Extremely low birth weight infants are at high risk for auditory neuropathy

Abstract

Auditory neuropathy (AN) is a condition in which transmission of sound to the brain is abnormal. This is reflected as an electrophysiologic profile of normal otoacoustic emissions (OAE), with abnormal auditory brainstem evoked responses (ABR). Functionally speech perception is impaired and management strategies remain controversial. AN can be missed if high-risk newborns are screened for hearing loss with only OAE testing. The rate of sensorineural hearing loss (SNHL) in high-risk nursery infants is 10 times greater compared with normal term newborns. Therefore, we hypothesize that infants from the neonatal intensive care unit (NICU) are at significantly higher risk for AN than normal term infants. The objective of this study is to establish a prevalence rate and characterize risk factors for NICU graduates who demonstrate the AN electrophysiologic profile. This retrospective study examined infants admitted to the NICU at Kapi'olani Medical Center for Women and Children in Honolulu, HI from 1999 through 2003. Infants were screened with automated ABR. Diagnostic testing and OAE were performed before discharge if the ABR was abnormal. Hospital courses of 24 AN, 71 SNHL and 95 gestational age (GA)-matched control infants with normal hearing were reviewed. With a SNHL prevalence of 16.7/1000, the rate for AN was 5.6/1000 NICU infants. Compared to infants with SNHL, infants with AN were significantly younger (GA 28.3+/-4.8 AN vs 32.9+/-5.2 weeks SNHL, P<0.0001) and smaller (BW 1318+/-894 AN vs 1968+/-1006 g SNHL). Nearly two-thirds of the AN infants were ELBW and had significantly longer hospital stays compared to SNHL infants of the same birth weight group. Exposure to furosemide, aminoglycosides, vancomycin or dexamethasone was associated with increased AN but not SNHL. Peak bilirubin level correlated with SNHL but not AN. Low birth weight NICU infants are at significant risk for AN. ELBW infants are at significantly higher risk for both AN and SNHL. Infants admitted to the NICU should be routinely screened by automated ABR and if abnormal, further evaluation should be started before hospital discharge. Early identification of AN will result in better understanding of this disorder and lead to the development of appropriate intervention strategies.