Clinical role of electrocochleography in children with auditory neuropathy spectrum disorder

Abstract

Objectives: To assess electrocochleography (ECochG) to tones as an instrument to account for CI speech perception outcomes in children with auditory neuropathy spectrum disorder (ANSD).

Materials & methods: Children (<18 years) receiving CIs for ANSD (n = 30) and non-ANSD (n = 74) etiologies of hearing loss were evaluated with ECochG using tone bursts (0.25-4 kHz). The total response (TR) is the sum of spectral peaks of responses across frequencies. The compound action potential (CAP) and the auditory nerve neurophonic (ANN) in ECochG waveforms were used to estimate nerve activity and calculate nerve score. Performance on open-set monosyllabic word tests was the outcome measure. Standard statistical methods were applied.

Results: On average, TR was larger in ANSD than in non-ANSD subjects. Most ANSD (73.3%) and non-ANSD (87.8%) subjects achieved open-set speech perception; TR accounted for 33% and 20% of variability in the outcomes, respectively. In the ANSD group, the PTA accounted for 69.3% of the variability, but there was no relationship with outcomes in the non-ANSD group. In both populations, nerve score was sensitive in identifying subjects at risk for not acquiring open-set speech perception, while the CAP and the ANN were more specific.

Conclusion: In both subject groups, the TRs correlated with outcomes but these measures were notably larger in the ANSD group. There was also strong correlation between PTA and speech perception outcome in ANSD group. In both subject populations, weaker evidence of neural activity was related to failure to achieve open-set speech perception.

Keywords: Auditory nerve neurophonic; Auditory neuropathy spectrum disorder; Cochlear implants; Compound action potential; Electrocochleography.

Figure 1

ECochG waveform and energy spectra characteristics of CI subjects. All stimuli were presented at 90 dB nHL. A. ECochG response and to 500 Hz and the corresponding FFT spectrum. Red portion of the waveform at the onset of the response indicates a CAP. Blue portion within the blue background indicates the ongoing, or steady-state portion of the ECochG response containing the CM and ANN. The red circles in the spectrum indicate the level required for the peaks to be significant (see Methods). B. ECochG recordings with increasing evidence of neural activity in the form of CAP and ANN. From top to bottom panel the visually apparent magnitudes of CAP and ANN increase resulting in a higher scores noted on the left of the panels. (Left) The ANN was determined using the ‘average cycle’ to low frequency tones. The average cycle is the average of all cycles in the ongoing portion of the response, as in the blue box in A. The responses shown are to different cases, and were to 500 (top two and bottom tracing), 750 (third from top), and 250 Hz (fourth and fifth from top). The degree that the average cycle deviated from the best-fit sinusoid (red dashed line) was used to determine the score for the ANN. (Right) The CAP was most apparent in the sum of the responses to alternating phase stimuli (blue lines). The score for the CAP is given at the left. The top and the bottom two panels are responses to 2000 Hz tone bursts, and the third and fourth panels are the responses to 500 Hz tone bursts.

Figure 2

Regression analysis of TR and speech perception outcomes in ANSD (A) and non-ANSD (B) pediatric CI recipients. Circle markers-subjects included in regression analysis. Triangle markers-subjects excluded from regression analysis based on Cook’s distance. Asterisk markers-subjects unable to complete speech perception testing.

Figure 3

Regression analysis of PTA and speech perception outcomes in ANSD (A) and non-ANSD (B) pediatric CI recipients Circle markers-subjects included in regression analysis. Triangle markers-data points excluded from regression analysis based on Cook’s distance. There were no outliers in non-ANSD group based on Cook’s distance analysis of PTA and PB-k, the triangles denote the outliers based on the TR and PB-k analysis included here to provide context. Asterisk markers-subjects unable to complete speech perception testing.

Figure 4

Proportion of ANSD CI recipients who achieve testable speech perception (white) and those who did not (grey) depending on their CAP, ANN and the Nerve score. CAP (A) and ANN (B) Scores of at least 1 and Nerve score (C) of at least 3.