Common causes of hearing loss in humans - exposure to loud noise or ototoxic drugs and aging - often damage sensory hair cells, reflected as elevated thresholds on the clinical audiogram. Recent ...studies in animal models suggest, however, that well before this overt hearing loss can be seen, a more insidious, but likely more common, process is taking place that permanently interrupts synaptic communication between sensory inner hair cells and subsets of cochlear nerve fibers. The silencing of affected neurons alters auditory information processing, whether accompanied by threshold elevations or not, and is a likely contributor to a variety of perceptual abnormalities, including speech-in-noise difficulties, tinnitus and hyperacusis. Work described here will review structural and functional manifestations of this cochlear synaptopathy and will consider possible mechanisms underlying its appearance and progression in ears with and without traditional ‘hearing loss’ arising from several common causes in humans.
•Noise can cause rapid synaptic loss and slow degeneration of cochlear nerve fibers, even if hair cells survive.•Diffuse cochlear synaptopathy does not raise audiometric or ABR thresholds, but does decrease ABR amplitudes.•Ears exposed to ‘synaptopathic’ noise show exaggerated synaptic and neural losses as they age after exposure.
Progressive Hearing Loss in Early Childhood Barreira-Nielsen, Carmen; Fitzpatrick, Elizabeth; Hashem, Serena ...
Ear and hearing,
2016 Sep-Oct, Volume:
37, Issue:
5
Journal Article
Peer reviewed
Deterioration in hearing thresholds in children is of concern due to the effect on language development. Before universal newborn hearing screening (UNHS), accurate information on the progression of ...hearing loss was difficult to obtain due to limited information on hearing loss onset. The objective of this population-based study was to document the proportion of children who experienced progressive loss in a cohort followed through a UNHS program in one region of Canada. We explored risk factors for progression including risk indicators, audiologic, and clinical characteristics of children. We also investigated deterioration in hearing as a function of age. For this study, two working definitions of progressive hearing loss were adopted: (1) a change of ≥20 dB in the 3 frequencies (500, 1000, and 2000 Hz) pure-tone average, and (2) a decrease of ≥10 dB at two or more adjacent frequencies between 500 and 4000 Hz or a decrease in 15 dB at one octave frequency in the same frequency range.
Population-based data were collected prospectively on a cohort of children identified from 2003 to 2013 after the implementation of UNHS. Clinical characteristics including risk indicators (as per Joint Committee on Infant Hearing), age at diagnosis, type and severity of hearing loss, and initial audiologic information were recorded when children were first identified with hearing loss. Serial audiometric results were extracted from the medical charts for this study. Differences between children with progressive and stable hearing loss were explored using χ tests. Association between risk indicators and progressive hearing loss was assessed through logistic regression. The cumulative amount of deterioration in hearing from 1 to 4 years of age was also examined.
Our analysis of 330 children (251 exposed to screening) with detailed audiologic records showed that 158 (47.9%) children had some deterioration (at least ≥10 dB and) in hearing thresholds in at least one ear. The 158 children included 76 (48.1%) with ≥20 dB loss in pure-tone average in at least one ear and 82 (51.9%) with less deterioration in hearing levels (≥10 but <20 dB). In the children with progressive hearing loss, of 131 children initially diagnosed with bilateral loss, 75 (57.3%) experienced deterioration in 1 ear and 56 (112 ears; 42.7%) in both ears (total of 187 ears). Of 27 children with an initial diagnosis of unilateral loss, 25 experienced deterioration in the impaired ear and 5 in the normal-hearing ear, progressing to bilateral hearing loss. Within 4 years after diagnosis, the mean decrease in hearing for children with progressive loss was 25.9 dB (SD: 16.4) in the right ear and 28.3 dB (SD: 12.9) in the left ear. We explored the risk factors for hearing loss identified by Joint Committee on Infant Hearing where there were sufficient numbers in our sample. On multivariate analysis, there was no statistically significant relationship between most risk indicators examined (neonatal intensive care unit admission, family history, syndromes, and postnatal infections) and the likelihood of progressive loss. However, the presence of craniofacial anomalies was inversely associated with risk of progressive hearing loss (odds ratio = 0.27; 95% confidence interval: 0.10, 0.71; p = 0.01), that is, these children were more likely to have stable hearing.
Given that almost half of the children in this cohort experienced deterioration in hearing, close postneonatal monitoring of hearing following early hearing loss identification is essential to ensure optimal amplification and therapy.
The previous 30 years have provided information on the mechanisms of cell death in the inner ear after noise exposure, ototoxic drug injury, and during aging, and clinical trials have emerged for all ...of these acquired forms of hearing loss. Sudden hearing loss is less well understood, but restoration of hearing after sudden hearing loss is also a long-standing drug target, typically using steroids as an intervention but with other agents of interest as well.
The purpose of this review was to describe the state of the science regarding clinical testing of investigational medicinal products for the inner ear with respect to treatment or prevention of acquired hearing loss.
Comprehensive search and summary of clinical trials listed in the National Library of Medicine (www.
gov) database identified 61 clinical trials.
Study phase, status, intervention, and primary, secondary, and other outcomes are summarized for studies assessing prevention of noise-induced hearing loss, prevention of drug-induced hearing loss, treatment of stable sensorineural hearing loss, and treatment of sudden sensorineural hearing loss.
This review provides a comprehensive summary of the state of the science with respect to investigational medicinal products for the inner ear evaluated in human clinical trials, and the current challenges for the field.
Background: Bilateral sudden sensorineural hearing loss (BSSHL) is rare and assumed to be a different clinical entity compared to unilateral SSHL (USSHL). This study examined the differences between ...the idiopathic BSSHL and USSHL.
Methods: Forty-six sequential BSSHL patients (Se-BSSHL) and 68 simultaneous BSSHL (Si-BSSHL) were consecutively admitted between June 2008 and December 2015. Two sets of patients served as control groups: (1) USSHL patients with healthy contralateral ear and (2) USSHL patients with contralateral preexisting hearing loss (USSHLwCHL). We retrospectively analyzed differences among four cohorts using analysis of variance, Kruskal-Wallis test, Welch's t-test, and Chi-square test as appropriate before and after propensity score matching (PSM) based on age, gender, and body mass index (BMI).
Results: The prevalence of idiopathic BSSHL was 8.6% (114/1329) among the total SSHL patients. In the total cohort, USSHL patients tended to be younger, female, and tended to have lower BMI, renal parameters, and total cholesterol in addition to higher high-density lipoprotein compared to the other three groups. Most routine blood indicators, some coagulation markers, and immunoglobulin M (H = 13.4, P = 0.004) were significantly different among the study groups. After PSM, the major significant differences were found in audiometric characteristics. Si-BSSHL and Se-BSSHL patients demonstrated similar hearing thresholds as USSHL but were significantly better than the USSHLwCHL patients across most frequencies before and after treatment (H = 30.0, P < 0.001 for initial hearing and H = 12.0, P = 0.007 for final hearing). Moreover, the BSSHL patients showed different hearing loss distribution patterns (more descending type, χ2 = 33.8, P = 0.001) with less hearing gain (H = 17.5, P < 0.001) compared to the USSHL patients.
Conclusions: Idiopathic BSSHL is a relatively rare subtype of SSHL with a higher rate of descending audiogram type and inferior hearing outcome rather than being classified as a completely different disease entity compared to USSHL.
•Mitochondrial dysfunction and oxidative stress play a central etiological role in the development of sensorineural hearing loss, either inherited or acquired.•Cochlear cells are susceptible to ...oxidative damage due to their high metabolic demands.•Many promising antioxidant therapies for the prevention and treatment of acquired sensorineural hearing loss are in preclinical and clinical development.
Sensorineural hearing loss (SNHL) can either be genetically inherited or acquired as a result of aging, noise exposure, or ototoxic drugs. Although the precise pathophysiological mechanisms underlying SNHL remain unclear, an overwhelming body of evidence implicates mitochondrial dysfunction and oxidative stress playing a central etiological role. With its high metabolic demands, the cochlea, particularly the sensory hair cells, stria vascularis, and spiral ganglion neurons, is vulnerable to the damaging effects of mitochondrial reactive oxygen species (ROS). Mitochondrial dysfunction and consequent oxidative stress in cochlear cells can be caused by inherited mitochondrial DNA (mtDNA) mutations (hereditary hearing loss and aminoglycoside-induced ototoxicity), accumulation of acquired mtDNA mutations with age (age-related hearing loss), mitochondrial overdrive and calcium dysregulation (noise-induced hearing loss and cisplatin-induced ototoxicity), or accumulation of ototoxic drugs within hair cell mitochondria (drug-induced hearing loss). In this review, we provide an overview of our current knowledge on the role of mitochondrial dysfunction and oxidative stress in the development of SNHL caused by genetic mutations, aging, exposure to excessive noise, and ototoxic drugs. We also explore the advancements in antioxidant therapies for the different forms of acquired SNHL that are being evaluated in preclinical and clinical studies.
Noise-induced hearing loss is one of the most common forms of sensorineural hearing loss, is a major health problem, is largely preventable and is probably more widespread than revealed by ...conventional pure tone threshold testing. Noise-induced damage to the cochlea is traditionally considered to be associated with symmetrical mild to moderate hearing loss with associated tinnitus; however, there is a significant number of patients with asymmetrical thresholds and, depending on the exposure, severe to profound hearing loss as well.
Recent epidemiology and animal studies have provided further insight into the pathophysiology, clinical findings, social and economic impacts of noise-induced hearing loss. Furthermore, it is recently shown that acoustic trauma is associated with vestibular dysfunction, with associated dizziness that is not always measurable with current techniques. Deliberation of the prevalence, treatment and prevention of noise-induced hearing loss is important and timely. Currently, prevention and protection are the first lines of defence, although promising protective effects are emerging from multiple different pharmaceutical agents, such as steroids, antioxidants and neurotrophins.
This review provides a comprehensive update on the pathophysiology, investigations, prevalence of asymmetry, associated symptoms, and current strategies on the prevention and treatment of noise-induced hearing loss.
Sudden Sensorineural Hearing Loss Kuhn, Maggie; Heman-Ackah, Selena E.; Shaikh, Jamil A. ...
Trends in amplification,
09/2011, Volume:
15, Issue:
3
Journal Article
Peer reviewed
Open access
Sudden sensorineural hearing loss (SSNHL) is commonly encountered in audiologic and otolaryngologic practice. SSNHL is most commonly defined as sensorineural hearing loss of 30dB or greater over at ...least three contiguous audiometric frequencies occurring within a 72-hr period. Although the differential for SSNHL is vast, for the majority of patients an etiologic factor is not identified. Treatment for SSNHL of known etiology is directed toward that agent, with poor hearing outcomes characteristic for discoverable etiologies that cause inner ear hair cell loss. Steroid therapy is the current mainstay of treatment of idiopathic SSNHL in the United States. The prognosis for hearing recovery for idiopathic SSNHL is dependent on a number of factors including the severity of hearing loss, age, presence of vertigo, and shape of the audiogram.
Sudden sensorineural hearing loss (SSNHL) is a medical emergency, making detailed examination to determine possible causes and early treatment important. However, etiological examinations in SSNHL do ...not always reveal a cause, and several factors have been found to affect treatment outcomes. Various studies are being performed to determine the prognosis and effects of treatment in patients who experience sudden hearing loss, and to identify biomarkers associated with this condition. Embase, PubMed, and the Cochrane database were searched using the key words SSNHL, prognostic, and biomarker. This search identified 4 articles in Embase, 28 articles in PubMed, and 36 in the Cochrane database. Of these 68 articles, 3 were duplicates and 37 were unrelated to the research topic. After excluding these articles, the remaining 28 articles were reviewed. Factors associated with SSNHL were divided into six categories: metabolic, hemostatic, inflammatory, immunologic, oxidative, and other factors. The associations between these factors with the occurrence of SSNHL and with patient prognosis were analyzed. Low monocyte counts, low neutrophil/lymphocyte ratio (NLR) and monocyte/high-density lipoproteins (HDL) cholesterol ratio (MHR), and low concentrations of fibrinogen, platelet glycoprotein (GP) IIIa, and TNF-α were found to be associated with good prognosis. However, these factors alone could not completely determine the onset of and recovery from SSNHL, suggesting the need for future basic and clinical studies.
This study aims to evaluate the etiology of pediatric sensorineural hearing loss (SNHL). A total of 423 children with SNHL were evaluated, with the focus on the determination of causative genetic and ...acquired etiologies of uni- and bilateral SNHL in relation to age at diagnosis and severity of the hearing loss. We found that a stepwise diagnostic approach comprising of imaging, genetic, and/or pediatric evaluation identified a cause for SNHL in 67% of the children. The most common causative finding in children with bilateral SNHL was causative gene variants (26%), and in children with unilateral SNHL, a structural anomaly of the temporal bone (27%). The probability of finding an etiologic diagnosis is significantly higher in children under the age of 1 year and children with profound SNHL.
Conclusions
: With our stepwise diagnostic approach, we found a diagnostic yield of 67%. Bilateral SNHL often has a genetic cause, whereas in unilateral SNHL structural abnormalities of the labyrinth are the dominant etiologic factor. The diagnostic yield is associated with the age at detection and severity of hearing loss: the highest proportion of causative abnormalities is found in children with a young age at detection or a profound hearing loss.
What is Known:
• Congenital sensorineural hearing loss is one of the most common congenital disorders
• Determination of the cause is important for adequate management and prognosis and may include radiology, serology, and DNA analysis
What is New:
• Using a stepwise diagnostic approach, causative abnormalities are found in 67% both in uni- and bilateral SNHL, with the highest diagnostic yield in very young children and those suffering from profound hearing loss
• Bilateral SNHL often has a genetic cause, whereas in unilateral SNHL structural abnormalities of the labyrinth are the dominant etiologic factor
Summary Objectives Singers and voice teachers are exposed to a range of noise levels during a normal working day. This study aimed to assess the hearing thresholds in a large sample of generally ...healthy professional voice teachers and voice students to determine the prevalence of hearing loss in this population. Study Design A cross-sectional study was carried out. Methods Voice teachers and vocal students had the option to volunteer for a hearing screening of six standard frequencies in a quiet room with the Shoebox audiometer (Clearwater Clinical Limited) and to fill out a brief survey. Data were analyzed for the prevalence and severity of hearing loss in teachers and students based on several parameters assessed in the surveys. All data were analyzed using Microsoft Excel (Microsoft Corp.) and SPSS Statistics Software (IBM Corp.). Results A total of 158 participants were included: 58 self-identified as voice teachers, 106 as voice students, and 6 as both. The 6 participants who identified as both, were included in both categories for statistical purposes. Of the 158 participants, 36 had some level of hearing loss: 51.7% of voice teachers had hearing loss, and 7.5% of voice students had hearing loss. Several parameters of noise exposure were found to positively correlate with hearing loss and tinnitus ( P < 0.05). Years as a voice teacher and age were both predictors of hearing loss ( P < 0.05). Conclusions Hearing loss in a cohort of voice teachers appears to be more prevalent and severe than previously thought. There is a significant association between years teaching and hearing loss. Raising awareness in this population may prompt teachers and students to adopt strategies to protect their hearing.
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