Transient infantile auditory neuropathy and its clinical implications.

OBJECTIVE

Auditory neuropathy (AN) has been a well-accepted clinical entity during the last years. Though we are able to diagnose AN reliably, little is known concerning its epidemiology, etiology and prognosis. This study is aimed at presenting a particular characteristic of the disease, namely its potential transient behaviour, observed in a group of high risk neonates suffering from AN. The ensuing clinical implications are underlined.

METHOD

From 1995 to 2004, 1150 high risk (HR) neonates were subjected consecutively to audiological evaluation by auditory brain stem responses (ABR), participating in a targeted hearing screening program for HR neonates. All neonates with ABR threshold >40 dBnHL and middle ear free from disease underwent otoacoustic emissions (OAEs) testing as well. Children with elevated ABR thresholds were scheduled for re-examination after 4-6 months. Only infants demonstrating considerably elevated thresholds (>70 dBnHL), absent or atypical ABR in combination with normal OAEs were considered as suffering from AN.

RESULTS

One hundred and seventy-seven neonates showed elevated ABR thresholds (15.4%). Seventy-nine of them demonstrated ABR thresholds >or=75 dBnHL, absent or strongly atypical waveforms at maximum test intensity and among them 25 displayed findings consistent with AN. Follow-up examination revealed a resolution of AN in 13 out of 20 infants retested, that is a restoration of ABR to normal and typical OAEs recordings. Using multiple logistic regression, we found that low birth weight may represent a reliable predictor for clinical recovery of AN infants.

CONCLUSION

This article bring to light the temporary character that AN could show in HR neonates and especially in those with low birth weight. Based on the results of our study, the higher the birth weight, the less likely it is for neonates to recover from AN. From a practical point of view, these findings suggest that hearing screening protocols for HR neonates should be revised in both their methodology and time of application. Finally, the decision for amplification or cochlear implantation in HR infants with AN should be made very carefully and well after the 6th month of age, since the maturation process may still be in progress.