Longitudinal study of hearing-disabled children. A follow-up investigation

Childhood sensorineural hearing loss: effects of combined exposure with aging or noise exposure later in life

The aim of the study was to examine childhood high-frequency sensorineural hearing loss (HF-SNHL) and the effects of combined exposure with aging or noise exposure on HF hearing thresholds in adulthood. Population-based cohort study of 30,003 adults (mean age 40 years) underwent an audiometry and completed a hearing questionnaire. At age 7-13 years, the same people had participated in a longitudinal school hearing investigation, in which 283 participants were diagnosed with HF-SNHL [PTA 3-8 kHz ≥ 25 dB HL (mean 45 dB HL), worse hearing ear], and 29,720 participants had normal hearing thresholds. The effect of childhood HF-SNHL on adult hearing threshold was significantly moderated by age. Age stratified analyses showed that the difference in HF hearing thresholds between adults with and without childhood HF-SNHL was 33 dB (95 % CI 31-34) in young adults (n = 173, aged 20-39 years) and 37 dB (95 % CI 34-39) in middle-aged adults (n = 110, aged 40-56 years). The combined exposure of childhood HF-SNHL and noise exposure showed a simple additive effect. It appears to be a super-additive effect of childhood-onset HF-SNHL and aging on adult hearing thresholds. An explanation might be that already damaged hair cells are more susceptible to age-related degeneration. To exclude possible birth cohort effects, the finding should be confirmed by a study with several audiometries in adulthood.

Longitudinal study of hearing impairment in children

The aim of this study is to evaluate the frequency of progression in permanent childhood hearing impairment (PHI) and to relate potential specific factors to the eventual progression. A description is made of the true longitudinal hearing thresholds in four groups of children according to different observation periods and being part of a prospective pediatric audiological registry-based study established in 1989. At the time of data collection the registry included 1373 children born after 1/1-1970 with a PHI > 20 dB in either the right or the left ear at any pure tone frequency. The children were subdivided according to the following observation periods: 1-3 years (N=266), >3-5 years (N=148), >5-10 years (N=212) and >10 years (N=62). The differences from the first to the most recent audiometric thresholds were analysed for the right and left ears separately, at the pure tone frequencies 250, 500, 1000, 2000, 4000 and 8000 Hz, for the average of 500, 1000, 2000 and 4000 Hz, for the average of 2000 and 4000 Hz and for the average of 4000 and 8000 Hz. Those showing a progression >15 dB for the average across 500-4000 Hz were analysed for age at onset and aetiology of hearing impairment, showing that genetic factors are predominant in progressive PHI. It was also found that progression in PHI is most frequent in early childhood but found only in 5.7% after the age of 4 years.

Adverse perinatal conditions and the inner ear

Epidemiological studies in a number of Western countries have attributed 6-14% of sensorineural hearing impairment from birth or early childhood to problems relating to the birth process [1-4]. In spite of this association it is not always clear in individual instances whether adverse perinatal conditions identified subsequently have been causative of a hearing loss or not. It is possible that the hearing impairment was the consequence of an earlier intrauterine insult or is a coincidental finding. Infants carrying genetic mutations for hearing loss may coincidentally experience perinatal stress. It is therefore important to investigate the cause of a hearing loss discovered in infancy irrespective of the history of the infant having experienced adverse conditions surrounding the time of birth.

Causes of hearing impairment in deaf pupils with a mental handicap

An aetiological study was performed on 122 deaf pupils (57 aged < 20 years, 65 aged > 20 years) at the Institute for the Deaf in Sint-Michielsgestel, The Netherlands. Besides hearing impairment with thresholds of > 60 dB HL, all the participants had a mental handicap with a non-verbal IQ of 40-80. Sixteen per cent of them were of non-Dutch origin. The cause of hearing impairment was acquired in 48%, inherited in 17%, chromosomal in 4% and unknown in 30%. In comparison with other studies on the aetiology of childhood deafness, acquired causes predominated over inherited causes, which may be typical of deafness combined with a mental handicap. We found a significant predominance of non-Dutch pupils among the rubella aetiology cases and male predominance among the hearing impaired pupils in general.

Minimal, progressive, and fluctuating hearing losses in children. Characteristics, identification, and management

Referring to specific types of hearing loss as "minimal" or "mild" seems to imply that their effects are equally mild or negligible. A growing body of literature, however, supports the notion that such losses can have a significant impact on the communicative and educational development of young children. Although OME is considered a common childhood ailment, mounting evidence suggests that it is not always benign and may contribute to significant educational and communicative difficulties in some young children when accompanied by conductive hearing loss. Even very mild bilateral and unilateral SNHL seems to contribute to problems in the areas of social and emotional function, educational achievement, and communication in some children. Because these hearing losses are so mild, they may not be immediately recognized as the source of such difficulties. The purpose of this report is to heighten the general pediatrician's awareness of the significance of even very mild or minimal hearing losses in children. As the gatekeepers for children's health care, pediatricians are typically the primary recipients of parental expressions of concern and the initiators of evaluations or referrals to address such.

Prevalence and etiology of bilateral sensorineural hearing impairment in a Finnish childhood population

A retrospective study was performed on the prevalence and etiology of bilateral sensorineural hearing impairment (> 25 dB at 0.5-4 kHz in the better ear) among children born 1974-1987 in a province of eastern Finland. A total of 98 children with hearing impairment were identified, which gave a prevalence of 2.1 per 1000 live births. This prevalence was higher than reported form most of other developed countries but slightly lower than reported from Sweden. A slight decline from the prevalence of 2.3 per 1000 in the 1970s to the prevalence of 1.9 per 1000 in the 1980s was observed. Contrary to several earlier studies, no male predominance was noted, there were even slightly more females than males (52 vs. 46). Etiology of the hearing loss was estimated to be genetic in 41%, congenital nongenetic in 13%, delayed-onset nongenetic in 16% and remained unknown in 30%. On average, children with a congenital disorder had more severe hearing impairment than those with delayed-onset hearing loss, e.g. 31% of the former patients had profound (> 95 dB) hearing loss compared to 6% of the latter. A very gratifying finding was that no case of congenital hearing impairment caused by maternal rubella was identified after 1982, obviously due to general vaccinations. Also, a decline in cases of hearing loss attributed to perinatal and neonatal complications was observed.

Profound permanent hearing impairment in childhood: causative factors in two European countries

A collaboration between Denmark and Wales was established in order to evaluate any differences between countries in factors causing permanent childhood hearing impairment (PCHI). Two identical 6-year birth-cohorts from 1975-1980 suffering from a permanent hearing loss > or = 90 dB HL in the better hearing ear, averaged across 0.5-4 kHz (BEHL), were included in the analysis. The overall estimated prevalence of children with this loss was 0.41/live births in Wales (n = 59). In Denmark the overall prevalence was 0.45/1,000 live births (n = 34), there being no significant differences in prevalence between the two countries. Both cohorts were subjected to a multidisciplinary investigation protocol. No significant differences were found between countries in the proportion of hearing impairment caused by the various factors, when based on uniform criteria and identical birth-cohorts. The proportion of inherited hearing loss is 47-50% in the two countries. Within inheritance the proportion of non-syndromal/syndromal inheritance differs slightly, as non-syndromal inheritance comprises 50% in Wales, and 76% in Denmark. The reported proportion of 16-34% of unknown factors causing profound PCHI emphasises the need for appropriate protocols for aetiological evaluation.

Risk factors for childhood sensorineural hearing loss in the Oxford region

We have used a comprehensive register of hearing-impaired children born in the former Oxford Health Region to study risk factors for sensorineural hearing loss. The occurrence of a wide variety of risk factors was documented from the case notes of 145 children; these were all the cases known at the time of the study with all degrees of hearing loss born between 1984 and 1988. Comparison with the normal Regional population showed that maternal age over 35 years and Asian ethnic origin were significant risk factors for congenital (non-acquired) hearing loss (odds ratio 1.7 and 2.5 respectively). Black/Asian children were also significantly more likely to have acquired losses. Low birthweight (below 2500 g) also gave a significantly increased risk, with an odds ratio of 4.5, rising to 9.6 for birthweight less than 1500 g. We also found that significantly more hearing-impaired cases were in lower social classes compared with the general population. A high proportion of cases (24%) had cranio-facial abnormalities (CFA), including many non-aural abnormalities and dysmorphic features, which therefore should be counted as high risk. Hearing losses acquired due to perinatal causes were almost all mild or moderate. Four factors-admission to special care baby unit for more than 72 hours, CFA, family history, and meningitis-accounted for 69% of all cases in this study. Targeted neonatal screening based on the first three factors, plus obligatory testing following meningitis, therefore, should be highly efficient at detecting deafness early.

Epidemiology of permanent hearing impairment in children in relation to costs of a hearing health surveillance program

The objective of this investigation was to estimate the prevalence of any permanent hearing impairment (PHI) in the right and or left ear based on children included into a surveillance program in the local pediatric hearing health services (PHHS), and to analyze the costs, generated by the children. The study is a cross-sectional study, which is part of a major prospective study directed towards delineation of all aspects of pediatric audiology. The present sample comprises 228 children, 115 males and 113 females, at a median age of 13 years, range 0-24, and involves all children living in the health district of the City of Copenhagen, who are or have been included in a local surveillance program with one (school children) or two (pre-school children) annual visits for children with PHI > 20 dB HL at any frequency in either the left or the right ear. The prevalence of PHI increases with increasing age, reaching its peak in the age band 10-14 years exhibiting a rate of 5.32 1000 (95% confidence intervals: 4.27 to 6.64 per 1000). The estimated incidence of PHI in a ten year cohort born 1977-1986 is 325 100 000 children born (95% confidence intervals: 277 to 382 per 100 000). The most frequent factor causing PHI is inheritance, showing an increase from 20% in 1977-1981 cohorts, to 37% in 1982-1986 cohorts. The costs involved in the PHHS concerning PHI varies considerably from approximately 345 000 to 990 000 DKr.. depending on the model used for the economical analysis. No data on cost-benefit or cost-effectiveness can be given in this context, and it is concluded that the documented changes in the prevalence and causes of PHI in children emphasize the need for a continuous monitoring and evaluation of the epidemiological figures.

The causes of profound hearing impairment in a school for the deaf--a longitudinal study

The study was aimed towards an evaluation of the causes of hearing loss in children attending the School for the 'Deaf' in Copenhagen in 1993-4 in comparison to causes evaluated 10 and 40 years previously (Arnvig, 1953; Holten and Parving, 1985). The 124 children attending the school in 1993 represent 0.04% of the age-matched target population of 312,715. A more detailed evaluation of two comparable cohorts born in 1969-77 and 1979-87 demonstrates a significant increase of children attending this type of school from 0.03% to 0.05% within a 10-year period, while a comparison between 1953 and 1993 demonstrates a reduction from 0.07% to 0.04%. The longitudinal evaluation of the causes of hearing loss showed a significant increase in the frequency of congenital inherited hearing impairment from 29% (1953) through 33% (1983) to 43% (1993), whereas a significant reduction of about 17% in the frequency of acquired deafness due to chronic otitis media was found. Between 1953 and 1993 a minor reduction (2%) in post-meningitic acquired hearing impairment was found, between 1953 and 1983 there was a significant increase in prenatal infections, compared with a decrease of 6% between 1983 and 1993. It is concluded that significant changes are found both in the prevalence of children referred to the school and in the factors causing severe to profound hearing impairment in children. Continuous recording of, and improvement in, diagnostic classification is necessary to obtain preventive measures.

Hearing disability in childhood--a cross-sectional and longitudinal investigation of causative factors

This contribution describes and compares the causes of hearing disability in a cohort of children, born 1980-90, provided with hearing aids and included into the longitudinal surveillance programs of hearing-disabled children performed in two pediatric audiological units within the Copenhagen area. In addition the causes of hearing disability in childhood are compared with the causes found in a cohort born 1970-80, within the same geographical area, using the same criteria for hearing disability and diagnostic classification. No significant differences in the etiology of hearing disability were present in the two districts, and in the combined area prenatal causes accounted for 55% with inheritance (46%) being the most prominent cause of hearing disability. A significant increase in the incidence of inherited hearing disability among the prenatal causes from 69% in the 1970-80 cohort to 85% in the 1980-90 cohort was demonstrated, while a significant decrease in the incidence of foetal infection (i.e. rubella) from 27% to 9% within the two decades was demonstrated. No significant changes in the perinatal and postnatal causes were found from the 1970-80 to 1980-90 cohort, and although an improvement in the diagnostic procedures was found--i.e. a reduction from 26% to 20% in the incidence of unknown cause--the difference in the incidence of unknown cause is insignificant between the two decades. The investigation supports the need for continuous monitoring of the causes of hearing disability in childhood and supports the potential value of worldwide accepted criteria for etiological categories.

Congenital hearing disability--epidemiology and identification: a comparison between two health authority districts

The objective of the present study was to describe some epidemiological aspects of congenital/early acquired (i.e. in the neonatal period) hearing disability (CEHD) in children born between 1980 and 1990, living in two separate health authority districts, i.e. the Copenhagen City/County; in addition, to evaluate the age at identification of the children, the persons raising suspicion of the hearing loss and the pattern of referral; finally, to compare some epidemiological aspects and the age at identification of similarly defined cohorts of children, born 1970-80. Thus the evaluation can be considered as an audit of the primary health care sector concerning children with CEHD. An identical prevalence rate of CEHD was demonstrated, i.e. 1.5/1000 with a better ear hearing level average at 0.5-4 kHz > or = 25 dB (BEHL 0.5-4 kHz) in both regions and unchanged from 1970-80. The median age at identification in the total cohort was 16/18 months in the City/County, respectively, demonstrating a significantly earlier identification of at-risk children in the County with the opposite pattern in the City. The parents were the first to raise suspicion of their child's hearing disability in 50%/57% in the City/County and only minor differences in the pattern of referral was found in the two regions. The frequency of at-risk children among parents/professionals who first suspected the CEHD showed no significant differences; however, the BEHL 0.5-4 kHz in the children was poorer in the group of parents who first raised the suspicion when compared with the group of professionals. Thus the BEHL 0.5-4 kHz is of significance for the age at identification and for the person raising the suspicion of CEHD. Although an improvement in the early identification of CEHD has taken place, when comparing the 1970-80 cohort and 1980-90 cohort, it is concluded that children with CEHD are identified with a substantial delay and that the line of information both concerning high-risk criteria and general information should be continued and intensified towards both parents and professionals.

Progressive hearing loss in hard-of-hearing children

A group of 92 children with bilateral sensorineural hearing loss has been followed up over a period of up to 15 years from the time that an initial reliable audiogram was obtained. This group was studied in order to determine the frequency of occurrence of progressive hearing loss and the relationship of the progressive to the presumed etiology of hearing loss. Progression of hearing loss was demonstrated in 21 children out of the 92 children studied. This progression of hearing loss was either bilateral or unilateral, and no evident relationship could be found between the presumed etiology of hearing loss and its progressivity.

Intervention and the hearing-impaired child--an evaluation of outcome

The investigation was performed in order to evaluate the outcome of intervention in preschool age. The material comprises a cohort of 138 children, 76 boys and 62 girls, born during 1970-1980, living in the Copenhagen County at the time of data collection (1987), all suffering from predominantly congenital/early acquired hearing disability (i.e. hearing level greater than or equal to 35 dB HL for the average of 0.5-4 kHz on the better hearing ear). The type of school attended is used as a measure for outcome of preschool intervention. It was demonstrated that 49% attended normal class (speech), 21% attended special units (total communication), and 24% attended the school for the deaf (sign/manual). By subdivision the children (n = 75) with a hearing loss less than 75 dB HL attended normal class in 80%; 7% attended special units. The children (n = 63) with hearing loss greater than or equal to 75 dB HL attended normal class in 11%, special units in 33%, and school for the deaf in 52%. An early identification of the hearing loss was found to facilitate attendance of normal class in the group with a hearing loss less than 75 dB HL. Among the children at the school for the deaf 84% had speaking parents. The frequency of the causes of hearing loss differs significantly in the special units, when compared to the total cohort. It is concluded that the outcome of preschool intervention is related predominantly to the degree of hearing loss; that an early intervention in the group of children with hearing loss less than 75 dB HL facilitates the attendance of normal class; that the frequency of the causes of hearing impairment is different in the special units.

Audiometric tests in gene carriers of Norrie's disease

The purpose of the present study was to validate the reliability of audiometric testing procedures in the identification of carriers of Norrie's disease by using DNA analysis. Potential female carriers of Norrie's disease were investigated by means of Békésy tracing audiometry and stapedial reflex thresholds previously found to reveal carriers of recessively inherited hearing impairment by means of peculiar 'dips' and elevation in the thresholds. Relating the audiometric test results to the outcome of the DNA analysis the previous findings could not be confirmed. In addition no concordance between the two audiometric test procedures was demonstrated, and Békésy threshold tracing exhibited poor repeatability and sensitivity. It is concluded that none of these audiometric test procedures are feasible for detection of carriers of an X-linked hearing disorder, such as Norrie's disease.