Acquired Brain Injury in the Elderly
THOMAS J. FARRER
JILL Z. STUART
Acquired brain injury (ABI), at any age, is a significant public health concern. It is particularly problematic in the elderly considering the increased rates of mortality and morbidity following ABI in this population. Given the expected age increase in the general population in the next several years, understanding ABI among older adults is critical in successful patient management in neurotrauma and rehabilitation settings. This is especially true given recent population-based research suggesting that as age increases, rates for hospitalization following ABI also increase (Chan, Zagorski, Parsons, & Colantonio, 2013). The following chapter will focus on the unique aspects of ABI among older adults, with a specific focus on prevention and postrehabilitation factors.
ABI consists of traumatic brain injury (TBI) and non-TBI (nTBI). Here, TBI is defined as insult to the brain after the head has been struck by or against another object. For instance, TBIs among older adults are most often caused by falls, but may also include motor vehicle accidents (MVA), assaults, or otherwise being struck by or against another object. Non-TBI is defined as an acquired injury not caused by impact or a degenerative process. This typically includes anoxic or hypoxic injury, stroke, tumor, encephalitis, meningitis, metabolic encephalopathy, and toxic effects of substances (Chan et al., 2013). Historically, ABI literature has focused on general population data and not specifically on older adults. Studies that do focus on older adults typically examine whether injury, particularly TBI, is related to or accelerates the onset of dementia. Additionally, another large portion of studies in the geriatric population is concerned with caregiver factors. Overall, considering older adults will continue to make up larger and larger portions of the population, there is a need for direct research focused in this age group.
The pathophysiology of specific types of ABIs is discussed elsewhere in this book. As such, the focus here will be on the unique aspects of pathophysiology of ABI to elderly populations. First, to understand the physiological disruption of ABI on the aging brain, it is important to understand the natural changes that occur in the brain as healthy older adults age. Research on the aging brain consistently demonstrates that there is a steady rate of volume loss as time goes by, though it is not clear whether this is due to cell death, cell morphological change, or both (Peters, 2006). There are white matter changes with age, with older adults showing signs of loss with myelin sheath deterioration beginning around age 40 (Mukherjee et al., 2002). The aging brain demonstrates changes in the synthesis of key neurotransmitter, including dopamine and serotonin (Mukherjee et al., 2002), and other chemicals important to brain health, such as brain-derived neurotrophic factors (BDNF) (Nugent et al., 2014; Peters, 2006). There is also evidence of changes in glucose metabolism, mitochondrial dysfunction, and calcium dysregulation (Melov, 2004; Peters, 2006). In addition, there are also significant microvascular changes in the aging brain that can impact physiology and cognitive functioning. These changes can lead to attenuated cerebral blood flow, reduced vascularization of brain parenchyma, and increased cerebrovascular risk. With these alterations come natural changes in cognition due to decreased ability of the brain to meet metabolic demands during cognitively demanding tasks. When taken together, natural changes in the adult aging brain—that is, changes in brain volume, white matter integrity, neurotransmitter systems, metabolic processes, and vascular changes—make the pathophysiology of ABI unique in older adults.
In the general adult population, etiology of TBI includes falls (28%), MVA (20%), struck by/against an object (19%), assault (11%), other (13%), and unknown (9%) (Langlois, Rutland-Brown, & Wald, 2006). Falls are the most common cause of TBI in the elderly, accounting for nearly 61% of TBIs among those age 65 and older. A recent, large population-based study by Chan et al. (2013) found that as age increases, the incidence of fall-related TBIs increases whereas MVA-related TBIs decreases. For nTBI, Chan and colleagues (2013) also found that from 2003 to 2009 the most common nTBI for older adults was tumors (44%), followed by anoxia (20%) and stroke (14%). Interestingly, with increased age, the percentage of nTBI due to tumor declines and the percentage of nTBI due to anoxia and stroke increases (Chan et al., 2013). In fact, advancing age is a significant risk factor for fatal stroke, with one study demonstrating that the odds of fatal stroke for adults age 86 and older was seven times that of individuals age 65 to 75 (Clarke, Blount, & Colantonio, 2011).
In the general population, the incidence of TBI in the United States is somewhere between 1.5 and 2 million cases per year, though these figures do not include individuals in the military or those treated by primary care doctors. This includes 1.4 million ER visits, of which more than 140,000 are from older adults age 65+. In fact, the highest rates of TBI-related ED visits occur among older adults who are age 75+ (Coronado, McGuire, Faul, Sugerman, & Pearson, 2013). From 2002 to 2006, the annual incidence of TBI-related hospital admissions was 275,000 with over 81,000 being older adults age 65+. Dams-O’Connor and colleagues (2013) found a 20% to 25% increase in trauma center admissions for those ≥75 years old relative to the general adult population. Although men are more likely to sustain TBIs than women in the general adult population, the study by Dams-O’Connor et al. suggests that for those age 65+, hospitalization due to TBIs was more common among White women who sustained their injury from a fall. In the general population, approximately one-third of all injury-related deaths are due to TBI (Coronado et al., 2013). The annual incidence of TBI-related deaths is approximately 51,000, with older adults accounting for more than 14,000 of these deaths (Coronado et al., 2013). Dams-O’Connor et al. (2013) demonstrated that the risk of death was greater for TBI patients with hypotension (SBP between 50 and 89 mmHg), for those with lower initial Glasgow Coma Scale (GCS) scores, and for those age 85 and older. In terms of hospitalizations, highest rates are among older adults, with 75 years old and older representing 34% of TBI-related hospitalizations. In a large population-based study in Canada, one study found that the rate of TBI-related hospitalizations increases with age (Chan et al., 2013). Specifically, this study found that for ages 65 to 74, 11% of TBI patients are hospitalized but that this number jumps to 50% for ages 75 to 84 and to 63% for those age 85+. Population data also indicated that from 1995 to 2001 and then from 2002 to 2006, incidence of TBI among older adults has increased.
In addition to age, several other factors are related to TBI risk. For instance, in the general adult population, men are twice as likely to have TBI as women (Frost, Farrer, Primosch, & Hedges, 2013), 3.4 times more likely to sustain fatal TBI, and six times more likely to die from firearm-related injuries (Corrigan, Selassie, & Orman, 2010). There is also evidence for higher rates of TBI among American Indian/Alaska Natives and African Americans relative to other ethnic groups (Corrigan et al., 2010). Alcohol use is also a well-known risk factor of TBI across all ages. Frankel et al. (2006) examined alcohol levels in older adults with TBI (age 55–89) compared with younger adults (age 16–44) and found that the presence of alcohol in the blood was more common in younger adults (44%) relative to older adults (18%), but that when present, blood alcohol levels are equivalent between groups. This study also examined day-of-injury brain CT findings in a subsample of participants and demonstrated that a midline shift of more than 5 mm was more common in older adults (31%) compared with younger adults (14%). In examining postinjury medical complications, Frankel et al. (2006) also reported that older adults had twice the incidence of seizure and urinary tract infection and three times the incidence of cardiopulmonary arrest. Such complications could certainly increase the length of stay (LOS) for older adults. Indeed, this study found that older adults had an average of 5 additional days in acute rehabilitation compared with younger adults and that this was likely responsible for significantly high inpatient rehabilitation charges for older adults. In addition, Dams-O’Connor and colleagues (2013) found that older adults with TBI were more likely to require additional in-hospital procedures such as imaging and surgery.
In terms of the impact of TBI, 43% of TBI survivors released from acute care continue to have life-long TBI-related disability (Selassie et al., 2008). Among older adults, increase in age is associated with increased chance of being released from acute care to a long-term care facility rather than home (Chan et al., 2013), which can contribute to patient and family distress, as well as financial strain. Overall, the medical–legal cost of TBI is estimated to be around US$60 billion annually, with a per-person annual cost estimated around US$45,000 (Corrigan et al., 2010). Note, however, that the cost of TBI among older adults has not been delineated in the research literature. Relatively little is known about the financial impact of nTBI in the United States. However, a large population-based study in Canada found that in the first year postinjury, the per-patient cost of nTBI is estimated to be $38,000 (CAD). The total medical cost for nTBI patients in the first year is estimated at $368 million (CAD), with a majority of the costs being accrued during acute care (Chen et al., 2012).
The incidence and prevalence of ABI among older adults is difficult to define given the variable definition of nTBI-related injuries. However, one study examined both TBI and nTBI population–based statistics from 2003 to 2009 (Chan et al., 2013). Similar to the aforementioned statistics on TBI, this study found that between 2003 and 2009, the rate of nTBI increased among older individuals and hospitalizations due to nTBI also increased with age.
As noted previously in this chapter, age is a significant risk factor for fatal stroke, with the odds of fatal stroke for individuals age 86+ being seven times higher than that of individuals age 65 to 75 (Clarke et al., 2011). The same study, which consisted of over 9,000 adults age 65+, identified education as a significant predictor of fatal stroke among older adults. Those with less than a high school education have a 95% higher odds of fatal stroke relative to older adults with a college education. Not surprisingly, older adults with comorbid diabetes and hypertension have a 50% increase in odds of incidence of stroke when followed longitudinally. In this study, lower baseline cognitive functioning was associated with a two-fold increased risk of fatal stroke, even after controlling for health-related and sociodemographic risk factors. The authors postulated that this was likely due to the fact that those with reduced cognitive functioning at baseline likely already had microvascular and white matter changes that result in reduced cognition and that this poor cerebrovascular health placed them at greater risk of future stroke.
The clinical presentation of ABI is varied, depending on the severity of the injury, etiology, and lesion location. The clinical presentation of specific types of ABIs is discoursed elsewhere in this volume. However, a few general points are discussed here. In a neurotrauma or rehabilitation setting, acute presentation of ABI would typically include injuries with acute onset such as TBI, anoxia, and stroke. In such settings, it is important to remember that level of consciousness occurs on a continuum and could include coma, vegetative state, and minimally conscious state (Kwasnica, Brown, Elovic, Kothari, & Flanagan, 2008). In addition, patients with parietal lesions may present with a lack of insight to the nature and severity of their condition. Those with left hemisphere lesions may have aphasia, with greater difficulties in comprehension occurring in posterior temporal and inferior parietal regions and more difficulty with production of speech in anterior regions, namely, the inferior frontal gyrus or Broca’s area. Given the high incidence of left middle cerebral artery involvement in stroke, it is important for neurotrauma or rehabilitation clinicians to be aware of language and communication deficits in their patients. Individuals with production aphasia (i.e., impaired expressive language and intact receptive language) tend to be more aware of their impairments and are therefore more vulnerable to depression. Regardless of the type of injury, older adults in an inpatient neurotrauma or rehabilitation setting often have compromised executive functioning (i.e., reduced decision making) and may benefit from a formal mental status or cognitive evaluation. Also, when examining patients’ mental status, it is critical to be aware of changes in vision, motor functioning, and language that would only confound test results and make the patients appear more impaired than they truly are. Individuals with TBI or stroke, depending on lesion location, may present with hemiparesis, decreased tone, and/or weakness, which would make them vulnerable to falls in an inpatient setting, especially if insight is compromised. Temporary and intermittent changes in mental status are typical for older adults in acute onset ABI. Mental status can certainly fluctuate on the basis of pain, medication changes, and time of day. Also, TBI and stroke are often associated with mood changes and agitation (Flanagan, Kwasnica, Brown, Elovic, & Kothari, 2008). Further complicating matters, individuals with a preexisting dementia may be poor narrators of their past when discussing the nature of their TBI. Additional information about such factors is discussed in the following section.
Formal diagnosis of various ABI causes may be relatively simple when given proper history and diagnostic tools (i.e., imaging and lab results). However, there are several factors that should be considered when classifying and treating certain ABIs. For example, the severity of the injury needs to be considered in all acute presentations (e.g., GCS scores, NIH Stroke Scale). This allows a treating team to better predict the patient’s course and to set realistic outcome expectations with the patient and family members. It is also important to consider the numerous confounding and comorbid factors that can influence outcomes. For example, in TBI, it would be prudent to consider the patient’s education, family history (i.e., genetic risk), premorbid functioning, comorbid medical conditions, lesion location and size, psychosocial factors, pharmacotherapy factors, and premorbid substance abuse (Moretti et al., 2012). It is common for older individuals to present in outpatient settings with concerns of memory changes and cognitive impairments, raising concerns of a mild cognitive impairment or dementia process. In this case, it is helpful to have a family member or a person close to the patient provide some history or collateral information. If a patient has a history of a brain injury or small stroke earlier in life, it may be difficult to delineate whether their current presentation is being driven by their ABI or if a new degenerative process is underway. An exacerbated cognitive decline needs to be ruled out in such cases. Here, formal neuropsychological testing and brain imaging may be helpful in determining etiology of cognitive complaints (Moretti et al., 2012).