SENSORINEURAL HEARING LOSS IN CHILDREN

Hearing loss in infants and children may be sensorineural, conductive, or mixed; variable in severity from mild to profound; unilateral or bilateral; symmetric or asymmetric in audiometric configuration; syndromic (involving other identifiable features) or nonsyndromic (isolated hearing loss); congenital or postnatal (i.e., before, during, or after speech and language acquisition) in onset; attributable to genetic or nongenetic causes; characterized by stable, fluctuating, or progressive auditory thresholds; and coexistent with one or more developmental disabilities, such as learning problems or mental retardation. Absent obvious ear, head, or neck deformities, congenital hearing loss can present as an invisible disability at birth that may not be recognized until an infant fails to achieve expected communicative milestones. Persistent, congenital, or early-onset hearing loss in the moderate to profound range (41 to 100 dB) distorts the developing child's perception of his or her attempts at speech production and the speech of others. If educationally significant, bilateral hearing loss remains undetected through the critical language acquisition period during the first years of life, and the resultant impairment of receptive and expressive speech and language development can impede acquisition of literacy skills, school achievement, and social and emotional development. 6,33,52,77 Persistent unilateral hearing loss in the moderate to profound range typically had been regarded as developmentally innocuous for a school-aged child if appropriate compensatory strategies, such as preferential classroom seating, were implemented. Recent reports, however, link unilateral sensorineural hearing loss (SNHL) to poor academic performance, increased likelihood of repeating a grade, and school behavior problems. 7,13 In developed countries, 1.0 to 2.0 per 1000 school-aged children exhibit a bilateral SNHL of 50 dB or worse, including 0.5 to 1.0 per 1000 whose bilateral losses exceed 75 dB. 10 Data from the United Kingdom 25 indicate that 1 of 943 newborns followed longitudinally into school were subsequently confirmed to have a SNHL or mixed hearing loss. Children who were graduates of the neonatal intensive care unit (NICU) experienced increased risk for hearing loss (1/174 NICU infants versus 1/1278 non-NICU infants). Infants and children with lesser degrees of persistent hearing loss (i.e., "hard of hearing" versus deaf) are 5 to 10 times as numerous as those with severe to profound losses. 73,78 Unilateral sensorineural hearing loss (USNHL) of 45 dB or worse among US school-aged children has a prevalence rate of about 3 per 1000 children. 4 Assuming a stricter hearing loss criterion of 26 dB instead of 45 dB, the prevalence increases to 13 per 1000. No reliable prevalence data are available for infants and preschoolers because unilateral losses are generally discovered later in life than bilateral impairments (mean age in one study was 8.78 years). 13 Children with USNHL can experience impaired speech perception when background noise is presented to the better ear. Background noise in most elementary school settings approaches 50 dB to 70 dB sound pressure level (SPL), and unfavorable sound reverberation conditions compound problems in open classrooms. Early identification of educationally significant hearing loss has been targeted as a national health objective. 73 The 1993 National Institutes of Health (NIH) Consensus Statement on Early Identification of Hearing Impairment in Infants and Young Children 27 reported the average age of diagnosis of hearing loss in children with congenital or early-onset losses is an unacceptable 2.5 years. Previous early identification initiatives, including public awareness campaigns, mass screening questionnaires for completion after delivery, and a range of neonatal hearing screening techniques, have proven clinically unworkable or prohibitively expensive. The Joint Committee on Infant Hearing, 41 a multispecialty body including pediatricians, otolaryngologists, and audiologists, has issued a series of position statements enumerating risk indicators to facilitate identification of neonates at sufficiently increased risk for permanent hearing loss to warrant hearing screening. A shortcoming of such focused early identification programs is their failure to identify as many as 50% of children who manifest educationally significant hearing loss by elementary school age. Renewed interest in universal hearing screening of the 4 million infants born annually in the United States was stimulated by the introduction of reliable objective screening techniques using evoked otoacoustic emissions and automated auditory brainstem response (ABR) measures. The NIH Consensus Statement on Early Identification of Childhood Hearing Loss 27 recommends in-hospital hearing screening for all infants admitted to NICUs and screening of all other infants within the first 3 months of life. Evoked otoacoustic emission measures were recommended for initial screening, with all failures being rescreened with ABR. Infants failing rescreening should be referred promptly for comprehensive audiologic evaluation. The 1994 Position Statement of the Joint Committee on Infant Hearing 41 endorses the goal of universal detection of infants with hearing loss as early as possible. It also addresses the need to identify infants with SNHL having onset after 3 months of age. While the Joint Committee endorsed the goal of universal detection, it also outlined a strategy for clinical settings in which universal screening has not been implemented. The Position Statement includes an expanded list of indicators associated with sensorineural hearing loss, conductive hearing loss, or both to help identify neonates in need of early hearing screening. Indicators for determining which infants should be provided with rescreening or periodic monitoring of hearing were also developed. The following excerpt from the 1994 Statement provides a reprise of the indicators 41 : AFor use with neonates (birth–28 days) when universal screening is not available 1Family history of hereditary childhood sensorineural hearing loss 2In utero infection, such as cytomegalovirus (CMV), rubella, syphilis, herpes, and toxoplasmosis 3Craniofacial anomalies, including those with morphologic abnormalities of the pinna and ear canal 4Birth weight of less than 1500 g 5Hyperbilirubinemia at a serum level requiring exchange transfusion 6Ototoxic medications including, but not limited to, the aminoglycosides used in multiple courses or in combination with loop diuretics 7Bacterial meningitis 8Apgar scores of 0 to 4 at 1 minute or 0 to 6 at 5 minutes 9Mechanical ventilation lasting 5 days or longer 10Stigmata or other findings associated with a syndrome known to include a sensorineural hearing loss, a conductive hearing loss, or both BFor use with infants (29 days–2 years) when certain health conditions develop that require rescreening 1Parent or caregiver concern regarding hearing, speech, language, or developmental delay 2Bacterial meningitis and other infections associated with sensorineural hearing loss 3Head trauma associated with loss of consciousness or skull fracture 4Stigmata or other findings associated with a syndrome known to include a sensorineural hearing loss, conductive hearing loss, or both 5Ototoxic medications including, but not limited to, chemotherapeutic agents or aminoglycosides used in multiple courses or in combination with loop diuretics 6Recurrent or persistent otitis media with effusion for at least 3 months CFor use with infants (29 days–3 years) who require periodic monitoring of hearing. Some newborns and infants may pass initial hearing screening but require periodic monitoring of hearing to detect delayed onset sensorineural hearing loss, conductive hearing loss, or both. Infants with these indicators require hearing evaluation at least every 6 months until age 3 years and at appropriate intervals thereafter. Indicators associated with delayed onset sensorineural hearing loss include: 1Family history of hereditary childhood hearing loss 2In utero infection, such as CMV, rubella, syphilis, herpes, or toxoplasmosis 3Neurofibromatosis type II and neurodegenerative disorders4. Persistent pulmonary hypertension in the newborn period Indicators associated with conductive hearing loss include: 1Recurrent or persistent otitis media with effusion 2Anatomic deformities and other disorders that affect eustachian tube function 3Neurodegenerative disorders Proposals for additional universal newborn screening requirements are viewed with a healthy skepticism by neonatologists and others responsible for implementing screening programs. The level of test sensitivity and specificity must be considered carefully when proposing mass newborn screening for a low incidence disorder, such as hearing loss. Insufficient capacity for processing large numbers of initial screening failures expeditiously through a rescreening paradigm to eliminate false-positive results can cause a screening program to fail. An optimal protocol would permit infants with normal hearing to be accurately segregated from those with true-positive results who need expensive follow-up, as well as sparing neonates with transient conductive losses the necessity of follow-up.