TBI may result in a variety of adverse outcomes along several overlapping dimensions, including dependence, cognitive, neuropsychiatric, psychosocial, and medical comorbidity. There are several factors that affect these various outcomes after TBI, and many of these are listed in Table 69-4, including characteristics of the injury and those of the patient. These factors may interact. For example, an older patient in the prodromal phase of Alzheimer disease (AD) may exhibit progressive symptomatology of AD, which may have been instigated by the TBI but cannot readily be attributed to brain injury alone. This concept is especially relevant to age-associated brain disorders in older adults. Studies of people at risk of AD indicate that amyloid deposition and neuronal loss may occur gradually and be fairly asymptomatic until a certain threshold is reached. A brain injury, even if mild, may be sufficient to lower the threshold. Additional information on this topic is provided in the section on dementia and TBI later.
TABLE 69-4FACTORS INFLUENCING OUTCOME |Favorite Table|Download (.pdf) TABLE 69-4 FACTORS INFLUENCING OUTCOME
Severity of injury (GCS, length of coma)
Location and extent of brain tissue injury
Secondary brain injury; ICP/swelling, excitotoxicity, and hypoxia
Physics and speed of the impact
Genetic risk for neurocognitive disease
Preinjury personality and cognitive status
Access to care
Access to social and rehabilitation services
Global TBI Outcome and Age
TBI can result in long-standing cognitive, personality/emotional, and interpersonal deficits that often interfere with successful rehabilitation, resumption of employment or other responsibilities, interpersonal relations, and quality of life. A common finding is that older adults have poorer global outcome from the injury than their younger counterparts with similar injuries. The Glasgow Outcome Scale (GOS), a simple five-point scale ranging from death to good recovery (Table 69-5), is the predominant outcome instrument for global outcome. However, this measure is quite coarse. Despite its limitations, this scale has been used in the largest number of patients and trials. In a recent pooled analysis of the International Mission for Prognosis and Clinical Trial (IMPACT) data involving more than 8700 patients with GOS outcome scores, results indicated that age is one of the most powerful prognostic indictors of GOS outcome, as is acute GCS motor score, pupil response, and computed tomography findings. In the case of severe injury, the chance of a GOS good recovery is unlikely in the geriatric patient. Three studies have found that among patients older than 65 years who sustained severe injury (GCS ≤ 8), none exhibited a good recovery on the GOS. Another study found that only 6% of patients older than 65 years exhibit good recovery after severe TBI. A fifth study suggested that good recovery was possible after severe injury if the patient regained consciousness within 72 hours. Even when the injury is mild or moderate, older adults have poorer GOS outcome.
With regard to rehabilitation outcomes, an important study of TBI model systems data found that patients older than 55 years experienced a doubling in the length of rehabilitation stay and associated costs, while only attaining half the rate of functional recovery of their younger counterparts. These patients also had greater cognitive impairments at discharge and higher rates of nursing home placement.
Less research has been done with fine-tuned neuropsychological assessment of outcome, and studies tend to be much smaller. A review of major cognitive domains that are affected in TBI follows.
TABLE 69-5GLASGOW OUTCOME SCALE |Favorite Table|Download (.pdf) TABLE 69-5 GLASGOW OUTCOME SCALE
|OUTCOME ||SCALE ||DESCRIPTOR |
|Death ||1 || |
|Vegetative state ||2 ||Unable to interact with environment; unresponsive. |
|Severe disability ||3 ||Conscious, but dependent—in need of supervision/assistance every day as a result of physical and cognitive impairments. Ranges from total dependency to assistance with one or more ADLs. |
|Moderate disability ||4 ||Independent but with a disability. Basic ADLs are intact, but the patient is impaired in occupational and/or social functioning. Able to work in a supported environment. |
|Good recovery ||5 ||The patient has mild to no residual deficits and has the capacity to resume independent occupational and social activity. |
Cognitive Outcomes: Executive Dysfunction
The selective vulnerability of the frontal and temporal lobes to injury gives rise to a preponderance of neuropsychological deficits involving frontal systems, including executive functions, working memory, speed of processing, episodic memory, and aspects of personality. All have been shown to be related to severity of injury. The precise definition of executive function is itself a matter of debate and some confusion. The executive functions are those that promote self-directed action. Self-monitoring, self-regulation, inhibition, introspective reflection, decision making, and planned and goal-directed activity are executive functions. Working memory and attentional capacity such as imperviousness to distraction and sustained attention are necessary components, but not sufficient by themselves for executive function. However, these capacities are conveniently operationalized into a quantifiable psychometric instrument (such as digit span, n-back, or serial 7s), and there is a great deal of research on these components of executive function. Executive functions and components are best assessed with a comprehensive neuropsychological evaluation, although some bedside tests such as clock draw, verbal fluency, digit span, and go-no-go tests may be useful to get a feel for the extent of the problem.
Speed of information processing is one of the most frequently observed deficits after TBI. For example, one study found patient’s reaction time in a simple motor choice paradigm to be significantly slower than that of matched young adults. Another study assessed speed of information processing and attention in a group of 60 patients with severe TBI and controls. When speed of processing was statistically controlled, differences between patients and controls in focused and divided attention became nonsignificant, suggesting that slowed information processing was accounting for most of the difference. A similar finding was observed for planning and flexible problem solving in patients with severe TBI in the chronic stage of recovery. When speed was controlled, performance was equivalent between patients and controls. A factor analysis of a battery of neuropsychological test scores in survivors of TBI indicated that the most prominent factor was decreased perceptual and motor speed. Speed of processing also declines with age, and thus the older patient with TBI may have unusually slow cognitive processing speeds, greatly limiting their range of activities and quality of social interactions.
The ability to allocate attention between multiple tasks, and working memory is affected in TBI. For example, Baddeley’s original model of working memory, which has been frequently proposed to help explain executive difficulties, states that a central executive process or supervisory attentional system within the prefrontal heteromodal cortex regulates the allocation of limited attentional resources. This system appears to be facilitated by D2 dopamine networks within the dorsolateral frontal lobe and is particularly vulnerable to trauma through either direct contact (contusion to the lateral frontal lobe) or disconnection via acceleration/deceleration injuries.
Memory complaints from patients are extremely common following TBI, and measured impairment seen on neuropsychological tests is frequently observed, including difficulty at the encoding or acquisition stage, as well as difficulty in retrieval of information. Whether these complaints and deficits are secondary to the more salient attentional, processing speed and executive deficits or whether these are a primary result of hypoxic and excitotoxic injury to the hippocampus is still somewhat unresolved and may vary depending on the nature and severity of the injury.
The personality changes accompanying TBI vary depending on the injury location, severity, and preinjury personality factors. Prigatano has summarized the literature in detail on this point. Common overlapping descriptors of personality in patients with TBI include irritability/anger, impatience, impulsivity, poor social judgment, inappropriate social behavior, rapid mood swings, loss of drive, fatigability, and/or depression. Major ways of relating to the world following TBI have been described as “childishness” (self-centered behavior, insensitivity to others, or immature behaviors), “helplessness and dependence” (requiring supervision and inability to make important decisions or set goals), and “lack of insight/awareness” of any of the above difficulties. These patterns frequently overlap and have been collectively labeled “frontal lobe personality.”
TBI results in very abrupt changes that may not be easily (and often only gradually) accommodated into one’s stable sense of self. Characteristics of impaired self-awareness can be varied depending on injury location and severity. Acutely, patients with TBI may be unaware that they have deficits from the injury. Later, the patient may admit to some deficits but fail to appreciate the impact of these deficits on daily functioning. Prigatano et al. found that patients with TBI frequently underestimated their behavioral limitations, abnormalities in social interaction, and emotional dyscontrol when compared to a family member’s rating of the patient’s abilities, while more objective criterion-based competencies, such as instrumental activities of daily living (IADLs), may be areas where the patient’s insight is more accurate. Critically, a syndrome of impaired self-awareness will significantly complicate or impede the rehabilitation process or treatment adherence, since patients may not perceive the need for such treatments. Damage to the anterior medial prefrontal regions (behind the forehead) has been associated with impaired self-awareness for social interaction, judgment, and planning. These are common sites of injury with TBI as described above.