Responsiveness of the Electrically Stimulated Cochlear Nerve in Children With Cochlear Nerve Deficiency.
Shuman He, Bahar S Shahsavarani, Tyler C McFayden and 7 others
PMID 28678078WHAT IT FOUND
In children with cochlear nerve deficiency, implant-evoked nerve responses were often absent, especially toward the cochlea's apex, and were weaker than in children with normal nerves.
This may guide expectations about variability in implant outcomes, but speech outcomes were not tested.
Key findings
01Measurable implant-evoked nerve responses varied widely in children with cochlear nerve deficiency: four children had none, seven had responses at all tested electrodes, and the percentage of electrodes with measurable responses fell from 79% to 20% as stimulation moved from base to apex.
02Compared with children with normal-size nerves, children with cochlear nerve deficiency had flatter response-growth slopes (mean 0.72/nC vs 0.88/nC), higher thresholds (mean 24.61 nC vs 8.40 nC), smaller maximum responses (mean 109.51 μV vs 241.70 μV), and longer t0 refractory time constants (mean 1.31 ms vs 0.62 ms).
03The tau refractory recovery time constant did not differ between groups (mean 1.13 ms in children with cochlear nerve deficiency and 1.16 ms in children with normal-size nerves).
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
Read the rest of this summary
You get three full summaries a month, free, and we do not ask for a card. Search, the TL;DRs and your library stay unlimited either way.
What it does not show
The study did not measure speech perception or language, so it cannot show whether these nerve-response differences predict communication outcomes. Only 18 children with cochlear nerve deficiency were analysed after four had no measurable responses and one was excluded as an outlier, so individual prediction is limited. Testing settings were not identical: children with cochlear nerve deficiency often needed longer pulse durations, lower probe rates, lower amplifier gain, and more averaged sweeps, and some had only a few testable electrodes. Nerve size was judged from MRI reconstructed images, which can have spatial-resolution and positioning errors. The maximum response used to model the input-output function was estimated from controls rather than measured directly, which may affect slope estimates. The study did not show how these measures should be used clinically to choose programming parameters or predict implant benefit. All children were already implanted with at least six months of listening experience, so findings do not address pre-implant decisions.
Declared interests
No conflicts of interest were declared.
The easy way to misread this
Do not read these nerve-response measures as a clinical test that predicts a child's speech or language outcome. The study did not assess speech perception or language, and it says no clinical tool for predicting cochlear implant outcomes exists.