Auditory Dysfunction in Non-blast-related TBI: A Guide for Audiologists

Traumatic brain injury (TBI), one of the leading causes of morbidity and mortality, constitutes considerable health and socioeconomic burden.1-5 In 2007, Hyder, et al.,6 estimated that TBI would affect 10 million people globally by 2020, a substantially smaller proportion compared to the recent estimate of 50 million people.7 The increasing global prevalence of TBI2 calls for a rising need to emphasize the importance of its progressive and long-term consequences, including post-traumatic hearing deficits during both the acute and chronic stages of injury.Shutterstock/S K ChavanFigure 1: Case history taking recommendations. Abbreviations: Motor Vehicle Accident (MVA); Computed Tomography (CT); Magnetic Resonance Imaging (MRI); Patient Reported Outcome Measures (PROMS); Hearing Handicap Inventory for Adults (HHIE); Tinnitus Handicap Inventory (THI), Hyperacusis Questionnaire. Hearing loss, brain injury, audiology.Figure 2: Recommended assessment procedure for patients with post-traumatic hearing loss. Abbreviations: Patient Reported Outcome Measures (PROMS); Hearing in Noise Test (HINT); Quick Speech in Noise (Quick-SIN); Auditory Brainstem Response (ABR). Hearing loss, brain injury, audiology.The manifestation of progressive and long-term consequences of non-blast-related TBI depends on the severity of the injury and includes a wide variety of symptoms impacting the physical (i.e., fatigue, loss of coordination, speech production, headache), cognitive (i.e., amnesia, irritability, depression), and sensory (i.e., blurred vision, hearing/tinnitus, vertigo) systems.3, 8 The typical auditory and vestibular symptoms secondary to TBI can stem from injury to the central and/or peripheral pathways. In auditory dysfunction, damage to either outer and/or middle ear results in a conductive hearing loss (CHL), inner ear and auditory nerve in a sensorineural hearing loss (SNHL), and damage to both conductive and sensorineural regions results in a mixed loss. Regardless of the severity of TBI, SNHL is the most prevalent, 9-11 particularly that of high-frequency SNHL.12 From a vestibular dysfunction point of view, damage to sensory organs (i.e., otolithic organs and semicircular canals) results in postural instability and vertigo, respectively,13 with posterior semicircular canal benign paroxysmal positional vertigo (BPPV) as the most prevalent vestibular deficit.14 The manifestation and effects of post-traumatic impairments can further combine in complex ways, hindering the identification of hearing loss. For instance, the presence of cognitive deficits, especially memory disturbance and poor self-awareness, may reduce the patients’ insight into any changes to their hearing while physical deficits (i.e., loss of coordination) may substantially reduce their ability to attend appointments with a health care provider.15 Information is scarce on the prevalence, nature, and severity of peripheral hearing loss, recovery patterns, and effects of non-blast-related post-traumatic hearing loss on patients’ lived experiences. The absence of such knowledge carries substantial implications particularly from the clinical practice point of view and can affect adequate diagnosis through a lack of an appropriate triage process, evidence-based choice of test battery, and ultimately the provision of evidence-based rehabilitation. Professional organizations such as the American Speech and Language Association16 are becoming increasingly aware of considerations relating to audiological and vestibular assessments following TBI as the availability of related research improves, particularly in that of military and/or veteran personnel following blast-related TBI. Clinical practice guidelines for mild TBI have been developed17, 18 to guide and assist health care professionals, including audiologists, in the assessment and management of patients’ persistent symptoms following TBI. Given the overlap of symptoms with other clinical disorders, guidelines targeting a group of health care professionals rather than an individual discipline is very appropriate in this instance. It is further important to note that there is some international variability across developed nations in recommendations on the assessment and management of hearing loss post non-blast related TBI, with some countries (i.e., Canada) much further advanced than others (i.e., Australia), as demonstrated by the Canadian Guidelines for Mild TBI.18 In this paper, we provide further insights, specific to the profession of audiology, into the effects of non-blast-related TBI on hearing and provide preliminary recommendations for the identification of hearing loss in this patient population. AUDITORY PATHOLOGY SECONDARY TO TBI Auditory system-related deficits resulting from TBI stem from injury to the auditory periphery and/or the central auditory system pathways. Auditory periphery deficits, the focus of our investigation, involve either damage to the outer, middle, inner ear, and/or auditory nerve structures. Literature and clinical evidence exploring the effects of TBI on auditory dysfunction increasingly supports SNHL as the most prevalent hearing loss following TBI, regardless of the severity of injury.11, 12, 19-22 We examined the effects of non-blast related TBI on peripheral auditory function as measured through basic and advanced audiological assessments and the overall proportion of post-traumatic hearing loss as reported across the literature. 11 We found that SNHL was the most prevalent hearing loss post-TBI at 37.3 percent in 183 of 804 overall participants across the 20 primary studies included in the review. A further finding of importance revealed substantial variability in the choice of tests administered, inconsistent cut-off criteria for determining hearing loss and reporting of hearing loss severity. Given this variability, the range and frequency of auditory deficits in this patient population remain largely unclear. However, enough evidence exists for a preliminary improved approach in the identification and diagnosis of post-traumatic hearing loss. DIAGNOSING HEARING LOSS IN PATIENTS WITH TBI An initial step in informing clinical decision making as it relates to patients with TBI is the identification of these patients in the clinical setting. Given there is a large proportion of patients with mild TBI,23 not presenting to an in-patient hospital setting, it follows that patients with mild TBI may fail to report it in tertiary settings (i.e., audiology clinics). It is therefore vital that audiologists establish the possibility of TBI during case history taking. When exploring the possibility of auditory dysfunction in the context of TBI, audiologists must consider the confounding effects of other TBI-related deficits and that a single symptom or pattern of symptoms does not characterize mild TBI. The resolution of some symptoms may take place quite promptly (i.e., minutes to hours post-injury)17 while others may persist for a longer period. Furthermore, the manifestation of symptoms may be delayed, likely untreated, and hence the consideration of such symptoms is particularly important given the heightened impact on the patient's lived experience as a result of potential functional impairment/s. Given the additional and often persistent problems associated with TBI, including emotional, cognitive, and behavioral disturbances, audiologists need to be prepared for the increased impact such symptoms will have on the diagnosis and rehabilitation of hearing loss in this patient population.16-18 CASE HISTORY TAKING In the context of TBI, the audiologist should explore the possibility of head injury by asking the question directly, supplemented with additional questions if necessary (see Fig. 1). The inquiry should start with querying a history of head injury. A negative response from the patient should not be left unexplored, the audiologist should use follow-up questions to facilitate further exploration. An additional inquiry addressing the possibility of ‘hits to the head’ during extra-curricular activities, work, or any other occasions, should follow. A negative response to the follow-up questions would be satisfactory in this instance. However, if the patient identifies and recalls an episode that involved a hit to the head, the audiologist should further investigate the episode with questions around hospitalization, loss of consciousness, possible changes in alertness, speaking, coordination, or other possible signs of injury. If the patient had suffered from a head injury, the audiologist must inquire about loss of consciousness. Also, and particularly to explore the injury severity, the audiologist should seek clarification on the nature of injury (e.g., motor vehicle accident, blow to the head, fall) and associated force (e.g., specify the object that hit the head, how s/he fell, or whether they were thrown from a vehicle). Another important aspect of further exploration would be to seek information on whether the patient was hospitalized, whether they visited the emergency department or their general practitioner (GP) and whether the head injury severity was assessed using the Glasgow Coma Scale (GCS) or some other injury severity measure. The audiologist should also seek information on whether the patient had undergone Computed Tomography (CT) and/or Magnetic Resonance Imagining (MRI) scan (Fig. 1). Considering the impact of TBI on numerous aspects of patients’ lives, the audiologist should inquire about the impact of hearing difficulties in the workplace, in social situations, and communication ability generally. Substantial consideration of comorbidities, such as anxiety and depression should guide the audiologist's approach as these comorbidities interact with communication difficulties. Factors such as cognitive fatigue, irritability, speech and language deficits, confusion, and memory difficulties will substantially affect the process of case history taking and the overall audiological appointment. Hence, the initial appointment may require the presence of a significant other. Finally, the functional, social, and emotional impacts are critical to the evaluation of effective communication ability, particularly in the context of post-traumatic auditory dysfunction.24 Therefore, the use of patient-reported outcome measures (PROMS) is strongly recommended, including the Hearing Handicap Inventory for Adults (HHIA), Tinnitus Handicap Inventory (THI), and Hyperacusis Questionnaire (HQ). This recommendation is supported by Knoll, et al.,25 who identified that a range of auditory symptoms (subjective hearing loss, tinnitus, and hyperacusis) was associated with considerable disability in patients with mild TBI (6 years post-injury) compared to controls. The findings confirm long-term bothersome auditory deficits are likely to be concealed by the complex comorbidities associated with TBI. RECOMMENDED DIAGNOSTIC TEST BATTERY In our systematic review, we noted a substantial variability in the choice of tests utilized in the assessment of auditory dysfunction following TBI.11 The most frequently utilized assessment was pure tone audiometry (PTA) in 14/20 studies, followed by Auditory Brain-stem Response (ABR) in 13/20 studies, tympanometry in 10/20 studies, speech audiometry, and acoustic reflexes in 6/20 studies, and otoacoustic emissions (OAEs) in 3/20 studies. While the evaluation of hearing loss is tailored specifically to the individual patient's presenting difficulties, the following assessments are recommended in the context of TBI (Fig. 2). First, PTA should be conducted across the frequency range between 250 Hz and 12k Hz. High-frequency hearing loss has been found in 56 percent of participants in a study by Bergemalm and Borg26 and in 26 percent of participants in a study by Munjal, Panda, and Pathak.12 Another notable study9 revealed a significant positive correlation between the severity of TBI injury and high-frequency hearing loss; as the severity of injury increased, so did the high-frequency hearing thresholds. Second, post-traumatic injury to middle ear structures should be evaluated using middle ear function measures including tympanometry and acoustic reflexes. Audiologists are, however, strongly encouraged to exclude tests not tolerated due to the potential for the patient to have reduced sound tolerance. Third, speech audiometry, particularly speech in noise testing, is a crucial aspect of the overall audiological assessment. Irrespective of the severity of TBI, one of the most commonly reported auditory problems is difficulty understanding speech in the presence of background noise, over the telephone, and spoken or long-running speech.27, 28 While there is no preferred test, audiologists are encouraged to use the adaptive signal to noise ratio tests, such as the Hearing in Noise Test (HINT)29 or the Quick Speech in Noise (Quick-SIN),30 which allow for comparison of the patient's signal to noise ratio improvement with amplification.31 Finally, the use of evoked auditory potentials, specifically the Auditory Brain Stem Response (ABR) test allows for site-of-lesion testing and estimation of hearing sensitivity in difficult to test patients. We found the ABR as the second most commonly utilized test in clinical settings, revealing abnormalities in 37.7 percent of the participants in 20 studies reviewed.11 The use of evoked potentials adds to the overall clinical picture as it contributes to the test battery particularly for those patients that are otherwise unable to undergo a subjective assessment (i.e., PTA). These assessment and case history recommendations will assist audiologists in implementing an adequate rehabilitation plan in the context of TBI and its associated difficulties. Audiologists must be open to modifying their rehabilitation plans dependent on the progression of TBI deficits and the relative impact on hearing and communication abilities of this patient population. While we did not discuss the prevalence of post-traumatic vestibular deficits, an evaluation of both auditory and vestibular deficits should be performed given the high incidence of auditory and vestibular difficulties in patients post-TBI.16-18,32-38 Audiologists who practice in exclusively auditory settings should therefore refer the patients to vestibular audiological settings, otolaryngology, and physiotherapy clinics to undergo a diagnosis and treatment of potential vestibular disturbances.

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