Prior Head Injury Research Articles

Characteristics of paediatricpediatric concussion patients utilisingutilizing emergency department services prior to initial concussion clinic evaluation

ObjectiveTo evaluate characteristics of paediatric concussion patients utilising the emergency department (ED) prior to initial concussion clinic evaluation.DesignProspective cohort.SettingClinics of an American urban/suburban family practice (12/2014–04/2015).SubjectsConsented concussion patients 8–18 years presenting to clinic within 3 days of injury (n=195; age=14.3, SD=2.1 years; female=42.3%).InterventionParticipants completed a systematic evaluation at initial clinic visit and survey at 4-6 weeks (73.8% follow-up). Criterion variables included demographics, prior head injury, time of injury (TOI) factors, total symptom severity, Immediate Postconcussion Assessment and Cognitive Test (ImPACT) composites, one-month persistent symptoms, one-month Paediatric Quality of Life (PedsQL).Outcome measuresED visit before clinic evaluation (yes/no) served as the dependent variable.ResultsED visits were reported for 12.8% (n=25) of participants. Amnesia (36.0% vs. 10.1%; p<0.001), loss of consciousness (LOC) (20.8% vs. 6.7%; p=0.021), confusion (40.0% vs. 20.0%; p<0.0255), difficulty remembering (52.0% vs. 26.5%; p<0.0091), paresthesias (16.0% vs. 4.7%; p<0.0282), and CT imaging (60.0% vs. 0.6%; p<0.0001) were greater for the ED group. Initial symptom severity and ImPACT composite scores, and one-month outcomes of persistent symptoms and PedsQL, were no different for the ED group.ConclusionsPaediatric patients presenting to concussion clinic with 72 hours of injury who first visited an ED, have more dramatic symptoms at the TOI, yet do not appear to have any worse initial symptom severity, ImPACT scores, or one-month persistent symptoms or PedsQL than those who presented first to clinic. Future study should evaluate these relationships in larger samples.Competing interestsThe current study is funded in part by the National Operating Committee on Standards for Athletic Equipment.Ms. Fonseca is employed at the study setting.Ms. Phillips is employed at the study setting.Dr. Bloom is employed at the study setting.

Early traumatic brain injury screen in 6594 inpatient combat casualties

IntroductionThe purpose of this study was to review the inpatient traumatic brain injury (TBI) screening program at a Role IV regional resource trauma center. TBI has been coined the “signature wound” during current U.S. combat operations. All patients injured in Iraq or Afghanistan who transit through Landstuhl Regional Medical Center (LRMC) undergo an initial TBI screen regardless of anatomic injury. The incidence and factors associated with positive screening for concussion (physical event+alteration of consciousness (AOC)) and TBI diagnoses were examined. MethodsA retrospective review of consecutively admitted patients to LRMC who underwent a TBI screen from 5/06 to 7/11 was performed. Patient characteristics, self-reported symptoms, and TBI diagnoses were analyzed. FindingsAmong 43,852 patients screened during the 5-year period, 6594 were admitted, of whom, 6590 received a complete TBI screen. Predominantly male (97.1%), the mean age was 26.7±7.4 yrs. The average GCS and ISS at admission were 13.9±2.8 and 10.1±8.6, respectively. Positively screened patients averaged 1.8 deployments, 69.5% experienced one or more blasts, 16.1% experienced one or more vehicular crashes, with 18.0% reporting a prior head injury. Of the 2805 (42.6%) who screened positive for possible concussion, 2393 (85.3%) were diagnosed with a concussion/TBI during their inpatient stay; the remaining 412 (14.7%) were identified by screening only. Of the screened positive patients, 1953 (69.6%) reported 1 or more current concussion/TBI-related symptoms; of those with symptom(s), 532 (27.2%) reported 5 or more. ConclusionsEarly screening based on self-report identified a large number of patients admitted directly from the combat zone with possible deployment-related concussion and TBI symptoms. Such screening provides valuable information to guide decisions about early management and return to duty. Level of evidenceLevel III, Therapeutic.

Relations of blood pressure and head injury to regional cerebral blood flow

Hypertension confers increased risk for cognitive decline, dementia, and cerebrovascular disease. These associations have been attributed, in part, to cerebral hypoperfusion. Here we posit that relations of higher blood pressure to lower levels of cerebral perfusion may be potentiated by a prior head injury. Participants were 87 community-dwelling older adults — 69% men, 90% white, mean age=66.9years, 27.6% with a history of mild traumatic brain injury (mTBI) defined as a loss of consciousness ≤30min resulting from an injury to the head, and free of major medical (other than hypertension), neurological or psychiatric comorbidities. All engaged in clinical assessment of systolic and diastolic blood pressure (SBP, DBP) and single photon emission computed tomography (SPECT). Computerized coding of the SPECT images yielded relative ratios of blood flow in left and right cortical and select subcortical regions. Cerebellum served as the denominator. Sex-stratified multiple regression analyses, adjusted for age, education, race, alcohol consumption, smoking status, and depressive symptomatology, revealed significant interactions of blood pressure and head injury to cerebral blood flow in men only. Specifically, among men with a history of head injury, higher systolic blood pressure was associated with lower levels of perfusion in the left orbital (β=−3.21, p=0.024) and left dorsolateral (β=−2.61, p=0.042) prefrontal cortex, and left temporal cortex (β=−3.36, p=0.014); higher diastolic blood pressure was marginally associated with lower levels of perfusion in the left dorsolateral prefrontal cortex (β=−2.79, p=0.051). Results indicate that men with a history of head injury may be particularly vulnerable to the impact of higher blood pressure on cerebral perfusion in left anterior cortical regions, thus potentially enhancing risk for adverse brain and neurocognitive outcomes.

Suboptimal anti-epilepsy drug use is common among Indigenous patients with seizures presenting to the emergency department

We aimed to explore the causes of higher than expected rates of Indigenous emergency department (ED) seizure presentations. A questionnaire was administered to adult patients presenting with seizure to an ED in Far North Queensland. Over 15 months, among 260 presentations with seizure (22% Indigenous), 50% non-Indigenous patients, and 45% Indigenous patients completed the questionnaire. Risk factors for alcohol misuse were common in both groups (50% Indigenous, 43% non-Indigenous; p = 0.50), as were rates of reported head injury (50% Indigenous, 44% non-Indigenous; p = 0.50). However, 47% Indigenous patients, compared to 19% non-Indigenous patients ( p < 0.05) reported missing anti-epileptic tablets at least twice weekly, representing clinically relevant medication non-adherence. This was the first reported seizure presentation for 12% Indigenous patients and 26% non-Indigenous patients. We conclude that among ED seizure presentations, alcohol excess and prior head injury are commonly observed, in both Indigenous and non-Indigenous patients. However, Indigenous patients have higher rates of anti-convulsant non-adherence, likely contributing to ED presentations.

Characteristics of a Mild Head Injury Subgroup With Extreme, Persisting Distress on the Rivermead Postconcussion Symptoms Questionnaire

Kirsch NL, de Leon MB, Maio RF, Millis SR, Tan-Schriner CU, Frederiksen S. Characteristics of a mild head injury subgroup with extreme, persisting distress on the Rivermead Postconcussion Symptoms Questionnaire. Objective To examine baseline variables and identify characteristics of participants with extremely high reports of symptoms (ie, outliers) 12 months after mild head injury (MHI). Design A prospective cohort study of MHI with and without loss of consciousness (LOC) and/or posttraumatic amnesia (PTA) recruited from and interviewed at the emergency department (ED), with a follow-up telephone interview at 12 months. Setting Level II community hospital ED. Participants Participants (n=58) with MHI and LOC less than or equal to 30 minutes and/or PTA less than 24 hours and participants (n=173) with MHI but no PTA/LOC. Inclusion criteria: age greater than or equal to 18 years, less than or equal to 24 hours after injury, Glasgow Coma Scale score greater than or equal to 13, and discharge from the ED. Fourteen (6%) participants had extremely high scores on the Rivermead Postconcussion Symptoms Questionnaire (RPQ). Main Outcome Measures RPQ and questions on health services use and litigation. Results Characterizing the outlier cases are prior head injury, preinjury disability, history of substance use, unemployment, and elevated somatic symptoms at the ED. At 12 months, outliers had higher use of health services and litigation. Conclusions The existence of a subgroup with a distinctive pattern of baseline characteristics in combination with elevated somatic symptoms at the time of presentation to the ED suggests that further taxonomic distinctions may be warranted for the MHI population, each requiring appropriately targeted interventions for addressing symptomatic complaints.

Prior Head Injury and Risk for Parkinson Disease

Case-control studies have linked head injury and subsequent Parkinson disease (PD), but most have relied on self-reported head injury, which raises

Catastrophic Head Injuries in High School and College Football Players

Background Catastrophic head injuries in football are rare but tragic events. Purpose To update the profile of catastrophic head injuries in high school and college football players and to describe relevant risk factors. Study Design Case series; Level of evidence, 4. Methods We reviewed 94 incidents of severe football head injuries reported to the National Center for Catastrophic Sports Injury Research during 13 academic years (September 1989 through June 2002). Results In the study period there were an average of 7.23 (standard deviation = 2.05) direct high school and college catastrophic head injuries in scholastic football participants per year. There were 0.67 injuries per 100 000 (95% confidence interval: 0.54, 0.81 per 100 000) high school and 0.21 injuries per 100 000 (95% confidence interval: 0.0, 0.49 per 100 000) college participants for a risk ratio of 3.28 (95% confidence interval: 0.81, 13.3). The injuries resulted in subdural hematoma in 75 athletes, subdural hematoma with diffuse brain edema in 10 athletes, diffuse brain edema in 5 athletes, and arteriovenous malformation or aneurysm in 4 athletes. Fifty-nine percent of the contacts reported that the athlete had a history of a previous head injury, of which 71% occurred within the same season as the catastrophic event. Thirty-nine percent of the athletes (21 of 54) were playing with residual neurologic symptoms from the prior head injury. There were 8 (9%) deaths as a result of the injury, 46 (51%) permanent neurologic injuries, and 36 (40%) serious injuries with full recovery. Most players sustained a major impact to the head either from tackling or being tackled. Conclusion The incidence of catastrophic head injuries in football has remained low since the advent of the modern day football helmet in the early 1970s. The incidence of catastrophic head injuries in football is dramatically higher at the high school level than at the college level. Although the reason for this discrepancy is unclear, an unacceptably high percentage of high school players were playing with residual symptoms from a prior head injury. Coaches, athletes, athletic trainers, and medical personnel need to adhere to the guideline that an athlete with any neurologic symptoms from a head injury should be strongly discouraged from returning to play.

Recurrent Concussion and Risk of Depression in Retired Professional Football Players

The purpose of our study was to investigate the association between prior head injury and the likelihood of being diagnosed with clinical depression among retired professional football players with prior head injury exposure. A general health questionnaire, including information about prior injuries, the SF-36 (Short Form 36), and other markers for depression, was completed by 2552 retired professional football players with an average age of 53.8 (+/-13.4) yr and an average professional football-playing career of 6.6 (+/-3.6) yr. A second questionnaire focusing on mild cognitive impairment (MCI)-related issues was completed by a subset of 758 retired professional football players (50 yr and older). Two hundred sixty-nine (11.1%) of all respondents reported having prior or current diagnosis of clinical depression. There was an association between recurrent concussion and diagnosis of lifetime depression (chi2=71.21, df=2, P<0.005), suggesting that the prevalence increases with increasing concussion history. Compared with retired players with no history of concussion, retired players reporting three or more previous concussions (24.4%) were three times more likely to be diagnosed with depression; those with a history of one or two previous concussions (36.3%) were 1.5 times more likely to be diagnosed with depression. The analyses controlled for age, number of years since retirement, number of years played, physical component score on the SF-36, and diagnosed comorbidities such as osteoarthritis, coronary heart disease, stroke, cancer, and diabetes. Our findings suggest a possible link between recurrent sport-related concussion and increased risk of clinical depression. The findings emphasize the importance of understanding potential neurological consequences of recurrent concussion.

Neuropsychiatric Complications of Traumatic Brain Injury: A Critical Review of the Literature (A Report by the ANPA Committee on Research)

Neuropsychiatric Complications of Traumatic Brain Injury: A Critical Review of the Literature (A Report by the ANPA Committee on Research)

Head injury and Parkinson's disease risk in twins

Head injury is an inconsistently reported risk factor for Parkinson's disease (PD). Many related variables might confound this association, such as differences in childhood and adolescent lifestyles or genetically determined risk-taking behaviors. Twin studies circumvent some of these problems, because twins are genetically and environmentally much more similar than typical cases and control subjects. We conducted a case-control study in 93 twin pairs discordant for PD ascertained from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort. A prior head injury with amnesia or loss of consciousness was associated with an increased risk for PD (odds ratio, 3.8; 95% confidence interval, 1.3-11; p = 0.014). Truncating observations 10 years before PD onset enhanced the association. Though less precise, the association was somewhat stronger in monozygotic than in dizygotic pairs. Risk increased further with a subsequent head injury (p trend = 0.022) and with head injuries requiring hospitalization. Duration of unconsciousness was not associated. In a subanalysis of 18 pairs concordant for PD, the twin with younger onset PD was more likely to have sustained a head injury, although numbers were small. Our results suggest that mild-to-moderate closed head injury may increase PD risk decades later.

Head injury and brain tumours in adults: A case–control study in Rio de Janeiro, Brazil

A hospital-based case–control study exploring the association between selected risk factors and head injury in adults, brain trauma included, was carried out in Greater Metropolitan Rio de Janeiro, Brazil. Cases included adults diagnosed with primary brain tumours ( n = 231). Controls were matched for gender and age among in-patients hospitalized for various conditions unrelated to brain cancer ( n = 261) identified in the same hospitals where cases were enrolled. Risk of having experienced head injury was more frequent among cases (46%) than controls (36%) (OR adj = 1.49; 95% CI = 1.03–2.15). A dose–response effect was observed according to the number of head injuries, and a statistically borderline association was observed for meningioma (OR adj = 1.63; 95% CI = 0.96–2.75). Although recall bias cannot be ruled out, our results suggest an association between prior head injury and the development of brain tumours in adults.

The neuropsychological impact of sports-related concussion: A meta-analysis

There is increasing interest in the potential neuropsychological impact of sports-related concussion. A meta-analysis of the relevant literature was conducted to determine the impact of sports-related concussion across six cognitive domains. The analysis was based on 21 studies involving 790 cases of concussion and 2014 control cases. The overall effect of concussion (d = 0.49) was comparable to the effect found in the non-sports-related mild traumatic brain injury population (d = 0.54; Belanger et al., 2005). Using sports-concussed participants with a history of prior head injury appears to inflate the effect sizes associated with the current sports-related concussion. Acute effects (within 24 hr of injury) of concussion were greatest for delayed memory, memory acquisition, and global cognitive functioning (d = 1.00, 1.03, and 1.42, respectively). However, no residual neuropsychological impairments were found when testing was completed beyond 7 days postinjury. These findings were moderated by cognitive domain and comparison group (control group versus preconcussion self-control). Specifically, delayed memory in studies utilizing a control group remained problematic at 7 days. The implications and limitations of these findings are discussed.

A Comparison of a Preparticipation Evaluation History Form and a Symptom-Based Concussion Survey in the Identification of Previous Head Injury in Collegiate Athletes

The purpose of this study was to compare the incidence of prior head injury reported on preparticipation physical evaluation (PPE) history forms with a retrospective symptom-based survey. A comparison of 2 retrospective survey instruments. NCAA Division I varsity athletic program. A total of 93 male and 79 female athletes participating in intercollegiate contact/collision sports. Athletes were administered a concussion symptom survey (CSS) with questions about symptom incidence after head injury. These responses were compared with answers given about previous concussion/head injury on the university's PPE history form. The numbers of positive responses were analyzed using descriptive statistics, and differences between the PPE medical history form and the concussion symptom survey were assessed using chi analysis. Factor analysis was performed to assess for possible variance structure between reported symptoms. Seventy-one percent of athletes reporting symptoms consistent with concussion were not identified as having a history of head injury on the PPE medical history form. The most common symptom on the CSS was headache, which accounted for 46 (56.1%) positive responses. The CSS revealed greater numbers of athletes experiencing symptomatic head injuries than the screening questions on the PPE history form. Screening for signs and symptoms of concussion may enhance the sensitivity of the PPE in detecting a prior history of concussion.

Traumatic chiasmal syndrome: a series of 19 patients.

To present a clinical series of 19 patients with traumatic chiasmal syndrome. A retrospective study was performed. This included all patients with traumatic chiasmal syndrome seen in the neuro-ophthalmology clinic at the Royal Adelaide Hospital between January 1970 and January 2000. Of the 19 study patients, most were young males involved in motor accidents. Two-thirds had skull fractures. Three-quarters of patients had a final visual acuity of 6/12 or better in at least one eye. Ten patients had a complete optic nerve palsy. The incidence of diabetes insipidus in this study was 37%. The incidence of cranial nerve lesions, hypopituitarism, carotid cavernous fistula, and other deficits were documented. Magnetic resonance imaging and surgical findings were consistent with known mechanisms of chiasmal injury. Trauma is a rare cause of chiasmal syndrome. Patients with bitemporal field defects should be questioned about prior head injury. In the acute setting, magnetic resonance imaging is the most useful investigation. The treating practitioner should anticipate and treat associated endocrine, ocular motility, and other disorders. Mechanisms of damage to the optic chiasm after trauma include direct tearing, contusion haemorrhage and contusion necrosis. These mechanisms should not be considered mutually exclusive. Unilateral temporal hemianopia with a fellow blind eye is not necessarily the result of chiasmal disruption.

“Diagnosis Threat”: The Effect of Negative Expectations on Cognitive Performance in Head Injury

The present study examined the effect of negative expectations on neuropsychological test performance. It was hypothesized that having attention called to a history of prior head injury and the potential effects of head injury on cognition would result in diminished neuropsychological test performance relative to individuals with a similar head injury history but who did not have their attention called to their head injury history (‘diagnosis threat’). Of 36 participants with a history of mild head injury, 17 were randomly assigned to diagnosis threat and 19 to neutral test directions. The diagnosis threat group performed significantly worse on tests measuring general intellect and memory, but were not different from the neutral group in basic attention or psychomotor speed. The diagnosis threat group rated themselves as putting forth less effort on the neuropsychological battery, and self-rated effort correlated with test performance in that group. Overall, results serve as a reminder that neuropsychological tests are measures of behavior, and thus can be influenced by nonneurological factors.

Are Prior Head Injuries or Diagnostic X-Rays Associated with Glioma in Adults? The Effects of Control Selection Bias

The causes of glioma, the most common type of primary malignant brain tumors, are poorly understood. This study compares personal histories of head injury and diagnostic radiation procedures of the head and neck among 476 adults newly diagnosed with glioma in the San Francisco Bay Area between August of 1991 and April of 1994 (82% of all those diagnosed during that time period) with 462 age-, gender-, and ethnicity-frequency-matched controls (63% of those eligible from random digit dialing). In addition, limited information was obtained from 101 controls during a brief telephone interview conducted with controls who declined participation in the lengthy in-person interview. Controls who participated in the full interview were much more likely than controls who only completed the telephone interview to report head injury [odds ratios (OR) and 95% confidence intervals (CI) were 2.3 (1.0–4.9) and 3.0 (1.6–5.8) for women and men, respectively]. The OR for any head injury in cases versus controls who completed the full interview was 0.9. However, OR for any head injury in cases versus both control groups was 1.3, 95% CI (1.0–1.7), and the OR for head injury for which the subject sought medical attention was 1.1, 95% CI (0.8–1.4). Among subjects completing the full interview, cases who responded by self-report were less likely than controls to report prior non-dental head and neck X-rays (OR = 0.7; 95% CI: 0.5–1.0). However, stratification by respondents’ history of head injury indicated no difference in history of head and neck X-ray among those without prior head injury; OR 0.9; 95% CI (0.6–1.2). Cases and controls shared a very similar history of dental procedures and frequency of dental visits. These results suggest that head injury requiring medical attention, dental visits, or non-dental diagnostic X-rays to the head and neck are not important contributors to the risk of adult glioma and reveal some of the methodological obstacles encountered in forming convincing conclusions about these risk factors for brain tumors.

Neuropsychological Correlates of Domestic Violence

Neuropsychological functioning was assessed in 39 males who had committed domestic violence (batterers) and compared to 63 nonviolent (both maritally discordant and satisfied) subjects recruited by advertisement. Subjects were subsequently divided into two groups (head injured, nonhead injured) and these groups were also contrasted as a function of batterer status. Tests were administered to assess for cognitive and behavioral functions, including executive dysfunction, hypothesized to be a factor contributing to propensity for violence. Questionnaires and structured clinical interviews were used to assess marital discord, emotional distress, and violent behaviors. Batterers differed from nonbatterers across several cognitive domains: executive, learning, memory, and verbal functioning. Batterers were reliably discriminated from nonbatterers based on three neuropsychological tasks: Digit Symbol, Recognition Memory Test-Words, Wisconsin Card Sorting Test. Neuropsychological performance was the strongest correlate of domestic violence of all clinical variables measured. However, the inclusion of two other variables, severity of emotional distress and history of head injury, together with the neuropsychological indices provided the strongest correlation with batterers status. Among batterers, neuropsychological performance did not vary as a function of head injury status, indicating that while prior head injury was correlated with batterer status, it was not the sole basis for their impairments. The findings suggest that current cognitive status, prior brain injury, childhood academic problems, as well as psychosocial influences, contribute along with coexisting emotional distress to a propensity for domestic violence.

Nonepileptic seizures after head injury.

To examine the role of head injury as a risk factor in the development of nonepileptic seizures (NES). Specifically, we will determine the relative frequency of head injury among NES patients referred to our center and will describe several pertinent clinical features and personal characteristics. Retrospective record review of patients referred to our center for evaluation of seizures over a 4-year period. All patients with NES were evaluated as in a previously described protocol, which included intensive video EEG monitoring, provocation by suggestion, and psychiatric interview. All NES patients with a history of head injury were extracted for this report. Of 102 patients with NES, nearly one-third (32%) had an antecedent head injury; 52% were male, mean age was 34 years, and 12% had coexisting epilepsy. Multiple psychiatric disorders were not uncommon (79%), and a history of abuse was found in 35%. All but four patients had documented financial gain from their injury. Follow-up at 1 year found poor long-term outcome with lasting disability; despite that, the majority (91%) of head injuries were minor. Our preliminary findings suggest that prior head injury is associated with the development of NES and may contribute to the pathogenesis of NES in vulnerable patients. Head injury and sexual or physical abuse appear to occur in comparable proportions in patients with NES. This suggests that head injury and abuse may be equally important risk factors in the development of NES.

The role of head injury in cognitive functioning, emotional adjustment and criminal behaviour

In two investigations, 50 of non violent convicted felons, who avoided incarceration by participating in a day reporting programme, reported a prior history of head injury and current problems in cognitive and emotional functioning. Only 5 of a college sample in the first investigation and 15 of a community sample in the second investigation reported prior head injury. In a third investigation, 83 of felons who had reported a history of head injury also reported a date for their head injury that preceded the date of their first encounter with law enforcement. Some participants reported no trouble with the law until after experiencing a head injury that occurred in their late thirties. Considering the research reported here and elsewhere in the literature, it appears that many serious crimes follow a head injury. One implication of the findings reported here is that many crimes might not occur if people with head injury were given prompt and comprehensive treatment after the injury.

Head injury and risk of Alzheimer's disease by apolipoprotein E genotype.

Head injury and apolipoprotein E (APOE)-epsilon 4 (e4) genotype have each been associated with increased risk of Alzheimer's disease. If APOE-e4 affects neuronal viability and branching, and if response to head injury differs in e4 patients, then the association between head injury and Alzheimer's disease may vary with the presence of the e4 allele. The authors examined this association in a case-control study conducted between 1987 and 1995 among enrollees of the Group Health Cooperative of Puget Sound, a health maintenance organization in Seattle, Washington. Proxy informants reported prior head injury with loss of consciousness for 32 of 349 patients with probable Alzheimer's disease and for 16 of 342 control subjects of similar age and sex who had been randomly selected from the same population (odds ratio (OR) = 2.1, 95% confidence interval (CI) 1.1-3.8). Elevated risk was observed among men (OR = 4.2, 95% CI 1.5-11.5) but not among women (OR = 1.1, 95% CI 0.5-2.6). No significant variation in the head injury-Alzheimer's disease risk relation by APOE-e4 genotype was found among 230 cases and 309 controls (OR = 3.1 (95% CI 0.7-14.6) for persons with at least one e4 allele and OR = 2.0 (95% CI 0.8-5.2) for those without e4). Neither age, education, race, type of proxy informant, nor duration of relationship with the proxy confounded the association. Head injury with loss of consciousness, although uncommon in this sample, was associated with increased risk of Alzheimer's disease. APOE-e4 was an independent risk factor which neither modified nor confounded the association. Susceptibility to Alzheimer's disease as conferred by APOE-e4 does not appear to increase the risk associated with head injury.