Vestibular Assessment in Patients with Persistent Symptoms of Mild Traumatic Brain Injury

Abstract

Aim

The estimated worldwide incidence of TBI is 10 million cases per year. Dizziness and imbalance are two common symptoms in mild TBI (mTBI). In about 10–15% of TBI patients, these symptoms remain for a long time and may show no recovery. These persistent symptoms may relate to different factors including vestibular abnormalities. The aim of this study is a vestibular assessment of patients with persistent symptoms of mTBI by different tests including computerized dynamic posturography.

Materials and Methods

21 patients with mTBI evaluated in this study. Patients were civilians with persistent symptoms. TBI did cause by blunt force trauma (mainly from falling) in the past 6 months. They had normal neurologic and musculoskeletal assessments and no temporal bone fracture. Several auditory and vestibular evaluations were performed for each patient. They included: case history, otoscopy, pure tone and speech audiometry, tympanometry, vestibular bedside examination (spontaneous nystagmus, gaze, saccade, pursuit, Dix–Hallpike maneuver, side-lying maneuver, roll, and Romberg test), cervical Vestibular Myogenic Evoked Potential (c-VEMP), Computerized Dynamic Posturography (CDP) and Dizziness Handicap Inventory (DHI).

Results

Patients showed hearing loss in 10 (47.6%) and tinnitus in 4 (19.0%) cases. In ocular motor tests, patients had the most abnormal results in the pursuit test. 6 patients also had Benign Paroxysmal Positional Vertigo (BPPV) in the posterior canal. c-VEMP showed abnormal saccular function in 14 patients. In CDP, the composite scores were decreased relative to normal populations.

Conclusion

vestibular tests showed abnormal results in most patients. Vestibular abnormality could relate to persisting symptoms of mTBI patients.

Introduction

Traumatic Brain Injury (TBI) is common. The incidence of TBI in the US is 150–500 in 100,000 individuals [1]. The estimated worldwide incidence of TBI is 10 million cases per year [2]. Most cases (76–83%) of TBI are mild TBI (mTBI) [2, 3]. mTBI exists in both civilians and military service members. Also, the incidence of mTBI is probably underreported because of different factors such as poor documentation [2].

Headache and dizziness are common symptoms in TBI patients [3–5]. Dizziness is the most common symptom after headache [6]. Headache also could be related to other symptoms such as imbalance. It was reported that mTBI patients with headaches also have more imbalance [7]. The Imbalance is also very common symptoms in TBI patients [3–5, 8, 9]. In general, trauma may involve multisystem such as vestibular, visual and central nervous systems with different severity. It could greatly affect balance function [10].

After head trauma, many patients have dizziness but their description of symptoms is vague and unclear [2, 11]. Many of these patients would recover quickly but in some cases, symptoms may remain for a long time [11]. About 10–15% of patients would have persistent symptoms that may exist even years after trauma [12]. Prevalence of Persistent symptoms in patients with mild TBI could be high as one-third of TBI patients in 4 [9] and 5 [13] years follow-ups. The prevalence of persistent symptoms also could be up to 48% in military service members with TBI [2].

The usual symptoms of TBI would appear in mTBI cases. 24–83% of patients with mTBI have dizziness or imbalance [14]. In another study, the imbalance is reported in about 27–52% of mTBI patients [15].

The persistent symptoms of TBI may not greatly relate to the trauma mechanism. TBI may cause by a blast or blunt force trauma. However, there is no significant difference in the rate of reported symptoms in the blast and non-blast TBI at least in military members [16]. However, some factors including vestibular abnormality may relate to persistent symptoms. The function of the vestibular system and especially the saccular system has a great role in holding balance and especially standing. An abnormal saccular function may interfere with standing position and cause imbalance. There are different tests for evaluating vestibular function. Cervical Vestibular Myogenic Evoked Potential (c-VEMP) evaluates the saccular system. This test in addition to Computerized Dynamic Posturography (CDP) could evaluate imbalance in TBI patients. Subjective questionnaires such as Dizziness Handicap Inventory (DHI) also could be very helpful for the evaluation of self-perceived problems and handicapping of patients.

The aim of this study is the vestibular assessment of patients with persistent symptoms of mTBI by different vestibular tests.

Materials and Methods

Participants

This is a prospective cross-sectional study. The patients with mTBI evaluated in this study. The patients were classified as mTBI if they had the following criteria: 1-Glasgow Coma Scale (GCS) of 13–15 at admission. 2-Loss of consciousness lower than 30 min. 3-Normal imaging if requested. They were selected from XXXX hospital by a simple random sampling method. Inclusion criteria were 1-patients (civilians) with blunt force trauma in the past 6 months, 2-age of 18–60 years old, 3-no history of hearing loss, vertigo, imbalance or gait abnormality before trauma, 4-persistent vertigo or imbalance after trauma, 5-Normal neurologic and musculoskeletal assessments, 6-No temporal bone fracture. Exclusion criteria were included; 1-having conductive or mixed hearing loss (for correct evaluation of patients with air conduction c-VEMP) or 2-neck or eye abnormality. All participants were informed consent for participation in this study. Study was according to code of ethics for human experiments (declaration of Helsinki). This study accepted by the Ethics Committee of local University of Medical Sciences (project number: 91/d/130/3430).

Procedure

First, a neurosurgery specialist performed a neurologic evaluation. Patients had normal neurologic and musculoskeletal assessments. They also had a normal CT scan and MRI if requested. Second, they referred to an otolaryngology and audiology clinic for further evaluations.

Several auditory and vestibular evaluations were performed for each patient. They included: case history, otoscopy, pure tone and speech audiometry, tympanometry, vestibular bedside examination (spontaneous nystagmus, gaze, saccade, pursuit, Dix–Hallpike maneuver, side-lying maneuver, roll, and Romberg test), c-VEMP, CDP and DHI. All of the tests performed by a trained audiologist in auditory and vestibular evaluations (first author).

Pure tone and speech audiometry (Maico, Germany) was performed in sound treated-room and by a calibrated audiometer.

In vestibular bedside examination, Gaze and saccade were performed in horizontal and vertical planes. In the Dix–Hallpike maneuver, the examiner stood behind patients. Patients turn their heads to one side and then lied down with head placing out of bed and stretching toward earth. Maneuver repeated for another side. In Romberg’s test, the ability to maintain balance in standing position was evaluated with open and close eyes.

c-VEMP (Labat, Italy) measured from the ipsilateral sternocleidomastoid (SCM) muscle. Patients controlled the tonic contraction of SCM with a feedback method. Patients were asked to turn head to the opposite side and maintain constant pressure on a cushion placed under their chin. The stimulus was 500 Hz tone bursts that presented via headphones at 5 times/s. electrodes placed at the forehead (ground), middle of SCM (+) and upper sternum (–). The impedance was lower than 3 kΩ.

DHI was used for the evaluation of patients’ self-perceived handicapping. It is a well-known questionnaire that evaluates the physical, emotional, and functional aspects of vertigo and imbalance. DHI has high validity and reliability. It has 25 items that could be answered with no (0 points), sometimes (2 points) and yes (4 points). Total scores of 0–14, 16–26, 28–44 and 46–100 show no self-reported handicapping, mild, moderate and severe self-reported handicapping, respectively.

CDP (Equitest, USA) was included Sensory Organization Test (SOT) and Motor Control Test (MCT). SOT performed barefoot at six positions: 1-standing with open eyes, fixed visual environments, and surface. 2-Closed eyes and fixed surface. 3-Open eyes and sway referenced visual environments. 4-Open eyes and sway referenced surface. 5-Closed eyes and sway referenced surface. 6-Open eyes, sway referenced visual environments and surface.

MCT was also performed barefoot for small, medium and large perturbations and MCT composite scores were calculated. Three trials performed for each condition in SOT and MCT. Results compared to age-matched data of normal populations.

Data Analysis

SPSS version 19.0 was used for analysis. Descriptive analysis performed for demographic factors. The normality of data was evaluated by Kolmogorov–Smirnov test. The Independent t test performed for comparing the results of patients with normal and abnormal saccular functions. Fisher exact test was used for comparing the qualitative data. p values lower than 0.05 considered statistically significant.

Results

21 patients evaluated in this study. The data had normal distributions. Patients were 45.0 ± 12.7 years old. 20 out of 21 were male. All patients had blunt force trauma that caused mainly from falling. 16 patients had trauma to temporal-parietal area and 5 patients to occipital area of skull. Patients had normal otoscopy in the first examination after trauma. Hearing and vestibular assessment performed in a single day in 118.2 ± 52.5 days after trauma. Some patients complained about vertigo (n = 21, 100.0%), imbalance (n = 14, 66.6%), hearing loss (n = 9, 42.8%) and tinnitus (n = 4, 19.0%).

Hearing Assessment

In hearing assessment, 18 out of 21 patients showed a hearing loss. None of patients had a history of hearing loss before trauma. However, 8 patients had expected hearing loss based on their age. Therefore, at least trauma caused hearing loss in 10 out of 21 (47.6%) of patients. Hearing loss ranged from mild high frequency to bilateral profound sensorineural hearing loss (SNHL). Symmetrical SNHL observed in most cases and only 4 (19.0%) patients had unilateral or asymmetrical SNHL. Tympanometry was normal (type A) in all ears. 4 (19.0%) patients also had tinnitus. The amount of hearing loss was different in these patients. One patient had profound sensorineural hearing loss and the others had mild and moderate hearing loss. In 2 (9.5%) cases, tinnitus was bilateral.

Vestibular Bedside Examination

Abnormal results in spontaneous nystagmus, gaze, saccade, and pursuit tests were observed in 0 (0.0%), 4 (19.0%), 0 (0.0%) and 8 (38.0%) patients, respectively. Dix–Hallpike maneuver, side-lying maneuver, and roll test showed Benign Paroxysmal Positional Vertigo (BPPV) in 6 (28.5%) patients. All of these patients had BPPV in posterior canals. Only one case had bilateral BPPV. Romberg test was normal in all patients.

c-VEMP Results

The abnormal saccular function was observed in 14 (66.6%) patients. 6 out of 14 cases showed bilateral saccular abnormality. Abnormal results in c-VEMP were included absent waves and more than 35% amplitude asymmetry in the amplitude of P13-N23. Patients divided based on c-VEMP into two groups labeled as normal and abnormal saccular functions.

CDP Results

The results of CDP were compared in TBI patients with normal and abnormal saccular function (Table 1).

Table 1.

Abnormal results of CDP in patients with mTBI with normal and abnormal saccular function

	All patients (n = 21)	Patients with normal saccular function (n = 7)	Patients with abnormal saccular function (n = 14)
Abnormal SOT
Somatosensory	1 (4.76%)	0 (0.00%)	1 (7.14%)
Visual	4 (19.05%)	1 (14.29%)	3 (21.43%)
Vestibular	7 (33.33%)	2 (28.57%)	5 (35.71%)
Preference	6 (28.57%)	2 (28.57%)	4 (28.57%)
Strategy	9 (42.86%)	3 (42.86%)	6 (42.86%)
COG	6 (28.57%)	1 (14.29%)	5 (35.71%)
Overall SOT	11 (52.38%)	3 (42.86%)	8 (57.14%)
SOT composite score	69.2 ± 11.1	71.29 ± 10.81	68.29 ± 11.53
Abnormal MCT
Overall MCT	0 (0.00%)	0 (0.00%)	0 (0.00%)
MCT composite score	110.9 ± 53.8	93.50 ± 72.71	120.45 ± 41.37

*Fisher exact test was significant. p < 0.05

** Independent t test was significant. p < 0.05

Independent t-test also didn’t show any significant difference for SOT and MCT composite score between two groups (p > 0.05).

DHI Scores

DHI scores calculated for all patients. The DHI scores of patients showed in Table 2.

Table 2.

The DHI scores in patients with TBI

	All patients (n = 21)	Patients with normal saccular function (n = 7)	Patients with abnormal saccular function (n = 14)
Functional	15.3 ± 9.1	10.29 ± 6.87	18.00 ± 9.27
Emotional	10.7 ± 8.9	7.71 ± 5.70	12.31 ± 10.16
Physical	11.0 ± 9.5	8.86 ± 7.47	12.15 ± 10.59
Total score	37.0 ± 24.9	26.86 ± 18.50	42.46 ± 26.93

*Independent t test was significant. p < 0.05

Independent t-test performed between two groups of normal and abnormal saccular functions. The difference between the two groups was not significant (p > 0.05).

Pearson correlation coefficient showed a significant relationship among DHI total scores and SOT composite scores (r: − 0.579). This relationship also existed among all of the subgroups of DHI and SOT composite scores. However, there was no relationship among DHI scores with MCT scores except for the emotional subgroup (r: − 0.488).

Balance Abnormalities in Patients with BPPV

5 out of 6 patients with BPPV also had an abnormal saccular function. MCT composite score, functional, emotional, physical and total DHI score didn’t have a significant difference in patients with and without BPPV (p value > 0.05). However, SOT composite score was lower (61.1 ± 12.6 versus 72.5 ± 8.9) in patients with BPPV (p value = 0.030).

Abnormal Results in Patients with Imbalance

All of the patients had vertigo but 14 (66.6%) patients had an imbalance. Table 3 compared the different test results in patients with and without imbalance.

Table 3.

Abnormal results in patients with and without perceived imbalance

	All patients (n = 21)	Patients without imbalance (n = 7)	Patients with imbalance (n = 14)
BPPV	6 (28.57%)	1 (14.29%)	5 (35.71%)
Abnormal c-VEMP	14 (66.67%)	5 (71.43%)	9 (64.29%)
Abnormal SOT
Somatosensory	1 (4.76%)	0 (0.00%)	1 (7.14%)
Visual	4 (19.05%)	1 (14.29%)	3 (21.43%)
Vestibular	7 (33.33%)	2 (28.57%)	5 (35.71%)
Preference	6 (28.57%)	1 (14.29%)	5 (35.71%)
Strategy	9 (42.86%)	1 (14.29%)	8 (57.14%)
COG	6 (28.57%)	1 (14.29%)	5 (35.71%)
Overall SOT	11 (52.38%)	3 (42.86%)	8 (57.14%)
SOT composite score	69.2 ± 11.1	74.57 ± 8.48	66.64 ± 11.59
Abnormal MCT
Overall MCT	0 (0.00%)	0 (0.00%)	0 (0.00%)
MCT composite score	110.9 ± 53.8	116.83 ± 57.7	107.73 ± 54.19

*Fisher exact test was significant. p < 0.05

** Independent t test was significant. p < 0.05

The DHI scores, SOT and MCT composite scores didn’t have a significant difference between the two groups of patients with and without imbalance (p > 0.05).

Discussion

In this study, we evaluated the vestibular system in patients with persistent symptoms of mTBI. Patients had dizziness and imbalance after trauma. They also showed hearing loss, saccular abnormality and loss of balance function in the vestibular evaluations. Generally, dizziness and imbalance of mTBI patients may relate to many factors including vestibular abnormalities [17]. Trauma may affect vestibular systems and cause different vestibular abnormalities [18]. We found vestibular abnormality in most of our patients. The prevalence of vestibular abnormality could be high as 30–65% in TBI [10] and up to 71% in mTBI patients [19]. There is no significant difference in vestibular abnormalities for blast or non-blast TBI [16] and don’t have a relationship to trauma mechanism [18].

Hearing Assessments

Trauma may cause conductive, sensorineural or mixed hearing loss [10]. We observed a hearing loss in 10 (47.6%) of our patients. Damage to the auditory system is observed in many studies [6, 16]. It was reported in 33–49% of TBI patients [10, 20] in both acute and chronic stages of TBI [21]. Trauma would damage different sites of the auditory system such as tympanic membrane and hair cells [22]. Patients have different symptoms such as tinnitus, hearing loss and otalgia [15]. Patients with more severe extremity damages are more susceptible to having hearing loss or tympanic membrane perforation [23]. It also seems blast TBI have more chance of auditory damage relative to non-blast TBI (odds ratio = 1.45–2.076) [16]. Some of our cases with saccular abnormality had hearing loss. However, the presence of hearing loss usually had no relation with otolith abnormality [24].

The tinnitus could also be prevalent and many TBI patients could have tinnitus. We observed tinnitus in 4 (19.0%) patients. However, in one study 42% of TBI patients had tinnitus [25].

Vestibular Bedside Examination

In the vestibular bedside examination, 4 (19.0%) patients had abnormal results in the gaze test. They showed horizontal nystagmus. It indicates a peripheral vestibular abnormality in TBI patients [12]. Usually, TBI patients have normal results in the gaze test [3]. gaze test also is not very sensitive in TBI patients [3].

8 (38.0%) patients had abnormal results in pursuit. It was reported that the incidence of abnormal pursuit results is higher than other ocular motor tests in TBI patients [3]. Other studies also showed similar results but in one study, the abnormal results were more in vertical rather than horizontal planes [3]. Generally, abnormal results in the Ocular motor test would found in less than 8% of patients with dizziness after mTBI [15]. It also reported that in trauma cases without temporal bone fracture, the peripheral vestibular system usually would damage [17], this finding supports a low rate of abnormal results in ocular motor tests. Because they usually are abnormal in central lesions.

BPPV

BPPV was observed in 6 (28.5%) patients. Most of them also had an imbalance. BPPV is frequent after trauma [15, 24, 26]. It is the most common reason for dizziness in TBI patients [17]. It is observed in 10–25% of TBI patients [14] or 5–57% of mTBI patients with dizziness [15].

BPPV resulted from mTBI would cause more severe symptoms, It has poorer prognosis and higher recurrence rate [17]. The high prevalence of BPPV also indicate that otolith abnormality is common in these patients [14].

The Balance Function of Patients with TBI

Balance is a complex concept and it relies on interactions of vestibular, visual and somatosensory systems. Sensory integration of sensory systems is essential for holding balance especially for standing and walking [19]. Imbalance in TBI patients also may relate to sensory integrations [13]. CDP could evaluate and quantify the balance and interactions among different sensory systems [26]. CDP is an objective assessment of balance function. Usually, other clinical assessments of standing function in TBI patients have poor reliability. Therefore in some studies, Using CDP is recommended in the evaluation of TBI patients [9].

TBI patients show different balance abnormalities including lower SOT composite scores, lower ability to use the vestibular cue, higher reliance on visual inputs for holding balance [9, 12, 26–29], more imbalance in the absence of correct visual information [15] and the inability of using sensory inputs for holding balance [30]. They also tend to sway more than normal people [12, 26] in anterior/posterior and lateral [28] directions. Abnormal CDP results even reported in children with mTBI [31]. However, motor abnormalities may be less frequent than sensory abnormalities in TBI patients [25] and Visual vestibular mismatch in TBI patients may not affect CDP [32].

In our patients, SOT composite scores were decreased relative to normal populations. Other studies also showed similar results in TBI patients [10, 26, 27]. The imbalance is a very common symptom in TBI patients [8, 20] and mTBI patients show an imbalance in CDP [7, 19]. Some aspects of our patients’ persisting symptoms may relate to time passed since the trauma. It was suggested that time from trauma may affect the balance function [19]. Although, we didn’t find a significant correlation between time to evaluation day and SOT and MCT composite score. (Data was not shown.) Some of TBI patients may improve over time but imbalance may never improve in some other patients. In some patients with chronic TBI, imbalance could worsen over time [20], especially in some untreated TBI patients [21]. The prevalence of vertigo is also higher in the chronic stage [20]. The results of CDP (SOT and MCT) also may worsen in 3 months relative to 3 days after trauma [25].

Vestibular abnormality plays an important role in the balance of TBI patients [6]. This also may relate to the persisting symptoms of our patients. TBI patients usually had more trouble in using vestibular cue for holding balance [7, 28] and the vestibular system may be the main source of imbalance in some TBI patients [28]. vestibular results also show more damaged than other aspects of CDP in mTBI patients [7].

CDP is very helpful for quantifying patients’ problems. CDP showed to be successful in identifying vestibular abnormality from healthy controls or malingering balance abnormality [33]. However, it cannot separate the effect of TBI and non-head damages such as neck problems [29]. Neck problems are also common among trauma patients. Neck trauma also causes postural instability and lower CDP scores [34]. However, we excluded all the patients with neck problems.

The imbalance in TBI patients must be treated and Vestibular rehabilitation could help TBI patients with vestibular abnormality [10, 35], vestibular rehabilitation with virtual reality also may help TBI patients with vestibular abnormality to have better gait [36].

Otolith Abnormality

Trauma may damage the vestibular system and especially the otolith system. It damages the end organs and vestibular nerve [17, 28], even in patients without temporal bone fracture [17]. In our patients, the additional saccular abnormality or even perceiving imbalance didn’t significantly change SOT and MCT composite scores. Similar results were found in another study [37]. In that study, composite SOT and MCT scores didn’t show any difference between symptomatic (including imbalance) and asymptomatic TBI patients. However, conditions 5 and 6 in the symptomatic patients had lower scores and these vestibular conditions showed higher incident of vestibular abnormality in symptomatic patients [37]. It was reported that CDP and specially SOT are a relatively sensitive test for otolith abnormality in head trauma patients [38]. However, this test may be not sensitive enough for detecting all patients with otolith abnormality. Even if both organs of utricle and saccule damage, the sensitivity of CDP would only reach to 50%, it shows the sensitivity of CDP for evaluating these patients are relatively poor [39]. Also, the specificity and cost-effectiveness of CDP are controversial [39].

The otolith system has a main effect on postural stability. It provides important information on balance in different situations such as standing. Otolith abnormality may cause different symptoms such as imbalance, diplopia, and sensation of falling [40]. In particular, the saccular abnormality would cause imbalance [40]. Otolith abnormality also can cause dizziness and vertigo [24]. Otolith abnormalities may result in more sway and falling in TBI patients [15]. Dizziness of otolith abnormality in TBI patients is perceived as tilt or pushing and pulling sensations [15]. otolith abnormality may have a great role in the imbalance of TBI patients [14]. Otolith abnormality in mTBI patients would cause damaging postural control and could result in more trunk sway relative to healthy control groups [39]. otolith abnormalities may be the main cause of CDP abnormalities in head trauma patients [41].

Abnormal otolith functions were found in many TBI patients [15, 18, 24]. It seems otolith organs are susceptible to damage in trauma [14]. It also seems otolith abnormalities are even more frequent than semicircular abnormality [15]. Otolith organs would damage more frequently in linear acceleration trauma [6]. Linear acceleration trauma also more frequently result in TBI [6]. Therefore, many cases of TBI may also have undetected otolith abnormalities.

The otolith abnormalities also were observed in the blast [15] and blast-wave incidents [22].

Also in blast trauma, the otolith system is susceptible to damage [15] and even more susceptible than semicircular canals [30]. The otolith abnormality is also more frequent than semicircular canals abnormality [15, 30]. The otolith receptors are more vulnerable to pressure [15].

Psychological Aspects of Persisting Symptoms

TBI patients with vestibular abnormalities may show different symptoms such as dizziness, imbalance, and oscillopsia [10]. Dizziness is very common in TBI patients and up to 81% of patients showed dizziness in the first days and 3 months after trauma [25]. Most cases of dizziness after TBI would resolve gradually but these symptoms also could get worse [15]. The dizziness also would result in decreasing quality of life, daily activity and psychological health [17]. In TBI patients with persistent symptoms, self-reported balance problems and the patients’ symptoms could have little change over time [9].

A few studies evaluated the relationship among self-reported problems, TBI symptoms and test results [9]. Our patients showed higher scores in DHI relative to the normal population but having an imbalance or saccular abnormality didn’t significantly increase DHI scores. Similar results were reported for non-trauma causes of vestibular abnormality. In these patients, Additional otolith abnormality also causes no extra severity to report symptoms or self-perceived handicapping [40].

There are a relationship between CDP and patients’ symptoms [25, 27], especially between the physical subgroup of DHI with SOT [19, 27]. We also found a relationship between DHI scores and SOT composite scores.

DHI is a valuable tool for evaluating patients’ views about dizziness and imbalance. It could also show progress or worsening of symptoms. Other studies also showed the effects of vertigo and imbalance in TBI patients on DHI scores [21, 26, 27, 37]. However, DHI scores may relate to other aspects of TBI, beside vestibular abnormalities. Psychological issues such as stress, anxiety, depression, and PTSD also could affect DHI scores. In military members with TBI resulting from blast exposure, imbalance and vestibular abnormality are common [36]. It affects auditory, peripheral and central vestibular system [22]. It also affects the daily living of patients and decreases their quality of life. They also may suffer from PTSD or depression that could influence the subjective measurements such as DHI [14]. In these cases, objective measurements such as CDP could be useful. Many cases of mTBI especially military cases may also suffer from psychological issues [2, 16] however, the nature of trauma may don’t affect the psychological factors [16].

Persisting dizziness also may relate to different Psychological factors. Psychological issues such as stress, anxiety, depression, and PTSD also play an important role [42]. These factors may affect patients’ perceived handicapping and DHI scores. However, our patients were civilians and none of them had any apparent Psychological issue. But, we could not rule out the Psychological effects of TBI on our patients.

The Study Limitations

The lack of a control group is our main limitation. Comparing these results with a control group can improve the study design. The other limitation is the variable time between trauma and hearing and vestibular evaluation. Although, all patients were evaluated in the chronic stage of mTBI.

Conclusion

Vestibular tests showed abnormal results in these patients. The vestibular abnormality may participate in persisting symptoms of mTBI patients.

Compliance with Ethical Standards

Conflict of interest

The authors had no conflict of interest.

Human and Animals Rights

All procedures performed in study involving human participant were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed Consent

Informed consent was obtained from all individual participants included in the study. This study accepted by the Ethics Committee of Tehran University of Medical Sciences (Project Number: 91/d/130/3430).