Neuropsychiatric Outcomes in UK Military Veterans With Mild Traumatic Brain Injury and Vestibular Dysfunction
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J Head Trauma Rehabil
Copyright
c 2018 Wolters Kluwer Health, Inc. All rights reserved.
Neuropsychiatric Outcomes in UK
Military Veterans With Mild Traumatic
Brain Injury and Vestibular
Dysfunction
Emma Denby, BSc; Dominic Murphy, PhD; Walter Busuttil, MBBS; Mohamed Sakel, MBBS;
David Wilkinson, PhD
Objective: To estimate the frequency of vestibular dysfunction following blunt, blast, and combined blunt and
blast mild traumatic brain injury (mTBI) and thereon assess the long-term impact of vestibular dysfunction on
neurobehavioral function and disability independently of comorbid psychiatric symptoms. Setting: Combat Stress
residential and Veterans’ Outreach drop-in centers for psychological support. Participants: One hundred sixty-
two help-seeking UK military veterans. Main Measures: Self-reported frequency and severity of mTBI (using the
Ohio State TBI Identification Method), Vertigo Symptom Scale, PTSD Checklist for DSM-5, Kessler Psychological
Distress Scale (K10), Neurobehavioral Symptom Inventory, Headache Impact Test (HIT6), Memory Complaints
Inventory, World Health Organization Disability Assessment Schedule II short version (WHODAS 2.0). Results:
Seventy-two percent of the sample reported 1 or more mTBIs over their lifetime. Chi-square analyses indicated
that vestibular disturbance, which affected 69% of participants, was equally prevalent following blunt (59%) or
blast (47%) injury and most prevalent following blunt and blast combined (83%). Mediation analysis indicated
that when posttraumatic stress disorder, depression, and anxiety were taken into account, vestibular dysfunction
in participants with mTBI was directly and independently associated with increased postconcussive symptoms and
functional disability. Conclusion: Vestibular dysfunction is common after combined blunt and blast mTBI and
singularly predictive of poor long-term mental health. From a treatment perspective, vestibular rehabilitation may
provide relief from postconcussive symptoms other than dizziness and imbalance. Key words: balance, blast, blunt,
mTBI, veterans
B
Author Affiliations: School of Psychology, University of Kent,
Canterbury, United Kingdom (Ms Denby and Dr Wilkinson); Combat
ETWEEN THE PERIODS OF 2003-2011, there
Stress, Tyrwhitt House, Leatherhead, United Kingdom (Dr Murphy and were 2440 UK casualties in Operations Herrick
Mr Busuttil); King’s Centre for Military Health Research, King’s College, (Afghanistan) and TELIC (Iraq).1 Approximately 19%
London, United Kingdom (Dr Murphy); and East Kent Neuro-
Rehabilitation Service, East Kent Hospitals University, NHS Foundation
of casualties sustained a traumatic brain injury (TBI)
Trust Canterbury, United Kingdom (Mr Sakel). and although 87% were graded as moderate-to-severe,
E.D. was supported by an internal PhD studentship from KentHealth, Uni-
estimates derived from US personnel give reason to be-
versity of Kent. lieve that the incidence of mild TBI (mTBI) was likely
The authors thank all study participants for their patient cooperation. They
underreported.2 mTBI acquired during combat is signif-
are also grateful to Professors William Milberg and Gina McGlinchey at icantly associated with long-term neurobehavioral and
the Translational Research Center for TBI and Stress Disorders, Boston VA psychiatric (most notably posttraumatic stress disorder
Medical Center (USA), for their conceptual and methodological help with
the study design and selection of outcome measures. They also thank Dr Paul
[PTSD]) disturbance and is a risk factor for alcohol abuse
Green for his invaluable advice on the use and interpretation of the Memory and general disability. Elevated exposure to munitions
Complaints Inventory. explosions leave military personnel uniquely suscepti-
Supplemental digital content is available for this article. Direct URL citations ble to blast-induced mTBI, which, perhaps unsurpris-
appear in the printed text and are provided in the HTML and PDF versions ingly, is associated with damage to the vestibular or-
of this article on the journal’s Web site (www.headtraumarehab.com).
gans of the inner ear. Vestibular injury can also be sus-
The authors declare no conflicts of interest. tained through blunt injury to the back of the head via
Corresponding Author: David Wilkinson, PhD, School of Psychol-
ogy, University of Kent, Canterbury, Kent CT2 7NP, United Kingdom
(dtw@kent.ac.uk). DOI: 10.1097/HTR.0000000000000468
1
Copyright © 2018 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.2 JOURNAL OF HEAD TRAUMA REHABILITATION
projectile or fall. Of particular interest here, studies in ized as audiological impairment, vestibular impairment
civilians show overlap in the neurobehavioral and psy- can be induced by the blast wave from a nearby mu-
chiatric symptoms that accompany vestibular dysfunc- nitions explosion that induces an overpressurization,
tion and mTBI. Coupled with the fact that vestibular followed by an underpressurization, in the air and fluid-
assessment is not routinely performed on military per- filled chambers of the inner ear.10 The mechanical dam-
sonnel, this raises the possibility that some symptoms age caused by such a blast wave can be compounded
that are vestibular in origin have been misattributed by noise-induced damage (typically >140 dB), toxin
to mTBI. In the present study, we compared the rel- exposure, and, if the individual falls over and bangs
ative prevalence of vestibular symptoms in blast and the back of the head or is hit by a projectile, blunt
blunt mTBI in help-seeking UK veterans to determine injury.11 Aside from causing middle and inner ear dam-
the group most at risk of vestibular-related impairment. age, white matter abnormalities and diffuse axonal in-
We then determined the contribution of vestibular dys- jury have been observed in cerebellum, thalamus, and
function to neuropsychiatric function and more general ventral posterior cerebral cortex in mTBI patients pre-
disability. senting with vestibulopathy.12 The presence of these
The estimated incidence of mTBI ranges between abnormalities has been shown to correlate with time
15%3 and 23%4 in US personnel to between 3.2%5 and to recovery and neurocognitive test performance. Un-
13.5% in UK personnel.1,6 Several factors may help ex- fortunately, vestibular symptoms are among the most
plain this discrepancy including the greater reliance on common after mTBI. In the large-scale study (n = 907)
self-report rather than medical records in the United conducted by Terrio et al,4 dizziness and balance prob-
States and the shorter deployment periods of UK sol- lems were the second most commonly reported symp-
diers (6 months compared with 12-18 months for US tom reported by individuals immediately after sustain-
personnel). There is, however, an emerging consensus ing mTBI, with 11.5% reporting persistent problems
that the effects of mTBI sustained during deployment postdeployment. In a case series, Hoffer et al13 reported
are best understood within the context of lifetime TBI that 84% of mTBI veterans who had sustained a blast-
exposure.7 related mTBI had acute dizziness symptoms more than
mTBI is associated with a broad range of psychiatric 30 days after injury.13 A follow-up study in a smaller
and neurological symptoms, the most common of which cohort indicated persistent postural instability up to
are headache, fatigue, sleep disorder, dizziness, amnesia, 7 years later,14 a concerning finding, given that dizziness
information processing slowing, executive dysfunction, at just 6 months postonset is closely linked to psycho-
depression, and anxiety.8 mTBI sustained in combat is logical distress and failure to return to work.15
often accompanied by PTSD and bodily trauma, which A growing number of studies indicate that damage to
can make it difficult to determine the relative contribu- the vestibular system affects neuropsychiatric function
tion of each of these factors. Studies indicate that mTBI in a manner quite similar to that found in postcon-
is not by itself a strong determinant of well-being and cussive syndrome. In a seminal paper, Grimm et al16 re-
general functional outcome in veterans.9 Rather, it be- ported cognitive disturbances in patients diagnosed with
comes so when accompanied by comorbid neurological perilymph fistula syndrome including general forgetful-
and psychiatric complications. For example, Lippa et al9 ness, a specific deficit in auditory short-term memory,
found that while combat veterans with a history of mTBI apraxia, and a general slowing of information processing.
reported more psychiatric and behavioral conditions, Fatigue, anxiety, depression, and unexplainable dread
their disability (as measured by the World Health Orga- were also commonly observed and contributed to a clin-
nization Disability Assessment Schedule II [WHODAS ical picture that the authors described as functionally
2.0]) was not significantly affected. In contrast, Lippa devastating. More recent study has shown similar symp-
et al9 found that the concurrence of mTBI with PTSD toms in patients diagnosed with vestibular migraine and
and depression afforded a unique vulnerability to poor other nontraumatic pathologies,17 and a large-scale sur-
general outcome, causing a substantial worsening of in- vey of 20 950 adults in the United States revealed that
dependent function, self-care, and social reintegration. the 8% who self-reported vestibular vertigo were 8 times
Another common comorbidity in military mTBI is more likely to have serious difficulty concentrating or
vestibular impairment, although its effect on mental remembering, 4 times more likely to have limitations
health is less clear. The vestibular system comprises in daily living, and 3 times more likely to suffer from
peripheral organs located within the labyrinth of the depression, anxiety, or panic disorder.18
inner ear, which detect angular and linear acceleration Veterans who show balance impairment, either via
of the head. These organs convey information via the questionnaire19 or vestibulography,20 are also much
brainstem vestibular nuclei to cortical and subcortical re- more likely to report PTSD symptoms, a finding that
gions involved in sensorimotor control, interoception, may derive from the shared neurochemical features of
and spatial cognition. Although not as well character- the ascending vestibular afferent and limbic and arousal
Copyright © 2018 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.Vestibular Dysfunction Following mTBI 3
systems.21 This same network has also been impli- vestibular and psychiatric factors, which in studies of
cated in the strong association between balance impair- UK veterans has been hampered by the absence of stan-
ment and migraine headache.21 More recently, Hebert dardized vestibular and neurobehavioral measures.
et al20 reported high correlations in 30 veterans between Study recruitment was restricted to veterans actively
balance/postural impairment and self-reports of fatigue, seeking psychological support, given their poor life out-
depression, and PTSD. Together, these indicate that the comes and the higher likelihood of vestibular impair-
disturbances in gravitational and head-centered frames ment in individuals reporting psychiatric disturbance.
of reference induced by vestibular disorder compromise
brain processes involved in not only balance and auto- METHODS
nomic motor control but intellectual, emotional, inte-
roceptive, and arousal regulation too. Such indications Participants
raise the possibility that vestibular impairment makes an In total, 162 participants (158 white British, 4 black
independent contribution to the neurobehavioral and British) were recruited for study; see Table I for their
functional capacity of military veterans, regardless of demography and military background. One hundred
whether mTBI has been sustained. thirty-seven were recruited from a 6-week program of
The aims of the present study were 2-fold. First, we inpatient psychiatric treatment at one of 3 Combat Stress
sought to establish, for the first time, the relative preva- treatment centers in the United Kingdom, and 25 par-
lence of chronic vestibular injury in veterans with blunt, ticipants were recruited from drop-in counseling ses-
blast, or blunt + blast lifetime mTBI. Although each of sions at the Portsmouth Veterans Outreach Centre. Indi-
these mechanisms of injury can damage the vestibular viduals were eligible if older than 18 years, retired from
system, there is uncertainty over which, if any, show the the UK armed forces, and willing to consent to study
strongest association and thereby constitute the greatest participation. Potentially eligible participants were ap-
risk for vestibular-related impairment. By means of com- proached shortly after their treatment/counseling ses-
parison, studies of auditory dysfunction in military TBI sion and asked whether they would be willing to conduct
show a stronger association with blast injury; 62% and a survey aimed at assessing military veterans’ experience
38% of combat veterans who had sustained blast TBI re- of head injury. Favorable ethical opinions were given
ported hearing loss and reported tinnitus, respectively, prior to study commencement from the University of
whereas only 44% and 18% of veterans in the nonblast Kent School of Psychology and Combat Stress research
group reported hearing loss and tinnitus, respectively.22 ethics review panels.
The second, and most important, study aim was to con-
duct an exploratory investigation of the direct and indi-
Procedure
rect associations between vestibular symptoms and both
postconcussive symptoms and more general disability. Following written informed consent, participants
Statistical mediation analysis was applied to determine completed the survey in a quiet corner room accom-
whether postconcussive symptoms and more general panied by the experimenter. The survey comprised a
disability are linked with vestibular symptoms indepen- number of validated, standardized self-report assess-
dently of depression, anxiety, and PTSD, which have ments presented serially using the online survey software
also been shown to exert influence. Mediation analysis Qualtrics on an iPad. These assessments were adminis-
also made it possible to examine the interplay between tered in the order in which they appear in the following
TABLE 1 Sample demographic (N = 162)
n n or M (SD)
Male 151 Part-time student 2
Female 11 Unemployed 53
Relationship status Retired 32
Married 92 Military service branch
Divorced 39 Royal Navy 23
Single 29 Army 123
Widowed 2 Royal Air Force 11
Vocational status Royal Marines 6
Full-time employment 55 Armed service history
Part-time employment 19 Mean length of service, y 12.8 (7.2)
Full-time student 1 Mean deployments to a war zone 3.7 (1.8)
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Copyright © 2018 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.4 JOURNAL OF HEAD TRAUMA REHABILITATION
text and were preceded by questions about demographic fering from vestibular disturbance whereas those who
background and military service. Participants were told reported symptoms either never or only 1 to 3 times
that they could take breaks throughout the survey as per year were classified as not suffering from vestibular
needed. disturbance. Mediation analyses35 were conducted on
scores provided by those who self-endorsed mTBI to
Self-report measures determine whether the severity of their vestibular symp-
toms (as measured by the VSSL total score) indepen-
Participants’ lifetime history of TBI was measured dently contributed to the broad profile of postconcus-
using the Ohio State TBI Identification Method sive symptoms (as measured by the NSI and the HIT6)
(OSTIM).23 Additional questions were added from the and disability (WHODAS 2.0) when depression, anxi-
Boston Assessment of TBI-Lifetime (BAT-L) to deter- ety, and PTSD were taken into account as mediators.
mine blast proximity.24 Responses to the OSTIM de- The mediation analysis was also used to interrogate the
termined the presence/absence and severity of TBI us- relationship between vestibular symptoms and each of
ing the US Department of Defense and Department these mediators and between these mediators and each
of Veterans Affairs screening definitions.25 mTBI clas- of the outcome variables (NSI, HIT6, and WHODAS
sification involved an alteration of consciousness or 2.0). Finally, the analysis allowed us to assess the com-
mental state for a moment up to 24 hours postinjury bined association (ie, total effect) of the predictor and
and/or a loss of consciousness (LOC) of 0 to 30 min- mediator variables with the outcome measures.
utes and/or a presence of posttraumatic amnesia lasting Post hoc exploratory analysis interrogated the statis-
less than 1 day. Moderate TBI was defined by an LOC tical outcomes of the NSI mediation analysis. A sensi-
for more than 30 minutes and less than 24 hours. Se- tivity analysis was conducted in which the mediation
vere TBI was categorized as an LOC lasting more than analysis was rerun on the adjusted NSI total scores after
24 hours. Vestibular symptoms were assessed using the the 3 items (items 1-3) on the NSI that relate to imbal-
Vertigo Symptom Scale Long form (VSSL), which com- ance/unsteadiness were removed. This was carried out
prises 22 items that quantify the duration and sever- to determine whether the observed association partly
ity of vertigo and other dizziness symptoms.26 Current reflects the fact that both questionnaires probe several
postconcussive symptoms were mainly assessed using common symptoms. To estimate the extent to which
the Neurobehavioral Symptom Inventory (NSI),27 al- the observed relationship between VSSL and NSI scores
though the Headache Impact Test (HIT6)28 and Ep- reflects vertigo and balance factors as opposed to auto-
worth Sleepiness Scale (ESS)29 were also administered nomic and anxiety-related factors, 2 other modified ver-
to more comprehensively probe the predicted associa- sions of the original NSI mediation analysis were run;
tion between vestibular symptoms and headache and the first replaced the VSSL total score with the VSSL
daytime sleepiness. PTSD symptoms were assessed via vertigo-balance subdomain score, whereas the second re-
the PTSD Checklist for DSM-5 (PCL-5),30 and depres- placed the VSSL total score with the autonomic-anxiety
sion and anxiety were assessed using the Kessler Psycho- subdomain score.
logical Distress Scale (K10).31 Functional disability was Participants with missing data were excluded from
assessed using the World Health Organization Disabil- analysis. All inferential analyses were computed using
ity Assessment Schedule II short version (WHODAS SPSS 24.
2.0).32 Symptom exaggeration was assessed using the
Memory Complaints Inventory (MCI), which has been
validated in military personnel with a history of concus- Overview of sample characteristics
sion and in civilian populations presenting with anxiety See Table 1 for the sample demographic, Table 2 for
and depression.33,34 participants’ lifetime history and prevalence of mTBI,
and Table 3 for their comorbid neuropsychiatric symp-
RESULTS toms. The mean age of the group, which was mostly
male, was 46.6 years (standard deviation [SD] = 9.3)
Statistical analyses
and had been deployed to a war zone an average of 4
Summary statistics were calculated for the demo- times. Seventy-two percent of the sample reported a life-
graphic, TBI, and comorbid characteristics of the sam- time history of 1 or more mTBIs (mean age = 24.4, SD =
ple. Chi-square analyses were then applied to compare 10.52), 74% of which resulted in a visit to an A&E de-
the relative frequency of vestibular impairment in par- partment or acute military medical facility. Forty-nine
ticipants with self-endorsed blunt, blast, or blunt + blast percent reported that they had periods in their lives
(ie, both blunt and blast) mTBI. For the purpose of the where they had sustained repeated mTBIs. As shown in
χ 2 analysis, participants who reported dizziness symp- Table 3, the majority reported neurobehavioral and neu-
toms more than 3 times per year were classified as suf- ropsychiatric symptoms including imbalance, headache,
Copyright © 2018 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.Vestibular Dysfunction Following mTBI 5
TABLE 2 Lifetime history and prevalence of mTBI (N = 117)
n n
Lifetime history ≥1 mTBI 117 Blunt and blast 41
Blast-only 17
Hospitalized because of mTBI 82 Blunt-only 59
mTBI with LOC 69 Blast proximity
0-10 m 38
Sustained >1 TBI 112 11-25 m 15
Periods of repeated mTBIs 57 26-100 m 5
Method of blunt injury
History of moderate TBI 23 Road traffic 57
History of severe TBI 12 Sports-related 73
No TBI 10 Assault 54
Abbreviations: LOC, loss of consciousness; mTBI, mild traumatic brain injury; TBI, traumatic brain injury.
daytime sleepiness, PTSD, and depression/anxiety. The 53% of this subgroup reported 3 or more blast mTBIs.
average WHODAS score was 20.49 (SD = 10.70), which Of these blast mTBIs, 38 were sustained within a prox-
is worse than approximately 90% of the general inter- imity of 0 to 10 m, 15 within 11 to 25 m, and 5 within
national population.36 Seventy-three participants (50%) 26 to 100 m.
indicated that they drank alcohol regularly, consuming Forty-seven percent (n = 8) of participants in the blast-
a weekly average of 20.9 units (alcohol units defined by only category reported vestibular disturbance, 59% (n =
the UK Department of Health).37 Most of the sample 35) reported vestibular disturbance in the blunt-only cat-
(n = 118) had never used recreational drugs. Fifty-six of egory, and 83% (n = 34) reported vestibular disturbance
the 110 participants with 1 or more mTBIs who com- in the blunt and blast category. Chi-square analysis in-
pleted the MCI fell below the cutoff score (6 JOURNAL OF HEAD TRAUMA REHABILITATION
sample of 10 000 using 95% confidence intervals. Co- anxiety were strongly associated with outcome in all 3
efficients were considered statistically significant at mediation models (see b2 in figures), although PTSD
P < .05. Three mediation analyses were applied to deter- symptoms showed no significant influence (see b1 in
mine whether the severity of vestibular disturbance, as figures). While VSSL scores directly affected NSI scores,
defined by VSSL total score, imposed a direct effect on they showed no effect when combined with PTSD scores
postconcussive symptoms (NSI), headache (HIT6), and within the indirect pathway a1 ∗ b1 . In contrast, when
disability (WHODAS) independent of mediators PTSD combined with the depression and anxiety scores within
(PCL-5) and depression and anxiety (K10). the indirect a2 ∗ b2 pathway, VSSL scores were signifi-
As can be seen in Figure 1, the VSSL scores exerted cantly associated with NSI scores. Finally, there was a
a direct effect on the NSI (see Figure 1A), HIT6 (see significant total effect across all 3 mediation analyses,
Figure 1B), and WHODAS 2.0 (see Figure 1C) scores indicating that vestibular symptoms were significantly
independently of the psychiatric mediators in all 3 me- associated with outcomes both independently and in
diation models. There was also a significant association conjunction with the psychiatric mediators.
between VSSL score and the psychiatric mediators of de-
pression, anxiety (K10), and PTSD (PCL-5) (see a1 and Exploratory analysis
a2 pathways in figures). As expected, depression and
Sensitivity analysis indicated that both the direct and
indirect effects of VSSL scores on the NSI remained
significant after the 3 dizziness-related items on the NSI
were removed (see Table 4, part A.) Likewise, the pattern
of statistical significance remained unchanged when the
mediation analysis was rerun after replacing the VSSL
total scores with first the VSSL vertigo subdomain scores
and then the VSSL anxiety-related scores (see Table 4,
part B).
DISCUSSION
This is the first study to systematically assess whether
vestibular impairment, both directly and in conjunction
with psychiatric comorbidities, is associated with long-
term postconcussive symptoms and general disability in
military veterans reporting a lifetime history of mTBI.
Seventy-two percent of veterans reported 1 or more
mTBIs in their lifetime, a prevalence that is almost iden-
tical to the 71% lifetime estimate for US veterans7 but
higher than other UK estimates that have focused on
mTBI acquired during service or utilized less detailed
lifetime assessments. Approximately one-half of those
with mTBI reported periods in their life when they sus-
tained repeated injuries. The most frequent mechanism
of injury was blunt mTBI, mainly acquired during sports
activity and road traffic accident. Eighty-one percent of
the mTBI sample indicated they had been exposed to
blast, with 50% reporting mTBI as a consequence. Fifty-
three percent of this subgroup reported blast mTBI on
3 or more occasions, with approximately two-thirds oc-
curring within 10 m of the explosion, which is notable,
given that such close exposure has been associated with
decreased parietal-frontal connectivity.39 Three-fourths
Figure 1. (A) Mediation analysis NSI (N = 113). (B) Me-
of those who sustained mTBI visited either an A&E
diation analysis HIT6 (N = 112). (C) Mediation analysis
WHODAS (N = 111). NSI indicates Neurobehavioral Symp-
department or acute military medical facility. Over the
tom Inventory; HIT6, Headache Impact Test; WHODAS, longer-term, more than one-half of those who sustained
World Health Organization Disability Assessment Schedule mTBI reported persistent postconcussive neurobehav-
II short version; VSSL, Vertigo Symptom Scale Long form; ioral symptoms including dizziness, headache, and
and PCL-5, PTSD Checklist for DSM-5. daytime sleepiness, as well as depression, anxiety, and
Copyright © 2018 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.Vestibular Dysfunction Following mTBI 7
TABLE 4 Correlation matrices underpinning the exploratory NSI mediation analysis in
which (A) responses to the 3 dizziness questions were omitted and (B) responses to only
the vertigo-balance or autonomic-anxiety subdomains were included
Total Direct Indirect
effects effects Mediator effects LCI UCI
A. VSSL total score B = .50 B = .311 PCL-5 B = .055 − 0.016 0.130
P ≤ .001 P ≤ .001 Kessler B = .134 0.055 0.245
B. VSSL vertigo-balance B = .773 B = .540 PCL-5 B = .092 0.017 0.222
P ≤ .001 P ≤ .001 Kessler B = .139 0.015 0.343
VSSL autonomic-anxiety B = 1.129 B = .767 PCL-5 B = .100 − 0.109 0.287
P ≤ .001 P ≤ .001 Kessler B = .268 0.038 0.496
Abbreviations: Kessler, Kessler Psychological Distress Scale; NSI, Neurobehavioral Symptom Inventory; PCL-5, PTSD Checklist for
DSM-5; VSSL, Vertigo Symptom Scale Long form; PTSD, posttraumatic stress disorder.
PTSD. Alcohol consumption exceeded current UK gov- explain other aspects of postconcussion syndrome.
ernment guidelines of 14 units per week,37 and general Here, we confirm that when these comorbidities are con-
disability fell within the bottom 10% of the general in- trolled, vestibular impairment is separately associated
ternational population.36 Together, these data highlight with a range of mental competencies. A strong associ-
significant, long-term care needs in help-seeking UK mil- ation was found between the severity of self-reported
itary veterans with a self-reported history of mTBI. vestibular impairment and neurobehavioral symp-
Consistent with the high prevalence reported in other toms, as measured by the NSI, which contains items
military samples, 69% reported symptoms consistent that probe sensory perception, motor coordination,
with a chronic vestibular disturbance. To our knowl- sleep/fatigue, mood, and executive function. Additional
edge, this is the first study to determine whether the analyses showed that when psychiatric comorbidity was
likelihood of vestibular disturbance is influenced by taken into account, this strong association also held
the manner in which mTBI is acquired. Chi-square for both headache, an especially common symptom
analysis indicated that vestibular disturbance was most of mTBI, and general disability as measured by the
commonly experienced following blunt and blast in- WHODAS 2.0, which encompasses activities of daily
jury combined rather than by only blunt or blast; living and social interaction. Interestingly, these direct
83% of blunt + blast mTBIs reported vestibular distur- effects of vestibular impairment on postconcussive
bance compared with 47% and 59% for blast and blunt symptoms and general disability held when scores from
mTBIs, respectively. This finding contrasts with the pre- only the vertigo subdomain of the VSSL were entered
dominance of blast injury in soldiers with auditory im- into the mediation analysis. This result gives support to
pairment and may partly reflect the insulation afforded the idea that the primary vestibular deficit (as opposed
by the deep-lying, bony labyrinth to external pressure to vestibular-induced psychiatric deficits, which can
waves. Although it is unclear how much the vestibular be difficult to disentangle from psychiatric deficits of
impairment sustained by blunt and blast injury reflects alternative origin) contributed to the direct effects.
peripheral as opposed to central nervous damage, its In addition to uncovering a direct link between
high prevalence suggests that this blunt and blast group vestibular and postconcussive symptoms, the mediation
should be considered most at risk for vestibular-related analysis uncovered an indirect link that incorporated co-
complaints for many years postinjury. morbid psychiatric disturbance. Previous study tells us
It has been known for some time that comorbid psy- that vestibular disorder can promote psychiatric distur-
chiatric symptoms of depression and anxiety exacerbate bance, so it is perhaps unsurprising that this pathway
postconcussive symptoms.9,40 The current data are the was also linked to outcome. However, the relationship
first to endorse these deleterious effects in a UK military between psychiatric and vestibular functions is partly
mTBI sample, and likely only fail to do so for PTSD reciprocal, which makes it difficult to reach strong in-
because most participants reported significant PTSD ferences about causality, a problem deepened by the
symptoms, so together produced too little variability for fact that many military veterans with mTBI present with
the correlation to reach statistical significance. But while psychiatric complaints that are partly nonvestibular in
all previous studies have identified dizziness/imbalance origin. Some insight can be gleaned from the significant
as a common postconcussive symptom, they have direct effects of the VSSL autonomic-anxiety subdomain
overlooked the fact that the vestibular impairment may on outcome, which suggest that, at the very least, the
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vestibular disturbance was exacerbating symptoms of a and other postconcussive symptoms can be conflated by
psychosomatic and somatopsychic nature. clinically naive participants. Also, the study was cross-
Reflecting more broadly on the clinical presenta- sectional rather than longitudinal, and all participants
tion of the present study sample, the constellation of were help-seeking and receiving psychiatric support, so,
vestibular, cognitive, and affective symptoms mirrors although high in clinical need, were not representative
the general neuropsychiatric profile of civilians with di- of the broader veteran population. To this end, it would
agnosed vestibular impairment but without a history be informative to address the current study questions
of mTBI.16,17 It further demonstrates the pervasive in- in a participant sample with more varied mental health
fluence of the vestibular system on human cognition,17 needs. On a related note, the high prevalence of depres-
affecting higher-level processes rather than only the low- sion in the sample may help explain the relatively high
level autonomic motor control processes with which number of MCI failures, which is of potential concern
it has traditionally been associated. From a therapeu- here because symptom exaggeration in one neurological
tic perspective, the implication is that veterans with modality predicts exaggeration in other modalities.43–46
mTBI might broadly benefit from a program of vestibu- Given that this study is the first to assess symptom ex-
lar rehabilitation. In preliminary support of this idea, aggeration in UK veterans, this result should perhaps
Kleffelgaard et al41 showed in a case series of 3 civil- be treated cautiously, not least because the study design
ians with mTBI and dizziness/imbalance that a program does not allow the underlying drivers of malingering
of vestibular rehabilitation was associated with reduced and psychological dissociation to be separated. But for
psychological distress and improved health-related qual- the present purpose, it is important to point out that the
ity of life. In veterans, Carric et al42 showed a reduc- statistical outcomes from the mediation analyses are the
tion in PTSD, as measured by the clinician-administered same if only those participants who passed the MCI are
PTSD scale, after 2 weeks of vestibular-ocular coordi- included.
nation involving gaze stabilization, visual pursuit, and
saccadic eye movement. Carric et al42 also noted that CONCLUSION
treating PTSD as a physical injury rather than as a psy- In conclusion, we report preliminary evidence that the
chiatric disorder helped lessen the stigma that veterans long-term mental health of help-seeking military veter-
often feel toward help-seeking, which, in turn, could ans with mTBI is directly associated with the presence
encourage treatment uptake. of vestibular dysfunction. This finding is important be-
Several methodological aspects limit the conclusions cause, although anecdotal reports of dizziness are com-
that can be drawn from the current study. First and mon, vestibular function is not routinely assessed and,
foremost, the absence of routine prospective screening as a consequence, neuro-otological referrals are not of-
for mTBI and vestibular disorder meant that our inves- ten made. Yet, the current data raise the possibility that
tigations were founded on self-report data rather than by treating the vestibular disorder, it may also be possi-
clinical examination, which may have led to an overes- ble to treat a range of neurobehavioral symptoms that
timation of effect. This overestimation may have been accompany mTBI and which have so far proven difficult
exacerbated by the relative ease with which vestibular to manage.
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