The varieties of auditory neuropathy

Electrocochleography in auditory neuropathy

Auditory neuropathy (AN) is a disorder characterized by the absence or the severe impairment of the auditory brainstem responses (ABRs) together with the preservation of otoacoustic emissions and/or cochlear microphonic (CM). We recorded transtympanic electrocochleography (ECohG) evoked by 0.1 ms clicks in one young adult and in four children having distortion product otoacoustic emissions and absent ABRs. In all but one patient CM and summating potential (SP) were present with normal threshold, and their amplitudes appeared comparable to or higher than the values obtained from subjects with normal hearing. The compound action potential (CAP) was absent in two patients while in one subject CM and SP were followed by a highly desynchronized neural activity. A broad CAP was found in two children and the threshold appeared clearly elevated in one of them, while it showed only a mild elevation in the other. No correlation was found between CAP and behavioral thresholds. These results suggest that ECohG can be useful in AN diagnoses since it is the only reliable tool in evaluating the auditory peripheral function in the presence of a desynchronized ABR.

Speech perception and cortical event related potentials in children with auditory neuropathy

OBJECTIVES

1) To investigate the unaided and aided speech perception abilities of children with auditory neuropathy (AN) and to compare their performance to children with sensorineural hearing loss. 2) To establish whether cortical event related potentials (ERPs) could be recorded in children with AN, and to determine the relationship between the presence of these responses and speech perception.

DESIGN

Unaided and aided speech perception assessments (PBK words), and cortical-ERP testing was carried out in a group of 18 children with AN. Data also were obtained from a cohort of age and hearing level matched children with sensorineural hearing loss.

RESULTS

The speech perception performance of the 15 children with AN able to complete a PBK-word assessment, fell into two distinct categories. The children either showed no open-set speech perception ability (7/15 cases), or performance levels similar to their sensorineural counterparts (8/15 cases). Approximately 50% of children with AN showed ERPs of normal latency, amplitude and morphology. In all cases, response presence (at normal latencies) was consistent with reasonable speech perception ability, and response absence was consistent with negligible speech perception.

CONCLUSIONS

In approximately 50% of children with auditory neuropathy, the provision of amplification results in significant open-set speech perception improvements. The results confirm the previously published reports that speech perception ability cannot be reliably estimated from the behavioral audiogram in children with AN. Obligatory ERP test results may offer a means of predicting perceptual skills in newly diagnosed youngsters as the presence of ERPs (with age-appropriate latency and morphology) was correlated with significant open set speech perception abilities and amplification benefit. The absence of the ERP in contrast, indicated profound hearing disability evidenced by profound hearing loss and/or extremely poor speech perception.