mild NCD due to TBI may be accompanied by disturbances in emotional function (e.g., irritability, easy frustration, tension and anxiety, affective lability); personality changes (e.g., disinhibition, apathy, suspiciousness, aggression); physical disturbances (e.g., headache, fatigue, sleep disorders, vertigo or dizziness, tinnitus or hyperacusis, pho- tosensitivity, anosmia, reduced tolerance to psychotropic medications); and, particularly in more severe TBI, neurological symptoms and signs (e.g., seizures, hemiparesis, visual disturbances, cranial nerve deficits) and evidence of orthopedic injuries.
In the United States, 1.7 million TBIs occur annually, resulting in 1.4 million emergency de- partment visits, 275,000 hospitalizations, and 52,000 deaths. About 2% of the population lives with TBI-associated disability. Males account for 59% of TBIs in the United States.
The most common etiologies of TBI in the United States are falls, vehicular accidents, and being struck on the head. Collisions and blows to the head that occur in the course of con- tact sports are increasingly recognized as sources of mild TBI, with a concern that repeated mild TBI may have cumulatively persisting sequelae.
The severity of a TBI is rated at the time of injury/initial assessment as mild, moderate, or severe according to the thresholds in Table 2.
The severity rating of the TBI itself does not necessarily correspond to the severity of the resulting NCD. The course of recovery from TBI is variable, depending not only on the specifics of the injury but also on cofactors, such as age, prior history of brain damage, or substance abuse, that may favor or impede recovery.
Loss of consciousness <30 min 30 minutes—24 hours >24 hours
Neurobehavioral symptoms tend to be most severe in the immediate aftermath of the
TBI. Except in the case of severe TBI, the typical course is that of complete or substantial improvement in associated neurocognitive, neurological, and psychiatric symptoms and signs. Neurocognitive symptoms associated with mild TBI tend to resolve within days to weeks after the injury with complete resolution typical by 3 months. Other symptoms that may potentially co-occur with the neurological symptoms (e.g., depression, irritability, fatigue, headache, photosensitivity, sleep disturbance) also tend to resolve in the weeks following mild TBI. Substantial subsequent deterioration in these areas should trigger con- sideration of additional diagnoses. However, repeated mild TBI may be associated with persisting neurocognitive disturbance.
With moderate and severe TBI, in addition to persistence of neurocognitive deficits, there may be associated neurophysiological, emotional, and behavioral complications.
These include seizures (particularly in the first year), photosensitivity, hyperacusis, irritabil- ity, aggression, depression, sleep disturbance, fatigue, apathy, inability to resume occu- pational and social functioning at pre-injury level, and deterioration in interpersonal relationships. Moderate and severe TBI have been associated with increased risk of depres- sion, aggression, and possibly neurodegenerative diseases such as Alzheimer’s disease.