j_neurotrauma_submission_16-apr-2014

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nly/Not for Distribution

Journal of Neurotrauma: http://mc.manuscriptcentral.com/neurotrauma

Prospective Examination of the Effects of Combat-related

Mild Traumatic Brain Injury: Does Blast mTBI History Matter?

Journal: Journal of Neurotrauma

Manuscript ID: Draft

Manuscript Type: Regular Manuscript

Date Submitted by the Author: n/a

Complete List of Authors: Kontos, Anthony; University of Pittsburgh, Orthopaedic Surgery ELbin, RJ; University of Arkansas, Office for Sport Concussion Research Kotwal, Russ; Joint Trauma System, US Army Institute of Surgical Research Lutz, Robert; U.S. Army Special Operations Command, Kane, Shawn; U.S. Army Special Operations Command, Forsten, Robert; 121st Combat Support Hospital, US Army Medical Activity, Collins, Michael; University of Pittsburgh, Orthopaedic Surgery

Keywords: ADULT BRAIN INJURY, HEAD TRAUMA , MILITARY INJURY, TRAUMATIC BRAIN INJURY, PROSPECTIVE STUDY

Mary Ann Liebert, Inc, 140 Huguenot Street, New Rochelle, NY 10801

Journal of Neurotrauma

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nly/Not for Distribution mTBI and Blast History

1

Prospective Examination of the Effects of Combat-related Mild Traumatic Brain

Injury: Does Blast mTBI History Matter?

Anthony P. Kontos, Ph.D.,1 R.J. Elbin Ph.D.,

2 Russ S. Kotwal, M.D., M.P.H.,

3 Robert H.

Lutz, M.D.,4 Shawn Kane, M.D.,

4 Peter J. Benson, M.D.

4, Robert D. Forsten, D.O.,

5

Michael W. Collins, Ph.D.1

1 – The University of Pittsburgh Medical College Sports Medicine Concussion Program,

Pittsburgh, PA

2 – University of Arkansas, Office for Sport Concussion Research, Fayetteville, AR

3 - Joint Trauma System, US Army Institute of Surgical Research, San Antonio, TX

4 – U.S. Army Special Operations Command, Fort Bragg, NC

5 – 121st Combat Support Hospital, US Army Medical Activity- Korea, Seoul, South

Korea

Corresponding Author: Anthony P. Kontos, Ph.D., Assistant Research Director,

UPMC Sports Medicine Concussion Program, Associate Professor Department of

Orthopaedic Surgery, University of Pittsburgh School of Medicine, 3200 South Water

Street, Pittsburgh, PA 15203, (412) 432-3725, [email protected].

Total Word Count: 3,836

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Abstract

The effects of mild traumatic brain injury (mTBI) have received significant attention

since the beginning of the conflicts in Afghanistan and Iraq. Surprisingly, little is known

about the temporal nature of neurocognitive impairment, mTBI and post-traumatic stress

(PTS) symptoms following combat-related mTBI. It is also unclear as to the role that

blast exposure history has on mTBI and PTS impairments and symptoms. The purpose of

this study was to examine prospectively the effects of mTBI on neurocognitive

performance, and mTBI and PTS symptoms among US Army Special Operations

Command (USASOC) personnel; and to study the influence of previous history of blast

mTBI on these effects. Eighty USASOC personnel with (n=19) and without (n=61) a

history of blast-related mTBI completed the military version of the Immediate Post-

Concussion Assessment Cognitive Test (ImPACT), Post Concussion Symptom Scale

(PCSS), and the PTSD Checklist (PCL) at baseline, as well as 1-7 days and 8-20 days

following a combat-related mTBI. Results indicated that verbal memory (p=.002) and

processing speed (p=.003) scores were significantly lower and mTBI symptoms (p=.001)

were significantly higher at 1-7 days post-injury compared to both baseline and 8-20 days

post-injury. Post-traumatic stress remained stable across the three time periods.

Participants with a history of blast mTBI demonstrated lower verbal memory at 1-7 days

post mTBI compared to participants without a history of blast mTBI (p=.02). Decreases

in neurocognitive performance and increased mTBI symptoms are evident 1-7 days

following combat-related mTBI, and a history of blast-related mTBI may influence these

effects.

Key Words: mTBI, blast, PTSD, neurocognitive, military

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Introduction

Mild traumatic brain injury (mTBI) is a signature injury sustained by military

personnel during the conflicts in Afghanistan and Iraq1 and accounts for 76% of all brain

injuries reported from 2001 – 2011 in US military personnel (http://www.dvbic.org/TBI-

Numbers.aspx). The estimated lifetime prevalence rate of mTBI among military

personnel is 19.5%.2 However, in spite of these data and due in part to logistic challenges

in combat environments, few studies have assessed the immediate effects of combat-

related mTBI in military personnel. Moreover, Kontos et al.3 reported that combat-related

mTBI exposure was associated with residual neurocognitive impairment and increases in

post-traumatic stress (PTS) symptoms and clinical levels of post-traumatic stress disorder

(PTSD). In addition, the decreases in neurocognitive function and increased PTS

symptoms reported in Kontos et al.3 were further exacerbated by the number of previous

exposures to combat-related mTBI (i.e., dose response). Further investigation of these

relationships is warranted as there is a need to develop a better understanding of the

mTBI and PTS symptoms and cognitive impairments immediately following combat-

related mTBI, and factors that may influence these outcomes in military personnel.

The primary mechanisms of mTBI in military personnel involve blast, blunt, and

blast-blunt combination injuries resulting from exposure to improvised explosive devices

(IEDs), falls, and motor vehicle collisions.4 Blast-related injuries are classified into

primary, secondary, tertiary, and quaternary blast injury types and are more prevalent as

an mTBI mechanism.5,6 Primary blast injuries involve exposure to high-force blast waves

that produce mechanical projectiles (i.e., missile fragments) and secondary blast injury

results in military personnel being forcefully thrown following exposure. Tertiary blast

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injuries involve collapsing debris, and exposure to fires and noxious fumes are examples

of quaternary blast injury types.6,7 Blunt mTBI results from falls and motor vehicle

collisions that produce acceleration-deceleration forces to the head. Blast-blunt

combination injuries involve both blast and blunt mechanisms.

The signs and symptoms of mTBI include headache, dizziness, fatigue,

inattention, depression, imbalance, memory dysfunction, and slowed reaction time.1,8,9

Within one week of injury the majority of mTBI symptoms cluster into a primary

cognitive-migraine-fatigue symptom factor with additional and less pronounced somatic,

affective, and sleep factors.10 The mTBI symptoms that persist beyond one week post-

injury cluster into more distinct emotional, migraine/somatic, cognitive, and sleep

factors.11 The symptom presentations observed in military personnel with mTBI are

similar to the sequelae documented in athletes with sport-related mTBI.12 If mismanaged,

these impairments may lead to prolonged impairment, with recent reports showing that

the prevalence of chronic mTBI symptoms ranges from 15 to 30%.13 Moreover, PTS

symptoms that commonly overlap with mTBI symptoms occur in up to 40% of U.S.

military personnel who have had mTBI.14 Baseline levels of PTS symptoms are higher

for military personnel with previous exposure to blast-related mTBI.3 These findings

stress the importance of proper assessment and management of mTBI in military

personnel, and continued investigation of the effects of exposure to mTBI.

Despite the potential deleterious effects of the aforementioned impairments and

symptoms on combat performance and quality of life, the majority of military personnel

with mTBI underestimate the seriousness of this injury and do not seek medical

attention.15 Similar to military personnel, many athletes also minimize and avoid

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reporting mTBI symptoms to medical professionals.16 Due to potential self-report

limitations and shortcomings of relying on subjective reports (e.g., inaccurate symptom

reporting) more objective assessments for mTBI are often employed. Computerized

neurocognitive testing (e.g., Automated Neuropsychological Assessment Metrics

[ANAM]; military version of the Immediate Post-concussion Assessment and Cognitive

Test [ImPACT]) is one tool that provides more objective data on the effects of mTBI in

military personnel.

Although computerized neurocognitive testing has been used in the military for

over a decade, little is known about the acute (i.e., 24-72 hours) and sub-acute (i.e., 3-21

days) cognitive effects of mTBI when assessed in the combat environment. Kelly and

colleagues17 compared the cognitive performance of soldiers with mTBI to healthy and

injured controls within 72 hours post-injury using the ANAM battery. They reported that

soldiers with mTBI demonstrated significant decreases in performance on simple reaction

time, procedural reaction time, and code substitution, compared to both control groups.

Although this was the first study to document the acute (i.e., within 72 hours of injury)

cognitive effects of combat-related mTBI among military personnel, these data were

limited to a small sample of cases (N= 34) that included only post-injury assessments.17

Moreover, the researchers did not assess the effects of mTBI beyond the 72 hour time

period. These researchers also did not examine potential differences in post-mTBI

neurocognitive performance between blast and blunt mechanisms of injury or the

influence of mTBI history on subsequent post-mTBI cognitive performance. Previous

research3 has documented that a history of blast-related mTBI is associated with worse

baseline performance on visual memory and reaction time than a history of blunt mTBI

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or no history of mTBI. In addition, these researchers reported that individuals with prior

exposure to blast-related mTBI demonstrated increased PTS symptoms. However, little is

known about the interaction between mTBI history and current mTBI on cognitive

impairments, symptoms and PTS following subsequent mTBI in military personnel.

The primary purpose of the current study was to examine prospectively the effects

of mTBI on neurocognitive performance, and mTBI and PTS symptoms among US Army

Special Operations Command (USASOC) personnel. A secondary purpose of the study

was to examine the role of history of blast mTBI on the above outcomes. We

hypothesized that cognitive impairments and symptoms would be evident following

mTBI and that a history of blast mTBI would worsen these outcomes.

Materials and Methods

Participants and Design

A prospective, repeated measures design involving assessments of neurocognitive

performance, mTBI and PTS symptoms was conducted between December 2009 and

March 2012. A total of 276 USASOC personnel (Age, M = 28.68 years, SD = 6.40) with

a diagnosed mTBI were included in the initial sample for this study. The majority of the

sample was currently deployed (80%, n= 220) and male (99%, n= 273). Individuals were

excluded from the study if they had a history of diagnosed moderate to severe TBI, brain

surgery, major psychiatric disorder, or neurological disorder. In addition, participants

were included only if reliable data were available for mechanism of injury and previously

diagnosed mTBI history. Finally, participants were included if they completed the

measures described below at baseline (pre-injury), and 1-7 and 8-20 days post-injury

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intervals. The resulting sample of 80 all male participants represented a total response

rate of 28% of the original sample of 276 USASOC personnel.

Definition of mTBI

For the current study, a diagnosed mTBI involved presentation with signs (e.g.,

loss of consciousness, disorientation/confusion, amnesia) and symptoms (e.g., dizziness,

headache) of an mTBI with confirmatory diagnoses through follow-up clinical

assessments by USASOC medical personnel. All injuries in the current study were

characterized by Glasgow Coma Scale (GCS) scores of 15 with no abnormal findings on

structural imaging (i.e. CT Scan, MRI).

Instrumentation

Neurocognitive Performance, mTBI Symptoms, and PTS Symptoms

A military version of the Immediate Post-Concussion Assessment Cognitive Test

(ImPACT) was used to assess neurocognitive performance. The military version of this

test also comprises the following sections: 1) demographics, 2) the Post-concussion

Symptom Scale (PCSS), and 3) post-traumatic stress disorder (PTSD Checklist: PCL).

The neurocognitive assessment is comprised of six subtests: 1) verbal memory, 2) design

memory, 3) X’s and O’s, 4) symbol matching, 5) color matching, and 6) three letter

memory. The six neurocognitive subtests are collapsed into four composite scores

including verbal memory, visual memory, visual motor processing speed, and reaction

time (RT). Demographic data include age, sex, migraine history, deployment status,

testing location, military rank, and military occupational specialty. The PCSS contains 22

self-report symptoms rated on a 0 (none) to 6 (severe) point Likert scale. The PCL

encompasses 17 items and requires individuals to indicate on a scale of 1 (not at all) to 5

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(extremely) how much each item bothered them during the past month. The PCL yields a

PTSD symptom score that ranges from 17-85. Clinical PTSD cut-offs for the PCL were

set at 28 or higher, per current guidelines for recent veterans of combat in Afghanistan

and Iraq.18-20

Procedures

This study was approved by both the University of Pittsburgh and Womack Army

Medical Center institutional review boards for human subject research. Each participant

individually completed the web-based military version of the PCSS, PCL, and military

ImPACT tests at baseline and approximately 1-7 and 8-21 days post injury.

Data Analysis

Descriptive analyses were conducted to describe the sample and mechanism of

mTBI (e.g., blunt or blast/combination) for participants. The sample was divided into two

mutually exclusive groups based on history of medically diagnosed mTBI since joining

USASOC: 1) history of blast mTBI, or 2) no blast mTBI history. It is important to note

that some participants in the no blast mTBI history group may have had previous

exposure to blunt mTBI. A series of 2 (blast mTBI history) x 3 (time) repeated measures

ANOVAs with Bonferroni correction for multiple comparisons were used to compare

changes in neurocognitive performance, mTBI symptoms and PTS symptoms from

baseline to 1-7 and 8-20 days post-injury. The independent variables were history of

diagnosed blast mTBI and time (baseline, 1-7 days, and 8-21 days post injury).

Dependent variables were scores on the ImPACT composites (verbal and visual memory,

processing speed, and reaction time), total PCSS, and total PCL symptom scores. Data

were analyzed using SPSS Version 20 (IBM).

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Results

Descriptive Data and mTBI Mechanisms and Previous mTBI Exposure among USASOC

Personnel

A summary of descriptive demographic data for the blast mTBI history and no

history groups as well as the total sample is provided in Table 1. The results of a series of

independent samples t-tests and chi-square analyses (mTBI mechanism, history of

medical diagnosed blunt mTBI) supported significant differences between the blast mTBI

history groups on age (t= -2.25, p=.03) and height (t= -2.28, p=.03). The blast mTBI

history group was slightly older (31.05 +/- 7.07 yrs) and taller (180.61 +/- 5.86cm) than

the no history group (27.54 +/- 5.57 yrs; 176.59 +/- 6.95 cm). The breakdown of mTBI

mechanisms was as follows: 29% (23/80)- blunt mTBI, 21% (17/80)- blast/combination

mTBI. The mTBI mechanisms for 50% (40/80) of the injuries in this sample were

unknown/undocumented. One-third (26/80) of the sample reported a history of at least

one medically diagnosed blunt mTBI and 24% (19/80) reported a history of at least one

medically diagnosed blast/combination mTBI.

Changes in Neurocognitive Performance, Symptoms, and Post-Traumatic Stress

Symptoms Across Time

The results from a series of 2 diagnosed history of blast mTBI group (none, blast

mTBI history) x 3 time periods (baseline, 1-7 and 8-20 days) repeated measures

ANOVAs revealed significance within subjects main effect for time on verbal memory (F

[2, 77]= 6.71, p= .002), processing speed (F [2, 77]= 6.19, p= .003) and mTBI symptoms

(F [2, 77]= 14.28, p= .001). A summary of the main effect for time on neurocognitive

performance, mTBI symptoms and PTS symptoms is presented in Table 1. Specifically,

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the results indicated that verbal memory and processing speed scores were significantly

lower and mTBI symptoms were significantly higher at 1-7 days post-injury compared to

both baseline and 8-20 days post-injury. Although visual memory and reaction time were

not statistically lower at 1-7 days post-injury compared to baseline and 8-20 days post-

injury, the results did support a clinically meaningful trend across these time periods.

Post-traumatic stress symptoms remained constant across the three time periods.

Interaction between Diagnosed Blast mTBI History and Time on Neurocognitive

Performance, mTBI Symptoms, and PTS Symptoms

The results from a series of 2 diagnosed history of blast mTBI group (none, blast

mTBI history) x 3 time periods (baseline, 1-7 and 8-20 days) repeated measures

ANOVAs supported one interaction between a history of diagnosed blast mTBI and time

on verbal memory (F [2, 77]= 4.08, p=.02). A summary of the results for these analyses

is presented in Table 3. Specifically, verbal memory scores were lower at 1-7 days and 8-

20 days post injury than baseline for the diagnosed history of blast mTBI group but not

for the no history of blast mTBI group (see Figure 1). There were non-significant, but

clinically relevant trends for lower performance on visual memory, processing speed, and

reaction time and higher mTBI symptoms at 1-7 days post-injury compared to baseline

for the diagnosed history of blast mTBI group compared to the no blast mTBI history

group. However, there were no such trends for PTS symptoms, which remained

essentially stable across each of the three time points (see Table 3).

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Discussion

Overview of Key Findings

In the current study we prospectively examined changes in neurocognitive

performance, mTBI and PTS symptoms from baseline to 1-7 and 8-20 days post-injury

among USASOC personnel who sustained a mTBI. We also investigated the role that

previous history of blast mTBI had on subsequent neurocognitive outcomes and mTBI

and PTS symptom reports. There were several key findings in this study: 1) decreases in

neurocognitive performance (i.e., verbal memory, processing speed) and increases in

mTBI symptoms were detected during the first 7 days following mTBI in USASOC

personnel; 2) PTS symptoms remained stable from baseline to 20 days post-injury; and 3)

USASOC personnel with a prior history of blast mTBI demonstrated worse

neurocognitive performance during the first week following mTBI on verbal memory

compared to those without history of blast mTBI. These findings provide partial support

for our hypotheses and demonstrate the effects of mTBI on neurocognitive performance

and symptom reports in USASOC personnel. These findings also underscore the

importance of the role of previous exposure to blast mTBI on subsequent mTBI outcomes.

General Discussion

The current findings support and extend previous research that has examined the

adverse effects of mTBI on cognitive performance and symptom reports in military

populations. In a small sample of military personnel (n = 34) assessed within 72 hours of

mTBI, Kelly et al.17 documented significant changes in simple and procedural reaction

time, code substitution, and matching compared to non-injured, matched controls.

However, Kelly and colleagues17 did not measure these outcomes beyond the initial 72

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hour acute period following mTBI. The current study extended the previous study and

demonstrated decreased neurocognitive performance up to 7 days post injury, with a

return to pre-injury neurocognitive performance and mTBI symptoms within 8 - 20 days.

This return to pre-injury levels at 8-20 days provides some evidence that the current

clinical practice guidelines implemented by USASOC medical personnel for assessing

and managing mTBI are effective in reducing the long term effects of this injury.

Statistical decreases in neurocognitive performance within the first week

following mTBI were supported for verbal memory and processing speed, but not for

visual memory and reaction time. Although not statistically significant, performance on

visual memory and reaction time was lower at 1-7 days post-injury compared to baseline

levels. It is important to note that these statistically non-significant trends may still be

clinically relevant, as they support a general decline in neurocognitive performance in the

first week following injury.

In addition to the neurocognitive findings, as expected, total mTBI symptoms

were significantly higher compared to baseline at 1-7 days post-injury, but were not

significantly elevated at 8-20 days post injury. In contrast to this increase in mTBI

symptoms, PTS symptom scores remained stable from baseline to both post-injury time

intervals. This finding suggests that some of the initial effects of mTBI previously

attributed to PTS among military personnel, may in fact, be a direct result of the mTBI

instead. Given the purposeful selection for resiliency among USASOC personnel, the

changes associated with PTS may not manifest at all, may manifest later in the process or

only after multiple exposures to potential PTS-inducing stimuli, such as mTBI in this

sample. Resiliency has been reported to be a moderator of stress associated with military

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deployment,21 and “highly cohesive” military units with strong social support are

reported to be more resilient to high combat exposure as well as depression and PTS.22

Given the short period of time after mTBI exposure (no more than 20 days) in the current

study, PTS symptoms in this population may not manifest for months to years following

blast exposure as documented in previous research.15 Extricating PTS from mTBI-

particularly in the early phases of the injury- is further complicated by the number of

overlapping symptoms of both PTS and mTBI.23 Given this potential overlap between

symptoms of PTS and mTBI and previous findings, the lack of increased PTS symptom

reports following mTBI requires additional study and should be interpreted cautiously

secondary to the chronic course of both PTS and mTBI.

Previous research has supported the relationship between mTBI symptoms and

PTSD symptoms,24 but many of these studies focus on chronic mTBI and PTSD

symptom reporting.25-27

Little is known regarding the acute PTS symptom presentation

and its relationship to acute mTBI symptoms, as measured in the current study. There

may be a bias among USASOC personnel to minimize PTS symptoms in the days and/or

weeks following mTBI due to the fear of the consequences of a behavioral health referral

(e.g., being withheld from active duty/combat), stigma associated with reporting PTS

symptoms, and the potential for receiving a PTSD diagnosis.28 The time course of PTS

and mTBI symptom reporting warrants additional study in order to better understand the

temporal nature of how these symptoms emerge and develop following mTBI and if a

history of blast mTBI influences the development of PTSD.

In the current study, USASOC personnel with a history of blast mTBI performed

worse on verbal memory one week following mTBI compared to those without a history

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of blast mTBI. This finding is consistent with previous research by Kontos et al.,3 which

reported that a history of blast mTBI was associated with lower baseline neurocognitive

performance. However, there were no differences on verbal memory in the current

sample at baseline; only at 1-7 days post-injury. Therefore, a history of previous blast

mTBI may amplify the initial effects of subsequent mTBIs. It is noteworthy that the

verbal memory scores of individuals with a history of previous exposure to blast mTBI

returned to pre-injury levels by 8-20 days. This finding indicates that although personnel

with a history of blast mTBI may experience more significant initial impairment

following a subsequent mTBI, with proper clinical management their impairments are

short-lived. However, if these potentially at-risk personnel are returned to active duty too

early when they are still suffering from the effects of this injury, these initial effects may

be prolonged or worsened.

There were no differences between history of previous exposure to blast mTBI

groups on current mTBI and PTS symptoms. This finding is in contrast to the residual

effects on mTBI and PTS symptoms reported by Kontos and colleagues.3 One reason for

this finding is that USASOC personnel may deny or minimize their PTS symptoms in

order to remain active with their units and avoid potential stigma associated with PTSD

in the military. Alternately, USASOC personnel may lack insight into their PTS

symptoms in the period immediately following exposure to mTBI. In the current study,

we did not differentiate among levels of exposure to previous blast mTBIs. Moving

forward, researchers should examine the potential interaction between history of previous

exposure to blast mTBI and current mTBI mechanism on outcomes. In so doing,

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researchers may be able to determine if these previous exposures to blast mTBI

compound the effects of subsequent blast/combo and blunt mTBIs, equally.

Limitations

As with any research, there were some limitations to the current study. Due to the

inherent challenges in obtaining complete and accurate medical records during active

combat environments there was a low overall response rate (29%, 80/276) from among

all USASOC personnel who met initial inclusion criteria. We were able to obtain reliable

information for only 50% of the current mTBI mechanisms (e.g., blast/combo, blunt).

Blast sensor data were unavailable in this study. Therefore, the amount of force at impact

whether previous or current, blunt or blast, could not be measured and incorporated into

our analyses. Consequently, we were unable to examine potential differences in

outcomes based on current mTBI mechanism or the interaction between current

mechanism and a history of previous exposure to blast mTBI. The use of self-reported

PTS and mTBI symptom data are limited in that they rely on subjective reporting. Also,

we assumed that respondents were honest and accurate in their responses. The entire

sample was comprised of males, which limits the generalizability of the current findings

to male military personnel only. As such, the sex differences in recovery outcomes

following mTBI in civilian sport populations reported by researchers29,30

could not be

examined in the current study sample. Finally, the study sample was delimited to

USASOC personnel, who represent a selective sub-sample that may not be generalizable

to the overall US Army and US Military populations.

Implications

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Neurocognitive impairment and symptoms were detected on average up to one-

week in USASOC personnel following mTBI. We believe that computerized

neurocognitive testing can be a useful tool for medical providers use as part of a

comprehensive mTBI post-injury assessment to guide return to full duty and participation

in follow on combat operations. Neurocognitive data, in combination with information

about balance, vestibular, oculomotor and other assessments, can help inform better

clinical decision-making and identify personnel who are potentially at-risk, but do not

report symptoms. Additionally, these data can be used to better inform military leaders

regarding the impact of such events on personnel, and to promote conservative

management strategies and adherence to clinical practice guidelines as warranted.

Based on the current findings, military medical professionals should consider the

history of previous exposure to blast mTBI when evaluating patients who have incurred a

subsequent mTBI. For sustained combat operations- as evidenced by nearly 13 years of

conflict- a risk benefit analysis may be warranted as military leaders consider the

repetitive use of the same personnel from a relatively small all-volunteer force to conduct

frequent missions involving likely exposure to mTBI mechanisms. Potential multiple

exposures to blast forces and other mTBI mechanisms may result in adverse, residual

long-term health implications for these at-risk military personnel.

Conclusion

In conclusion, the present study demonstrated that neurocognitive deficits in

verbal memory and processing speed and an increase in reported mTBI symptoms

following mTBI in USASOC personnel are evident in the first week, but resolve within 8

– 20 days following injury. However, these increases were not observed for PTS

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symptoms, which remained stable and low from baseline through 8-20 days post-injury.

Importantly, a history of exposure to previous blast mTBI appears to exacerbate initial

impairment and symptoms following a subsequent mTBI exposure. As such, clinicians

should identify these at-risk personnel for more conservative and targeted clinical

management to mitigate the effects of previous history of exposure to blast mTBI on

subsequent mTBIs. However, the current findings suggest that personnel with a previous

history of exposure to blast mTBI recovered to pre-injury neurocognitive and symptom

levels by 8-20 days, similar to personnel with no history of blast mTBI. Therefore,

current clinical practice guidelines for managing this injury implemented by USASOC

medical personnel may be helping to improve outcomes even in these at-risk personnel.

Author Disclosure Statement

Dr. Collins owns a 10% share in ImPACT Applications, Inc. With regard to the study

data, Dr. Collins was not involved in data collection, entry or analysis; he was only

involved in data interpretation.

Disclaimer

This research was funded by the U.S. Special Operations Command Biomedical

Initiatives Steering Committee. The views expressed herein are those of the author(s) and

do not reflect the official policy of the Department of the Army, Department of Defense,

or the U.S. Government. Citations of commercial products or organizations do not

constitute an official DoD endorsement or approval of the products or services of these

organizations. This report was approved for public release by the U.S. Army Special

Operations Command Operational Security Office and Public Affairs Office on April,15,

2014, and the U.S. Army Medical Department Public Affairs Office on April 15, 2014.

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29. Covassin, T., Schatz, P., Swanik, C.B. (2007). Sex differences in

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nly/Not for DistributionTable 1. Summary of Demographic Data, mTBI Mechanism, and History of Medically

Diagnosed Blast mTBI.

Measures

History of Medically

Diagnosed Blast

mTBI (n= 19)

M (SD)

No History

(n= 61)

M (SD)

Total Sample

(N= 80)

M (SD)

Age* 31.05 (7.07) 27.54 (5.57)

Height (cm)* 180.61 (5.86) 176.59 (6.95)

Weight (kg) 86.56 (10.68) 82.11 (9.79)

# (%) # (%) # (%)

mTBI Mechanism

Blunt

Blast/Combination

Undocumented

4 (21%)

6 (32%)

9 (49%)

19 (31%)

11 (18%)

31 (51%)

23 (29%)

17 (21%)

40 (50%)

History of Blunt

mTBI

4 (21%) 22 (36%) 26 (33%)

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nly/Not for DistributionTable 2. Summary of the Neurocognitive Performance and mTBI and PTS Symptom

Scores at Baseline, 1-7, and 8-20 Days Post-injury (N= 80).

*p<.01, **p<.001; a - lower than baseline and 8-20 days;

b - higher than baseline and 8-20

days.

Measures

Baseline

M (SD)

1-7 days

M (SD)

8-20 days

M (SD)

Verbal Memory-%* 77.55 (11.74) 74.39 (12.47)a 77.93 (11.51)

Visual Memory- % 69.93 (14.45) 67.10 (15.79) 68.30 (17.10)

Processing Speed* 26.27 (4.11) 25.21 (5.36)a 27.29 (5.47)

Reaction Time- sec 0.596 (0.097) 0.612 (0.109) 0.593 (0.108)

mTBI Symptoms** 6.45 (11.50) 18.68 (21.55)b 10.56 (14.43)

PTS Symptoms 19.18 (6.19) 20.55 (7.45) 20.55 (8.02)

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nly/Not for DistributionTable 3. Summary of the Interaction between Diagnosed History of Blast mTBI and Time

on Neurocognitive Performance, mTBI and PTS Symptoms (N= 80).

*p<.05

Measures/Groups

Baseline

M (SD)

1-7 days

M (SD)

8-20 days

M (SD)

Verbal Memory-%*

History of Blast mTBI

No History

80.92 (7.05)

77.55 (11.74)

70.25 (16.27)

75.67 (10.87)

76.70 (13.22)

78.31 (11.01)

Visual Memory- %


No History

69.96 (14.09)

69.93 (14.68)

66.36 (13.32)

67.33 (16.58)

64.93 (16.93)

69.35 (17.16)

Processing Speed


No History

26.12 (4.09)

26.32 (4.15)

23.02 (4.89)

25.90 (5.35)

26.35 (4.36)

27.58 (5.72)

Reaction Time- sec


No History

0.577 (0.068)

0.602 (0.104)

0.635 (0.069)

0.604 (0.118)

0.605 (0.093)

0.589 (0.113)

mTBI Symptoms


No History

6.53 (9.78)

6.43 (12.03)

24.11 (22.66)

16.98 (21.09)

9.11 (10.23)

11.02 (15.56)

PTS Symptoms


No History

18.21 (3.18)

19.48 (6.86)

20.84 (6.34)

20.46 (7.81)

20.36 (8.26)

20.61 (8.01)

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nly/Not for Distribution

254x190mm (72 x 72 DPI)

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j_neurotrauma_submission_16-apr-2014

Documents

effects of mtbi

combatrelated mtbi

mtbi history matter

blast history

effects of combat

adult brain injury

military injury

exposure history