Incidence of cochlear involvement in hyperbilirubinemic deafness

Assessment of Hearing Impairment in Sick Newborns: A Prospective Observational Study

BACKGROUND

 Undiagnosed neonatal hearing loss causes severe language, cognitive, and behavioral problems in children. Sick newborns who spend 48 hours in the neonatal intensive care unit (NICU) have a 10- to 20-fold increased risk of permanent hearing loss. The aim of this study is to identify hearing impairment in high-risk sick newborns who spend at least 48 hours in the NICU.

METHODS

 The present prospective observational study was conducted at a single center. All sick neonates admitted to the NICU for a minimum of 48 hours at the JK Lon Hospital, Zanana Hospital, and Mahila Chikitsalaya, Sawai Man Singh (SMS) Medical College, Jaipur, Rajasthan, India, from June 2017 to May 2018 were considered eligible for the study. The primary outcome was the assessment of hearing loss of high-risk newborns using otoacoustic emissions at the time of discharge, six weeks of age, and automated auditory brainstem response (AABR) at three months of chronological age. The secondary outcome was to analyze the association of hearing loss with different risk factors in high-risk neonates.

RESULTS

 A total of 150 infants who had one or more risk factors were studied, 60 were female and 90 were male. No statistically significant difference in hearing loss was observed based on birth weight, sex, and gestational age. The first distortion-product otoacoustic emission (DPOAE) screening was done on infants at the time of discharge from the NICU. Eighty-three infants (55.33%) had "refer" on the first DPOAE and the remaining 67 (44.67%) were passed results at the time of discharge. At six weeks of life, on repeat screening with a second DPOAE test, 36% "refer" on the first screen had a "refer" result on the second DPOAE. However, 4.4% "pass" on the first screen turned out to be "refer" on the second screen. These 33 infants who had "refer" results on the second screen were subjected to testing. At 10 weeks of life, AABR was performed on 33 infants. Eleven infants out of 33 had sensorineural hearing loss (SNHL) on AABR. Hearing impairment with the DPOAE test was observed with risk factors neonatal hyperbilirubinemia (NHH), hypoxic ischemic encephalopathy (HIE), and very low birth weight (VLBW) and was statistically significant among all risk factors. But, no such association (between hearing impairment and risk factors) was observed with the AABR test. In our study, we found that the duration of mechanical ventilation in mean days 7.67±6.24 had statistically significant SNHL compared to the lesser duration of mechanical ventilation (p<0.001).

CONCLUSION

Two-stage DPOAE done prior to AABR is helpful in the early detection of hearing loss.

Deafness in an auditory specialist, the big brown bat (Eptesicus fuscus)

Bats are long-lived animals that show presumed resistance to noise-induced and age-related hearing loss, which has been attributed to their dependence on sound processing for survival. Echolocation and basic auditory functions have been studied extensively in the big brown bat (Eptesicus fuscus), an insectivorous microchiropteran species. We conducted hearing tests and analysis of cochlear sensory cells in a group of big brown bats that exhibited anomalies in behavioral sonar tracking experiments and/or lacked neural responses to acoustic stimulation in subcortical auditory nuclei. We show for the first time the presence of profound deafness and extensive cochlear damage in an echolocating bat species. Auditory brainstem responses were abnormal or absent in these bats, and histological analyses of their cochleae revealed extensive loss of hair cells, supporting cells, and spiral ganglion neurons. The underlying cause of deafness is unknown.

Bilirubin-induced neurotoxic and ototoxic effects in rat cochlear and vestibular organotypic cultures

Exposure to high levels of bilirubin in hyperbilirubinemia patients and animal models can result in sensorineural deafness. However, the mechanisms underlying bilirubin-induced damage to the inner ear, including the cochlear and vestibular organs, remain unknown. The present analyses of cochlear and vestibular organotypic cultures obtained from postnatal day 3 rats exposed to bilirubin at varying concentrations (0, 10, 50, 100, or 250 μM) for 24 h revealed that auditory nerve fibers (ANFs) and vestibular nerve endings were destroyed even at low doses (10 and 50 μM). Additionally, as the bilirubin dose increased, spiral ganglion neurons (SGNs) and vestibular ganglion neurons (VGNs) exhibited gradual shrinkage in conjunction with nuclei condensation or fragmentation in a dose-dependent manner. The loss of cochlear and vestibular hair cells (HCs) was only evident in explants treated with the highest concentration of bilirubin (250 μM), and bilirubin-induced major apoptosis most likely occurred via the extrinsic apoptotic pathway. Thus, the present results indicate that inner ear neurons and fibers were more sensitive to, and exhibited more severe damage following, bilirubin-induced neurotoxicity than sensory HCs, which illustrates the underlying causes of auditory neuropathy and vestibulopathy in hyperbilirubinemia patients.

Auditory evoked potentials in a newborn Wistar rat model of hyperbilirubinemia

Introduction

Hyperbilirubinemia is a common health problem in newborns. Its effects can be different according to the level and duration of the hyperbilirubinemia. The toxic effect of bilirubin on the auditory system can be seen as a sensory neural hearing loss or auditory neuropathy spectrum disorder (ANSD).

Objective

The purpose of our study was to determine the effects of toxic bilirubin level on the auditory system by using Auditory Brainstem Response audiometry.

Methods

Rats are used as animal models due to their low cost and easy attainability. Auditory Brainstem Response was used for auditory assessment. In this study, three groups were established: experimental, control and placebo groups.

Results

In the experimental group, which consists of rats with hyperbilirubinemia, sensory neural hearing loss was found bilaterally in 4 rats (66.67%) and unilaterally in 2 rats (16.67%) and auditory neuropathy spectrum disorder was found unilaterally in 1 rat (8.33%). Auditory Brainstem Response thresholds were significantly elevated compared to control and placebo groups (p < 0.05).

Conclusion

Hyperbilirubinemia of newborn rats may result both in sensory neural hearing loss and auditory neuropathy spectrum disorder.

Risk Factors for Sensorineural Hearing Loss Among High-Risk Infants in Golestan Province, Iran in 2010 - 2011

Background:

Hearing impairment, as one of the most common birth defects, is a hidden disability with negative impacts on speech and cognitive development.

Objectives:

The aim of this study was to assess the prevalence of sensorineural hearing loss (SNHL) and determine the associated risk factors among infants admitted to neonatal intensive care units (NICUs) and neonatal wards of teaching hospitals, affiliated to Golestan University of Medical Sciences, Gorgan, Iran.

Patients and Methods:

In this cross-sectional study, 791 infants were recruited via non-random sampling. Demographic and clinical characteristics of the subjects were gathered, and the Automated Auditory Brainstem Response (AABR) test was performed upon admission. Afterwards, the subjects were followed-up and re-assessed, using the AABR test. For infants with abnormal AABR results, the Auditory Brainstem Response (ABR) test was performed on the day of discharge.

Results:

The mean age of the infants was 3.75 ± 4.86 days upon admission, and 56.4% of the subjects were female. The mean length of hospital stay was 9.63 ± 1.1 days; the subjects were hospitalized for 3.50 ± 10.21 days in the NICUs and 6.1 ± 5.27 days in the neonatal wards. In total, 3.4% of the infants presented with SNHL. No significant difference was found between SNHL and neonates’ age (P = 0.52), sex (P = 0.5), or sepsis (P = 0.94). However, SNHL was significantly associated with gestational age (P = 0.045), birth weight (P < 0.001), length of hospital stay (P < 0.001), pathological jaundice (P=0.033), antibiotic treatments (P = 0.007), and total serum bilirubin level (P = 0.01). Additionally, binary logistic regression analysis demonstrated the association between SNHL and these factors.

Conclusions:

In this study, the prevalence of SNHL among hospitalized neonates was similar to previous reports in Iran and other countries. Based on the findings, administration of ototoxic drugs during the neonatal period can lead to SNHL. Therefore, it seems essential to regularly screen newborns under treatment and limit the indiscriminate use of ototoxic drugs.

2014 CODEPEH recommendations: Early detection of late onset deafness, audiological diagnosis, hearing aid fitting and early intervention

The latest scientific literature considers early diagnosis of deafness as the key element to define the educational and inclusive prognosis of the deaf child, because it allows taking advantage of the critical period of development (0-4 years). Highly significant differences exist between deaf people who have been stimulated early and those who have received late or improper intervention. Early identification of late-onset disorders requires special attention and knowledge on the part of every childcare professional. Programs and additional actions beyond neonatal screening should be designed and planed to ensure that every child with a significant hearing loss is detected early. For this purpose, the CODEPEH would like to highlight the need for continuous monitoring of children's auditory health. Consequently, CODEPEH has drafted the recommendations included in the present document.

Hearing and neurological impairment in children with history of exchange transfusion for neonatal hyperbilirubinemia

The objective was to determine frequency of sensorineural hearing loss (SNHL), identified by abnormal threshold in evoked potentials, absence of otoacoustic emissions and behavioral responses, auditory neuropathy (AN) (absence of evoked potentials, with preservation of otoacoustic emissions), and neurological comorbidity in infants with hyperbilirubinemia (HB) treated with exchange-transfusion (ET). From a total of 7,219 infants, ET was performed on 336 (4.6%). Inclusion criteria were fulfilled in 102; 234 children did not meet criteria (182 outside of the study period, 34 did not have complete audiological evaluation, and 18 rejected the followup). Thirty-five children (34%) were born at-term and 67 (66%) were preterm. Children had a mean age of 5.5 ± 3.9 years. Main causes of ET were Rh isoimmunization in 48 (47%), ABO incompatibility in 28 (27.5%), and multifactorial causes in 26 (25.5%). Fifteen (15%) children presented with SNHL. Preterm newborns presented more often with SNHL. Indirect bilirubin level was higher in children with SNHL (22.2 versus 18.7 mg/dL, P = 0.02). No cases of AN were documented. An increased risk of neurologic sequelae was observed in children with SNHL. In conclusion, we disclosed a high frequency of SNHL in children with neonatal HB and ET and neurological alterations. No cases of AN were observed.

Bilirubin induces auditory neuropathy in neonatal guinea pigs via auditory nerve fiber damage

Bilirubin can cause temporary or permanent sensorineural deafness in newborn babies with hyperbilirubinemia. However, the underlying targets and physiological effects of bilirubin-induced damage in the peripheral auditory system are unclear. Using cochlear functional assays and electron microscopy imaging of the inner ear in neonatal guinea pigs, we show here that bilirubin exposure resulted in threshold elevation in both compound action potential (CAP) and auditory brainstem response (ABR), which was apparent at 1 hr and peaked 8 hr after drug administration. The threshold elevation was associated with delayed wave latencies and elongated interwave intervals in ABR and CAP. At 72 hr postinjection, these measures returned to control levels, except for the CAP amplitude. Cochlear microphonics remained unchanged during the experiment. Morphological abnormalities were consistent with the electrophysiological dysfunction, revealing fewer auditory nerve fibers (ANFs) in the basal turn, myelin sheath lesions of spiral ganglion neurons (SGNs) and ANFs, and loss of type 1 afferent endings beneath inner hair cells (IHCs) without loss of hair cells at 8 hr posttreatment. Similar to the electrophysiological findings, morphological changes were mostly reversed 10 days after treatment, except for the ANF reduction in the basal turn. These results suggest that hyperbilirubinemia in neonatal guinea pigs impaired auditory peripheral neuromechanisms that targeted mainly the IHC synapses and the myelin sheath of SGNs and their fibers. Our observations indicate a potential connection between hyperbilirubinemia and auditory neuropathy.

Risk factor analysis for late-onset neonatal hyperbilirubinemia in Taiwanese infants

BACKGROUND

Neonatal hyperbilirubinemia is a recognized health risk for newborns. It can cause kernicterus and hearing impairment. Certain groups of infants who do not have significant jaundice during the first few days of life develop hyperbilirubinemia later. Because early discharge is a worldwide trend, prompt identification of this group of infants is of paramount importance in preventing complications.

METHODS

The data used were derived from a medical center. A total of 523 term or near-term infants were enrolled in this study. All infants were scheduled for follow-up visits. In this study, late-onset neonatal hyperbitirubinemia was defined as a total bilirubin level greater than 15 mg/dL, or receiving phototherapy at 5-7 days. Newborns that had clinically significant jaundice within 96 hours of life were excluded from analysis. Univariate and multivariate logistic regressions were applied for statistical analysis.

RESULTS

One hundred and eighty infants were included for data analysis. Thirty-nine (21.7%) had late onset hyperbilirubinemia. Exclusive breast-feeding and less body weight loss during the 1st day of life were both significant risk factors for late onset hyperbilirubinemia. However, early discharge was not associated with late-onset hyperbilirubinemia.

CONCLUSION

Thirty-nine (21.7%) infants develop late hyperbilirubinemia at the age of one week. Exclusive breast-feeding and less body weight loss were significant risk factors. Follow-up visits are recommended for all infants, especially for those who have these risk factors.

Analysis of transient otoacoustic emissions and brainstem evoked auditory potentials in neonates with hyperbilirubinemia

Hyperbilirubinemia is toxic to the auditory pathways and to the central nervous system, leaving sequelae such as hearing loss and encephalopathy.

Aim

to assess the hearing of neonates with hyperbilirubinemia, using transient evoked otoacoustic emissions (TOAEs) and brainstem evoked auditory potentials (BEAP). Prospective study.

Materials and Methods

we had two groups: GI (n-25), neonates with hyperbilirubinemia; GII (n-22), neonates without hyperbilirubinemia and without risk factors for hearing loss. All the neonates had up to 60 days of life and were submitted to TOAE and BEAP.

Results

12 neonates from GI and 10 from GII were girls and 13 from GI and 12 from GII were boys. TOAEs were present in all the children, however with lower amplitudes in GI, especially in the frequencies of 2 and 3KHz (p < 0.05). Regarding the BEAP, we observed a mild PV and LI-V increase in BI. The alterations observed in these tests do not correlate to the serum levels of bilirubin.

Conclusions

in neonates with hyperbilirubinemia, we noticed lower TOAE amplitudes and mild PV and LI-V increase, indicating cochlear and retrocochlear disorders, stressing the importance of using both tests and carefully reading them in these evaluations.

Editorial: 'auditory neuropathy' and cochlear implantation - myths and facts

A review of current opinion concerning 'auditory neuropathy' is presented. It is suggested that electrophysiological tests, including electrocochleography, auditory brainstem responses and electrically evoked auditory brainstem responses, together with imaging, can provide information regarding the site of the underlying pathological conditions that may produce the combination of otoacoustic emissions in the absence of auditory brainstem responses in children with hearing loss. It is suggested that in 75% of cases auditory neuropathy can merely be a result of surviving outer hair cells when inner hair cell function is compromised. The remaining cases of auditory neuropathy may have dysfunction of the afferent neural synapse, cochlear nerve, cochlear nucleus, auditory brainstem tracts and central auditory system. Rather than continuing to use a blanket and often misleading term, we are now in a better position to describe each individual case exhibiting this phenomenon according to the correct site of lesion.

Etiologies of hearing impairment among infants and toddlers: 1986-1987 versus 2001

OBJECTIVE

This study compares etiological factors for hearing loss, relevant neuro-sensory impairments and demographics between two groups of children referred for early hearing habilitation in Israel. Group I was referred in the years 1986-1987 (n=73) and group II was referred during 2001 (n=73).

METHODS

Family history, pregnancy, risk factors, developmental milestones, medical history, auditory brainstem response, tympanometry, otoacoustic emissions and behavioral audiometric results were retrospectively retrieved in 2003 from medical records at the MICHA Society for Deaf Children in Israel.

RESULTS

New referrals per year have doubled themselves over the 15 years that elapsed between 1986-1987 and 2001. No changes in gender and age at time of admission were found. The prevalence of mild-to-moderate hearing loss was higher in Group II while severe and profound hearing loss was more prevalent in Group I. Assisted reproductive technologies were involved only in Group II. There were more twin births and post-natal hypoxia in Group II. Rh incompatibility was reported only in Group I. Severe hearing loss was associated with younger age at admission. No significant associations were found between age at admission and etiology with the exception of the fact that children with genetic background were admitted at an earlier age. Since no significant association between genetic background and severity of hearing loss was found, it is conclude that the association between severity of hearing loss and age at admission did not account for changes in etiology in our sample.

CONCLUSIONS

Classic risk factors for hearing loss among infants and toddlers have not changed much over time, and the few changes that have been noticed are probably due to expanded medical knowledge and improved technologies.

Transient Deafness in Young Candidates for Cochlear Implants

This study describes 5 infants who were diagnosed with auditory neuropathy (AN) associated with severe to profound neural hearing loss shortly after birth. However, on repetition of the tests 7-12 months later, all infants showed full or partial recovery. The follow-up electrophysiological patterns were characterized by the appearance of wave I, followed by wave III and V, reflecting synchronization of auditory pathways and improvement in auditory nerve function. Suspected causative or contributory factors were neonatal hyperbilirubinemia, hypoxia, ischemia, and central nervous system immaturity, alone or in combination. These findings indicate that lack of an auditory brain stem response does not necessarily mean no hearing and that the situation where AN exists can improve. Thus, clinicians should be made aware that although cochlear implants may yield better auditory performance when applied early, they should be considered a therapeutic option only after repeated measures have proved persistent AN, and no child should be considered for an implant until a behavioral measure of hearing has been obtained.

Benefits and challenges of newborn hearing screening for developing countries

The late detection of permanent congenital and early-onset hearing loss (PCEHL) often has severe effects on linguistic, speech, cognitive and educational development in affected children. Since newborn hearing screening (NHS) allows most PCEHL to be detected early enough for optimal intervention, the prospects of its introduction in the developing world are reviewed in this paper. It is observed that a simple generalisation on the feasibility of NHS for the developing countries seems inappropriate in view of the diversities in the health and socio-economic status of these countries and the recent favourable reports of universal newborn hearing screening from the region. NHS empowers parents to make timely choices that will allow their hearing impaired children to be given a good start in life and be fully integrated into the wider community. It also compels attention towards the development of essential hearing healthcare services, besides the specific documented benefits. Existing child-healthcare structures such as the expanded programme on immunisation (EPI), baby friendly hospital initiatives (BFHI) and integrated management of childhood illness (IMCI) provide opportunities for the introduction of some form of NHS in many of these countries where routine or systematic childhood hearing screening does not exist. Limited funding, manpower shortages, inadequate support services, low public awareness and the uncertainty regarding the commitment from healthcare practitioners may present some challenges but these are not insurmountable. Pilot studies are necessary in each country to provide empirical data that will guide healthcare providers who wish to introduce such a programme at any level of healthcare delivery.

Otoacoustic emissions

PURPOSE OF REVIEW

Otoacoustic emissions offer the practitioner a number of beneficial features as a noninvasive and objective measure of the ear's ability to process acoustic stimuli.

RECENT FINDINGS

Since their discovery, a number of clinical applications of otoacoustic emissions have been established, including their utility in the differential diagnosis of sensorineural hearing loss, in the screening of cochlear function in infants and other difficult-to-test patients, and in the monitoring of outer hair cell healthiness in patients who are exposed to potentially damaging agents or who have progressive hearing ailments.

SUMMARY

Clinical applications of OAEs have developed very rapidly and OAEs have become the standard of care, at least, for pediatric patients.