Relationship between severity of traumatic brain injury (TBI) and extent of auditory dysfunction

Prevalence of tinnitus following non-blast related traumatic brain injury: a systematic review of literature

OBJECTIVES

To establish the prevalence of tinnitus in adults who have sustained non-blast related traumatic brain injury (TBI), as well as the prevalence of tinnitus following TBI in the absence of hearing loss.

METHODS

A systematic search was carried out using MEDLINE, EMBASE, PsycINFO, CINAHL from January 1st 1990 to August 14th 2023. TBI, tinnitus and auditory findings were extracted from all eligible studies, and a descriptive synthesis performed. This systematic review was registered with PROSPERO (Registration number: CRD42022377637).

RESULTS

Based on the Oxford Centre of Evidence-Based Medicine (OCEBM) (2011) criteria, the highest quality evidence identified was at Level 2b, with the bulk of the included studies predominantly populating the lower evidence tiers. While there was a substantial variability in the methods used to establish and report the presence of tinnitus, its occurrence following TBI was evident in adults with and without hearing loss.

CONCLUSION

The need for prospective, longitudinal research into tinnitus following non-blast related TBI is evident. Such comprehensive studies hold the potential to inform and enhance the clinical diagnosis and management of this patient population.

Concussion acutely disrupts auditory processing in division I football student-athletes

INTRODUCTION

Diagnosis, assessment, and management of sports-related concussion require a multi-modal approach. Yet, currently, an objective assessment of auditory processing is not included. The auditory system is uniquely complex, relying on exquisite temporal precision to integrate signals across many synapses, connected by long axons. Given this complexity and precision, together with the fact that axons are highly susceptible to damage from mechanical force, we hypothesize that auditory processing is susceptible to concussive injury.

METHODS

We measured the frequency-following response (FFR), a scalp-recorded evoked potential that assesses processing of complex sound features, including pitch and phonetic identity. FFRs were obtained on male Division I Collegiate football players prior to contact practice to determine a pre-season baseline of auditory processing abilities, and again after sustaining a sports-related concussion. We predicted that concussion would decrease pitch and phonetic processing relative to the student-athlete's preseason baseline.

RESULTS

We found that pitch and phonetic encoding was smaller post-concussion. Student-athletes who sustained a second concussion showed similar declines after each injury.

CONCLUSIONS

Auditory processing should be included in the multimodal assessment of sports-related concussion. Future studies that extend this work to other sports, other injuries (e.g. blast exposure), and to female athletes are needed.

Mild Traumatic Brain Injury and the Auditory System: An Overview of the Mechanisms, Clinical Presentations, and Current Diagnostic Modalities

The acute and long-term consequences of mild traumatic brain injury (mTBI) are far reaching. Though it may often be overlooked due to the now expansive field of research dedicated to understanding the consequences of mTBI on the brain, recent work has revealed that substantial changes in the vestibulo-auditory system can also occur due to mTBI. These changes, termed "labyrinthine" or "cochlear concussion," include hearing loss, vertigo, and tinnitus that develop after mTBI in the setting of an intact bony labyrinthine capsule (as detected on imaging). In the review that follows, we focus our discussion on the effects of mTBI on the peripheral structures and pathways of the auditory and vestibular systems. Although the effects of indirect trauma (e.g., noise and blast trauma) have been well-investigated, there exists a profound need to improve our understanding of the effects of direct head injury (such as mTBI) on the auditory and vestibular systems. Our aim is to summarize the current evidentiary foundation upon which labyrinthine and/or cochlear concussion are based to shed light on the ways in which clinicians can refine the existing modalities used to diagnose and treat patients experiencing mTBI as it relates to hearing and balance.

Exploring the challenges of avoiding collisions with virtual pedestrians using a dual-task paradigm in individuals with chronic moderate to severe traumatic brain injury

BACKGROUND

Individuals with a moderate-to-severe traumatic brain injury (m/sTBI), despite experiencing good locomotor recovery six months post-injury, face challenges in adapting their locomotion to the environment. They also present with altered cognitive functions, which may impact dual-task walking abilities. Whether they present collision avoidance strategies with moving pedestrians that are altered under dual-task conditions, however, remains unclear. This study aimed to compare between individuals with m/sTBI and age-matched control individuals: (1), the locomotor and cognitive costs associated with the concurrent performance of circumventing approaching virtual pedestrians (VRPs) while attending to an auditory-based cognitive task and; (2) gaze behaviour associated with the VRP circumvention task in single and dual-task conditions.

METHODOLOGY

Twelve individuals with m/sTBI (age = 43.3 ± 9.5 yrs; >6 mo. post injury) and 12 healthy controls (CTLs) (age = 41.8 ± 8.3 yrs) were assessed while walking in a virtual subway station viewed in a head-mounted display. They performed a collision avoidance task with VRPs, as well as auditory-based cognitive tasks (pitch discrimination and auditory Stroop), both under single and dual-task conditions. Dual-task cost (DTC) for onset distance of trajectory deviation, minimum distance from the VRP, maximum lateral deviation, walking speed, gaze fixations and cognitive task accuracy were contrasted between groups using generalized estimating equations.

RESULTS

In contrast to CTLs who showed locomotor DTCs only, individuals with m/sTBI displayed both locomotor and cognitive DTCs. While both groups walked slower under dual-task conditions, only individuals with m/sTBI failed to modify their onset distance of trajectory deviation and maintained smaller minimum distances and smaller maximum lateral deviation compared to single-task walking. Both groups showed shorter gaze fixations on the approaching VRP under dual-task conditions, but this reduction was less pronounced in the individuals with m/sTBI. A reduction in cognitive task accuracy under dual-task conditions was found in the m/sTBI group only.

CONCLUSION

Individuals with m/sTBI present altered locomotor and gaze behaviours, as well as altered cognitive performances, when executing a collision avoidance task involving moving pedestrians in dual-task conditions. Potential mechanisms explaining those alterations are discussed. Present findings highlight the compromised complex walking abilities in individuals with m/sTBI who otherwise present a good locomotor recovery.

Comprehensive behavioral and physiologic assessment of peripheral and central auditory function in individuals with mild traumatic brain injury

Auditory complaints are frequently reported by individuals with mild traumatic brain injury (mTBI) yet remain difficult to detect in the absence of clinically significant hearing loss. This highlights a growing need to identify sensitive indices of auditory-related mTBI pathophysiology beyond pure-tone thresholds for improved hearing healthcare diagnosis and treatment. Given the heterogeneity of mTBI etiology and the diverse peripheral and central processes required for normal auditory function, the present study sought to determine the audiologic assessments sensitive to mTBI pathophysiology at the group level using a well-rounded test battery of both peripheral and central auditory system function. This test battery included pure-tone detection thresholds, word understanding in quiet, sentence understanding in noise, distortion product otoacoustic emissions (DPOAEs), middle-ear muscle reflexes (MEMRs), and auditory evoked potentials (AEPs), including auditory brainstem responses (ABRs), middle latency responses (MLRs), and late latency responses (LLRs). Each participant also received magnetic resonance imaging (MRI). Compared to the control group, we found that individuals with mTBI had reduced DPOAE amplitudes that revealed a compound effect of age, elevated MEMR thresholds for an ipsilateral broadband noise elicitor, longer ABR Wave I latencies for click and 4 kHz tone burst elicitors, longer ABR Wave III latencies for 4 kHz tone bursts, larger MLR Na and Nb amplitudes, smaller MLR Pb amplitudes, longer MLR Pa latencies, and smaller LLR N1 amplitudes for older individuals with mTBI. Further, mTBI individuals with combined hearing difficulty and noise sensitivity had a greater number of deficits on thalamic and cortical AEP measures compared to those with only one/no self-reported auditory symptoms. This finding was corroborated with MRI, which revealed significant structural differences in the auditory cortical areas of mTBI participants who reported combined hearing difficulty and noise sensitivity, including an enlargement of left transverse temporal gyrus (TTG) and bilateral planum polare (PP). These findings highlight the need for continued investigations toward identifying individualized audiologic assessments and treatments that are sensitive to mTBI pathophysiology.

A cross-sectional survey of non-specialist Australian audio-vestibular clinical practice for traumatic brain injury and rehabilitation

OBJECTIVE

This study explored non-specialist audiological clinical practice in the context of traumatic brain injury (TBI), and whether such practices incorporated considerations of TBI-related complexities pertaining to identification, diagnosis and management of associated auditory and vestibular disturbances.

DESIGN

A cross-sectional online survey exploring clinical practice, TBI-related training and information provision was distributed to audiologists across Australia via Audiology Australia and social media. Fifty audiologists, 80% female and 20% male, participated in this study. Years of professional practice ranged from new graduate to more than 20 years of experience.

RESULTS

Clear gaps of accuracy in knowledge and practice across all survey domains relating to the identification, diagnosis and management of patients with auditory and/or vestibular deficits following TBI were evident. Further, of the surveyed audiologists working in auditory and vestibular settings, 91% and 86%, respectively, reported not receiving professional development for the diagnosis and management of post-traumatic audio-vestibular deficits.

CONCLUSION

Inadequate resources, equipment availability and TBI-related training may have contributed to the gaps in service provision, influencing audiological management of patients with TBI. A tailored TBI approach to identification, diagnosis and management of post-traumatic auditory and vestibular disturbances is needed.

A Scoping Review of Auditory Dysfunction After Childhood Traumatic Brain Injury

PURPOSE

The purpose of this scoping review was to gain an understanding of the evidence available on auditory dysfunction after childhood traumatic brain injury (TBI) and identify limitations, clinical implications, and future directions for speech-language pathology and audiology practice and research.

METHOD

This scoping review of the literature followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews guidelines.

RESULTS

A total of eight articles met inclusion for this scoping review. All studies were observational studies (n = 4 with controls, n = 4 without controls). Age at injury, injury severity, time postinjury, and age at time of study varied across the included studies. Three major topics related to childhood TBI were addressed among the included studies: (a) prevalence of auditory dysfunction (n = 5), (b) functional outcomes and biological markers related to auditory processing (n = 2), and (c) clinical presentation of auditory dysfunction (n = 2).

CONCLUSIONS

This review highlights the particular lack of experimental evidence related to risk and protective factors and assessment and management strategies related to auditory dysfunction after childhood TBI. There is a major need for more research and research of higher rigor to be conducted with individuals who experienced a childhood TBI to support audiologists' and speech-language pathologists' evidence-based decision making to improve long-term functional outcomes for children with TBI.

'I had nothing. It's just life experience that helped me through that situation': Australian audiologists' perspectives on audiological clinical practice for traumatic brain injury and rehabilitation

OBJECTIVE

Australian Audiologists' perspectives on standard non-specialized clinical practice in the context of Traumatic Brain Injury (TBI) were examined, including the perceived barriers to optimal service provision.

DESIGN

A qualitative research design utilizing semi-structured interviews was conducted using purposive sampling. Nine participants were interviewed about their understanding of the impact of TBI on hearing and balance; identification, diagnosis and management of auditory and vestibular dysfunction following TBI; barriers to service delivery; training relating to complex clients (i.e., TBI); and awareness of referral pathways.

RESULTS

Three major themes, each with subthemes, were evident in the data. The major themes reflected general considerations of audiological professional culture and specific issues related to knowledge of TBI and clinical practice with patients. Analysis revealed that professional culture seemed to act as a contextual barrier and interacted with the perceived lack of TBI related knowledge to hinder optimal clinical practice in this patient population.

CONCLUSION

Application of the biopsychosocial model, including interdisciplinary care in the management of patients with TBI, is needed. An improvement in theoretical and practical knowledge encompassing the wide-ranging effects of TBI is critical for the optimal audiological service delivery.

A Retrospective Study of the Effects of Traumatic Brain Injury on Auditory Function: From a Clinical Perspective

Purpose: The main purpose of this retrospective study was to identify auditory dysfunctions related to traumatic brain injury (TBI) in individuals evaluated in an Audiology clinic. Method: Peripheral and central auditory evaluations were performed from March 2014 to June 2018 in 26 patients (14 males) with TBI. The age of the participants ranged from 9 to 59 years old (34.24 ± 15.21). Six participants had blast-related TBI and 20 had blunt force TBI. Sixteen experienced a single TBI event whereas ten experienced several. Correlation analyses were performed to verify the relationship, if any, between the number of auditory tests failed and the number, type, and severity of TBIs. Result: All participants failed at least one auditory test. Nearly 60% had abnormal results on degraded speech tests (compressed and echoed, filtered or in background noise) and 25% had a high frequency hearing loss. There was no statistically significant correlation between the number of auditory tests failed and the number, type, and severity of TBIs. Conclusion: Results indicated negative and heterogenous effects of TBI on peripheral and central auditory function and highlighted the need for a more extensive auditory assessment in individuals with TBI.

Toward a global and reproducible science for brain imaging in neurotrauma: the ENIGMA adult moderate/severe traumatic brain injury working group

The global burden of mortality and morbidity caused by traumatic brain injury (TBI) is significant, and the heterogeneity of TBI patients and the relatively small sample sizes of most current neuroimaging studies is a major challenge for scientific advances and clinical translation. The ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis) Adult moderate/severe TBI (AMS-TBI) working group aims to be a driving force for new discoveries in AMS-TBI by providing researchers world-wide with an effective framework and platform for large-scale cross-border collaboration and data sharing. Based on the principles of transparency, rigor, reproducibility and collaboration, we will facilitate the development and dissemination of multiscale and big data analysis pipelines for harmonized analyses in AMS-TBI using structural and functional neuroimaging in combination with non-imaging biomarkers, genetics, as well as clinical and behavioral measures. Ultimately, we will offer investigators an unprecedented opportunity to test important hypotheses about recovery and morbidity in AMS-TBI by taking advantage of our robust methods for large-scale neuroimaging data analysis. In this consensus statement we outline the working group's short-term, intermediate, and long-term goals.

Towards detection of brain injury using multimodal non-invasive neuromonitoring in adults undergoing extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a form of cardiopulmonary bypass that provides life-saving support to critically ill patients whose illness is progressing despite maximal conventional support. Use in adults is expanding, however neurological injuries are common. Currently, the existing brain imaging tools are a snapshot in time and require high-risk patient transport. Here we assess the feasibility of measuring diffuse correlation spectroscopy, transcranial Doppler ultrasound, electroencephalography, and auditory brainstem responses at the bedside, and developing a cerebral autoregulation metric. We report preliminary results from two patients, demonstrating feasibility and laying the foundation for future studies monitoring neurological health during ECMO.

Auditory Quality-of-Life Measures in Patients With Traumatic Brain Injury and Normal Pure Tone Audiometry

Auditory complaints are commonly reported following traumatic brain injury (TBI). However, few studies have examined patient-reported auditory symptomatology and quality-of-life metrics in individuals with TBI. We hypothesize that following TBI, individuals can experience auditory symptoms even with hearing thresholds in the normal range. Adult patients with normal auditory thresholds and a history of TBI were evaluated for subjective hearing loss, tinnitus, aural fullness, hyperacusis, and autophony. Hearing Handicap Inventory for Adults, Tinnitus Handicap Inventory, and Hyperacusis Questionnaire were administered. Thirty-one patients were prospectively recruited. Twenty-eight TBI participants (90%) reported ≥1 auditory symptoms at the time of survey intake. Mild to severe handicap in the Hearing Handicap Inventory for Adults and Tinnitus Handicap Inventory was reported in 71.4% and 40% of the participants with hearing loss and tinnitus, respectively. Hyperacusis handicap was considered significant in 41.1% of the participants who complained of hyperacusis and completed the survey. Despite normal hearing thresholds, individuals with TBI experience decrements in auditory quality-of-life metrics. Level of evidence: 3.

Long-term cochlear implantation outcomes in patients following head injury

OBJECTIVE

In cases of a severe to profound sensorineural hearing loss following head injury, the cochlear implant (CI) is the primary option for auditory rehabilitation. Few studies, however, have investigated long-term CI outcomes in patients following head trauma, including those without temporal bone fracture (TBF). Herein, the aim of this study is to examine CI outcomes following cases of head injury with and without TBF.

METHODS

Audiometric outcomes of patients who received a CI due to a head injury resulting in severe to profound hearing loss at two tertiary care hospitals were analyzed. Patients were divided into those who received a CI in a fractured temporal bone (group A, n = 11 patients corresponding to 15 ears) and those who received a CI in a non-fractured temporal bone (group B, n = 8 patients corresponding to nine ears). Primary outcomes included duration of deafness prior to CI and postoperative consonant-nucleus-constant whole word (CNC) scores.

RESULTS

Nineteen patients (84% male), corresponding to 24 CIs, were identified. Fifteen CI were performed on ears with TBF (group A), and nine CI were performed on ears without TBF (group B). No patients had an enlarged vestibular aqueduct (EVA). The mean duration of deafness was 5.7 and 11.3 years in group A and group B, respectively. The mean duration of CI follow-up (CI experience) was 6.5 years in group A and 2.1 years in group B. The overall mean postoperative CNC score for all subjects was 68.6% (±21.2%, n = 19 with CNC testing). There was no difference in CNC score between group A and group B (69.8% and 66% respectively, P = .639).

CONCLUSION

The study is among the largest series examining long-term outcomes of CI after head injury. CI is an effective method for auditory rehabilitation in patients after head injury.

LEVEL OF EVIDENCE

IV.

A Review of the Role of Auditory Evoked Potentials in Mild Traumatic Brain Injury Assessment

Around 75% to 90% of people who experience a traumatic brain injury (TBI) are classified as having a mild TBI (mTBI). The term mTBI is synonymous with concussion or mild head injury (MHI) and is characterized by symptoms of headache, nausea, dizziness, and blurred vision. Problems in cognitive abilities such as deficits in memory, processing speed, executive functioning, and attention are also considered symptoms of mTBI. Since these symptoms are subtle in nature and may not appear immediately following the injury, mTBI is often undetected on conventional neuropsychological tests. Current neuroimaging techniques may not be sensitive enough in identifying the array of microscopic neuroanatomical and subtle neurophysiological changes following mTBI. To this end, electrophysiological tests, such as auditory evoked potentials (AEPs), can be used as sensitive tools in tracking physiological changes underlying physical and cognitive symptoms associated with mTBI. The purpose of this review article is to examine the body of literature describing the application of AEPs in the assessment of mTBI and to explore various parameters of AEPs which may hold diagnostic value in predicting positive rehabilitative outcomes for people with mTBI.

Reversible conductive hearing impediments among patients with severe brain injury

Purpose: Rehabilitation of patients with severe traumatic brain injury may include auditory stimuli. Hampering the function of the external, middle ear or Eustachian tube generates a conductive auditory deficit up to 35 dB that may potentially hinder auditory rehabilitation. The objective was to evaluate the incidence of conductive hearing impediments among patients with severe brain injury.Methods: The cross-section study included adults with severe brain injury hospitalized in a rehabilitation center. The patients presented with a prolonged vegetative state, were dependent on mechanical ventilation and gastrostomy tube feeding. Assessment of external, middle ear and Eustachian tube included otoscopy, tympanometry, nasopharyngoscopy, gag reflex and soft palate evaluations.Results: Nineteen patients (38 ears) were evaluated: 14 males and 5 females, aged 18-93 years (average 59). All patients had a normal nasopharynx, lacked a gag reflex, palatal movements or supraglottic sensation. Eighteen ears (47%) had middle ear effusion, 26 (68%) ears had cerumen impaction, and 14 (37%) had both.Conclusions: Many patients with severe brain injury have reversible and treatable impairments that cause potential conductive hearing loss. Routine otoscopic examination and treatment if required, that is, removal of impacted cerumen or middle ear drainage, have rehabilitating and general health benefits.Implications for rehabilitationAuditory stimulation was suggested for rehabilitation in patients with severe traumatic brain injury.Many patients have cerumen and/or otitis media with effusion causing conductive hearing impairment as well as general health issues.Both aural impediments are diagnosed by routine otoscopy, are easily treated, and may affect rehabilitation.

Hearing complaints among veterans following traumatic brain injury

It has been shown that there is an increased risk for impaired auditory function following traumatic brain injury (TBI) in Veterans. Evidence is strongest in the area of self-report, but behavioural and electro-physiological data have been obtained that are consistent with these complaints. Peripheral and central dysfunction have both been observed. Historically, studies have focused on penetrating head injuries where central injury is more easily documented than in mild closed head injuries, but several recent reports have expanded the literature to include closed head injuries as well. The lack of imaging technology that can identify which closed head injuries are likely to impact auditory function is a significant barrier to accurate diagnosis and rehabilitation. Current behavioural and electrophysiological measures are effective in substantiating the auditory complaints of these patients but leave many questions unanswered. One significant limitation of current approaches is the lack of clear data regarding the potential influence of those mental health comorbidities that are very likely to be present in the Veteran population. In the area of rehabilitation, there are indications that hearing aids and other assistive listening devices may provide benefit, as can auditory training programmes, yet more research needs to be done.

Time course of blast-induced injury in the rat auditory cortex

Blast exposure is an increasingly significant health hazard and can have a range of debilitating effects, including auditory dysfunction and traumatic brain injury. To assist in the development of effective treatments, a greater understanding of the mechanisms of blast-induced auditory damage and dysfunction, especially in the central nervous system, is critical. To elucidate this area, we subjected rats to a unilateral blast exposure at 22 psi, measured their auditory brainstem responses (ABRs), and histologically processed their brains at 1 day, 1 month, and 3-month survival time points. The left and right auditory cortices was assessed for astrocytic reactivity and axonal degenerative changes using glial fibrillary acidic protein immunoreactivity and a silver impregnation technique, respectively. Although only unilateral hearing loss was induced, astrocytosis was bilaterally elevated at 1 month post-blast exposure compared to shams, and showed a positive trend of elevation at 3 months post-blast. Axonal degeneration, on the other hand, appeared to be more robust at 1 day and 3 months post-blast. Interestingly, while ABR threshold shifts recovered by the 1 and 3-month time-points, a positive correlation was observed between rats’ astrocyte counts at 1 month post-blast and their threshold shifts at 1 day post-blast. Taken together, our findings suggest that central auditory damage may have occurred due to biomechanical forces from the blast shockwave, and that different indicators/types of damage may manifest over different timelines.

Prevalence and correlates of traumatic brain injury (TBI) in older adults: results from the Well-being of the Singapore Elderly (WiSE) study

BACKGROUND

Older adults are among the most susceptible to sustain traumatic brain injury (TBI). The study aimed to determine the (1) prevalence of TBI among older adults in Singapore, and (2) socio-demographic, lifestyle, and clinical correlates of TBI.

METHODS

Data were extracted from the cross-sectional, Well-being of the Singapore Elderly (WiSE) study. The study included 2,565 participants aged 60 years and above (Mean = 72.75, SD = 9.54). Information on TBI, socio-demographic, and lifestyle factors were collected using participant self-report and verified with the informant report where necessary. Disability was measured using the World Health Organization - Disability Assessment Schedule 2.0 (WHO-DAS 2.0). Data were analyzed using logistic regression analysis.

RESULTS

The prevalence of TBI was 3.6%. Being female (vs. male) was found to be associated with decreased odds of having TBI. Having completed secondary education or lower (vs. tertiary education) was found to be associated with increased odds of having TBI. A history of fainting and diabetes were associated with the presence of TBI. Those with TBI were associated with higher disability scores on the WHO-DAS 2.0 than those without TBI.

CONCLUSIONS

The current study provides information on the prevalence and associated factors of TBI in the older adult population in Singapore. Since TBI was associated with older adults with diabetes, they must be cautioned about fall risk. Also, given the association with disability, older adults with TBI are likely to require support and rehabilitative care to ensure good quality of life.

Impact of mild traumatic brain injury on auditory brain stem dysfunction in mouse model

The auditory brainstem response (ABR) is an electrophysiological test that examines the functionality of the auditory nerve and brainstem. Traumatic brain injury (TBI) can be detected if prolonged peak latency is observed in ABR measurements, since latency measures the neural conduction time in the brainstem, and an increase in latency can be a sign of pathological lesion at the auditory brainstem level. The ABR is elicited by brief sounds that can be used to measure hearing sensitivity as well as temporal processing. Reduction in peak amplitudes and increases in latency are indicative of dysfunction in the auditory nerve and/or central auditory pathways. In this study we used sixteen young adult mice that were divided into two groups: sham and mild traumatic brain injury (mTBI), with ABR measurements obtained prior to, and at 2, 6, and 14 weeks after injury. Abnormal ABRs were observed for the nine TBI cases as early as two weeks after injury and the deficits lasted for fourteen weeks after injury. Results indicated a significant reduction in the Peak 1 (P1) and Peak 4 (P4) amplitudes to the first noise burst, as well as an increase in latency response for P1 and P4 following mTBI. These results are the first to demonstrate auditory sound processing deficits in a rodent model of mild TBI.

Sensory coding and cognitive processing of sound in Veterans with blast exposure

Recent anecdotal reports from VA audiology clinics as well as a few published studies have identified a sub-population of Service Members seeking treatment for problems communicating in everyday, noisy listening environments despite having normal to near-normal hearing thresholds. Because of their increased risk of exposure to dangerous levels of prolonged noise and transient explosive blast events, communication problems in these soldiers could be due to either hearing loss (traditional or "hidden") in the auditory sensory periphery or from blast-induced injury to cortical networks associated with attention. We found that out of the 14 blast-exposed Service Members recruited for this study, 12 had hearing thresholds in the normal to near-normal range. A majority of these participants reported having problems specifically related to failures with selective attention. Envelope following responses (EFRs) measuring neural coding fidelity of the auditory brainstem to suprathreshold sounds were similar between blast-exposed and non-blast controls. Blast-exposed subjects performed substantially worse than non-blast controls in an auditory selective attention task in which listeners classified the melodic contour (rising, falling, or "zig-zagging") of one of three simultaneous, competing tone sequences. Salient pitch and spatial differences made for easy segregation of the three concurrent melodies. Poor performance in the blast-exposed subjects was associated with weaker evoked response potentials (ERPs) in frontal EEG channels, as well as a failure of attention to enhance the neural responses evoked by a sequence when it was the target compared to when it was a distractor. These results suggest that communication problems in these listeners cannot be explained by compromised sensory representations in the auditory periphery, but rather point to lingering blast-induced damage to cortical networks implicated in the control of attention. Because all study participants also suffered from post-traumatic disorder (PTSD), follow-up studies are required to tease apart the contributions of PTSD and blast-induced injury on cognitive performance.

The Application of the International Classification of Functioning, Disability and Health to Functional Auditory Consequences of Mild Traumatic Brain Injury

This article reviews the auditory consequences of mild traumatic brain injury (mTBI) within the context of the International Classification of Functioning, Disability and Health (ICF). Because of growing awareness of mTBI as a public health concern and the diverse and heterogeneous nature of the individual consequences, it is important to provide audiologists and other health care providers with a better understanding of potential implications in the assessment of levels of function and disability for individual interdisciplinary remediation planning. In consideration of body structures and function, the mechanisms of injury that may result in peripheral or central auditory dysfunction in mTBI are reviewed, along with a broader scope of effects of injury to the brain. The activity limitations and participation restrictions that may affect assessment and management in the context of an individual's personal factors and their environment are considered. Finally, a review of management strategies for mTBI from an audiological perspective as part of a multidisciplinary team is included.

Electrophysiologic recordings in traumatic brain injury

Following a traumatic brain injury (TBI), the brain undergoes numerous electrophysiologic changes. The most common techniques used to evaluate these changes include electroencepalography (EEG) and evoked potentials. In animals, EEGs immediately following TBI can show either diffuse slowing or voltage attenuation, or high voltage spiking. Following a TBI, many animals display evidence of hippocampal excitability and a reduced seizure threshold. Some mice subjected to severe TBI via a fluid percussion injury will eventually develop seizures, which provides a useful potential model for studying the neurophysiology of epileptogenesis. In humans, the EEG changes associated with mild TBI are relatively subtle and may be challenging to distinguish from EEG changes seen in other conditions. Quantitative EEG (QEEG) may enhance the ability to detect post-traumatic electrophysiologic changes following a mild TBI. Some types of evoked potential (EP) and event related potential (ERP) can also be used to detect post-traumatic changes following a mild TBI. Continuous EEG monitoring (cEEG) following moderate and severe TBI is useful in detecting the presence of seizures and status epilepticus acutely following an injury, although some seizures may only be detectable using intracranial monitoring. CEEG can also be helpful for assessing prognosis after moderate or severe TBI. EPs, particularly somatosensory evoked potentials, can also be useful in assessing prognosis following severe TBI. The role for newer technologies such as magnetoencephalography and bispectral analysis (BIS) in the evaluation of patients with TBI remains unclear.

Negative neuroplasticity in chronic traumatic brain injury and implications for neurorehabilitation

Based on growing findings of brain volume loss and deleterious white matter alterations during the chronic stages of injury, researchers posit that moderate-severe traumatic brain injury (TBI) may act to “age” the brain by reducing reserve capacity and inducing neurodegeneration. Evidence that these changes correlate with poorer cognitive and functional outcomes corroborates this progressive characterization of chronic TBI. Borrowing from a framework developed to explain cognitive aging (Mahncke et al., Progress in Brain Research, 157, 81–109, 2006a; Mahncke et al., Proceedings of the National Academy of Sciences of the United States of America, 103(33), 12523–12528, 2006b), we suggest here that environmental factors (specifically environmental impoverishment and cognitive disuse) contribute to a downward spiral of negative neuroplastic change that may modulate the brain changes described above. In this context, we review new literature supporting the original aging framework, and its extrapolation to chronic TBI. We conclude that negative neuroplasticity may be one of the mechanisms underlying cognitive and neural decline in chronic TBI, but that there are a number of points of intervention that would permit mitigation of this decline and better long-term clinical outcomes.

Assessment of the risk factors for hearing loss in adult Nigerian population

BACKGROUND

A reduction in hearing sensitivity is common in adults and was previously considered to be normal as age increases. However, other health variables may play a role in the sensory changes. This prospective, comparative, hospital-based study assessed the risk factors (RFs) associated with sensorineural hearing losses (SNHL) in adult patients in a specialized tertiary hospital clinic in South-western Nigeria.

MATERIALS AND METHODS

Patients with clinical diagnosis of hearing impairment (bilateral SNHL) were the test subjects and age and sex-matched comparable group without SNHL were the Controls. Using a structured questionnaire, variables assessed included current and past medical history, family and social history, use of medications including ototoxic drugs, and prolonged medications.

RESULTS

One hundred and twenty-seven patients participated in the study comprising of 76 test subjects with SNHL (including 14 with suspected ARHL) and 51 controls. 59.8% of the participants were males. Univariate analysis revealed statistically-significant differences in family history, alcohol consumption, smoking, exposure to noise, previous ear discharge, previous head injury, hypertension, diabetes, osteoarthritis, ototoxic drugs usage, prolonged medication and obesity between the two categories of subjects. Logistic regression analysis revealed family history, smoking, noise exposure, head injury, hypertension had significantly increased odds of developing SNHL.

CONCLUSION

It was concluded that the RFs for SNHL in adult Nigerians were multifactorial while some of the RFs may be amenable to primary prevention. Legislation and public health education could facilitate reduction of SNHL in our community.

Otologic assessment of blast and nonblast injury in returning Middle East-deployed service members

OBJECTIVES/HYPOTHESIS

To determine if tympanic membrane perforation offers any protection from inner ear damage and determine the incidence and pattern of otologic blast injury in military personnel returning from deployment.

STUDY DESIGN

Retrospective analysis of US service members injured in Operation Iraqi Freedom and Operation Enduring Freedom from October 2006 to October 2007.

METHODS

One-hundred ten blast-injured patients were compared to 54 nonblast-injured patients returning from deployment. Data captured included audiogram results, presence of tympanic membrane perforation, demographic data, location and nature of injury, loss of consciousness, sleep disturbance, confusion, and symptoms of headache, dizziness, memory loss, and tinnitus.

RESULTS

Of 110 blast-injured patients, 18 patients suffered tympanic membrane perforation (16%), of which nine patients suffered bilateral tympanic membrane perforation (8%). Blast patients suffered more hearing loss than controls as measured by pure-tone averages of varying speech reception frequencies and at 6,000 Hz. Of the blast patients who recorded an audiogram, nearly 24% suffered moderate to profound hearing loss. There was no statistically significant difference in hearing outcomes between blast-injured patients with tympanic membrane perforations and those without; however, when comparing patients with unilateral perforations with their contralateral ear, there was a difference in hearing thresholds at 6,000 Hz. There was a significantly increased risk of tinnitus, memory loss, headache, and dizziness between blast-injured patients compared to controls.

CONCLUSIONS

Due to its violent nature, blast exposure causes greater neuro-otological manifestations and deserves prompt otologic evaluation.

Electrophysiological assessments of cognition and sensory processing in TBI: applications for diagnosis, prognosis and rehabilitation

Traumatic brain injuries are often associated with damage to sensory and cognitive processing pathways. Because evoked potentials (EPs) and event-related potentials (ERPs) are generated by neuronal activity, they are useful for assessing the integrity of neural processing capabilities in patients with traumatic brain injury (TBI). This review of somatosensory, auditory and visual ERPs in assessments of TBI patients is provided with the hope that it will be of interest to clinicians and researchers who conduct or interpret electrophysiological evaluations of this population. Because this article reviews ERP studies conducted in three different sensory modalities, involving patients with a wide range of TBI severity ratings and circumstances, it is difficult to provide a coherent summary of findings. However, some general trends emerge that give rise to the following observations and recommendations: 1) bilateral absence of somatosensory evoked potentials (SEPs) is often associated with poor clinical prognosis and outcome; 2) the presence of normal ERPs does not guarantee favorable outcome; 3) ERPs evoked by a variety of sensory stimuli should be used to evaluate TBI patients, especially those with severe injuries; 4) time since onset of injury should be taken into account when conducting ERP evaluations of TBI patients or interpreting results; 5) because sensory deficits (e.g., vision impairment or hearing loss) affect ERP results, tests of peripheral sensory integrity should be conducted in conjunction with ERP recordings; and 6) patients' state of consciousness, physical and cognitive abilities to respond and follow directions should be considered when conducting or interpreting ERP evaluations.