10Troubleshooting & special cases

The recurring skill in this module is matching the measure to the question. Pick a scenario below to see which objective measures are primary, adjunct, or minor for it — then read the worked sections that follow.

TCAuditory neuropathy (ANSD)

In auditory neuropathy spectrum disorder, outer hair cells work but auditory nerve transmission is dys-synchronous — acoustic ABR is absent or grossly abnormal despite present otoacoustic emissions and cochlear microphonic. The CI question is whether electrical stimulation can produce the synchrony the acoustic pathway cannot. The eABR and ECAP are central: a present, replicable eABR supports that the nerve can carry a synchronous electrical signal centrally, predicting benefit and supporting candidacy.[2004]

The prognostic value here is largely binary — present versus absent, not graded. In ANSD children, those with a present ECAP after implantation go on to develop open-set speech, while those with an absent or grossly abnormal ECAP generally do not; a robust pre-implant transtympanic eABR likewise points to an outcome at least as good as for a cochlear (sensory) loss, whereas an absent one warns of limited benefit. The measure answers “can this nerve carry a usable electrical signal?” — it does not finely predict how well.[2010, 2007]

CMalformations & cochlear nerve deficiency

In cochlear malformations and cochlear nerve deficiency (a thin or absent nerve on MRI), objective measures convert an anatomical uncertainty into a functional answer. As developed in Module 6, a present eABR shows the nerve conducts despite looking thin, supporting a cochlear implant over an auditory brainstem implant; an absent eABR with a CI in place supports the ABI route. Malformed cochleae also raise the stakes on impedance and transimpedance findings, which help confirm electrode position when the anatomy is abnormal. (Note that cochlear nerve deficiency is an MRI diagnosis — CT cannot see the nerve — so imaging and the objective battery work together here.)

The degree of deficiency tracks the outcome, and the numbers are worth carrying: across series, roughly half of children with cochlear nerve deficiency go on to use spoken language, but the split by severity is wide — about 89% of nerve-hypoplasia ears versus ~47% of nerve-aplasia ears in one cohort, and a review found roughly 65% vs 30%developing useful speech discrimination on the same divide. A present eABR and ECAP push the prognosis toward the better end. So even an “absent” nerve on MRI is not an automatic veto — some aplasia ears still derive meaningful benefit, presumably via fibres travelling with other nerves in the internal auditory canal.[2016, 2017, 2020]

TCDevice failure workup — hard and soft

When a recipient deteriorates, the first fork is device versus biology, and objective measures triage it:

• Hard failure — an overt device fault, usually caught by integrity testing and grossly abnormal impedances. The device is non-functional and explant/re-implant follows.
• Soft failure — declining performance or aberrant percepts despite passing standard integrity checks. The 2005 consensus statement formalises the definition. Here objective measures matter most: impedance trends, integrity tests, ECAP changes, and exclusion of programming and middle-ear causes build the case for a soft failure when no single test is diagnostic.

[2005]

TCFacial nerve stimulation

Facial nerve stimulation — facial twitching driven by current spreading from the cochlea to the facial nerve — is suspected from patient report and can be characterised objectively. It is commoner with otosclerosis, malformations, and certain electrode positions. Management is guided by the objective picture: identify the offending electrode(s), then deactivate them, reduce their current, widen pulse width, or change stimulation mode to narrow current spread. Impedance and current-spread information help localise the culprit.

CNon-auditory percepts

Recipients sometimes report sensations that are not sound — facial or bodily tingling, dizziness, or discomfort on particular electrodes. These flag current escaping its intended target. The objective battery helps separate causes: impedance and TIM for electrode position and shorts, ECAP for whether auditory neurons are even being reached, and careful per-electrode mapping to isolate and deactivate the offenders. The principle throughout is that an aberrant percept is a localisation problem, and the objective measures are localisation tools.

CDo objective measures predict outcome?

It is tempting to expect the objective battery to forecast how well a recipient will hear. Mostly it does not — and being honest about that is part of using it well. Three threads from the outcomes literature:

• Electrode position does matter, and objective/imaging measures detect it. A perimodiolar array sitting fully in scala tympani is associated with better word recognition, whereas translocation into scala vestibuli and over-deep insertion predict poorer scores. Spread-of-excitation and the transimpedance matrix flag position electrophysiologically; CT confirms it.[2013, 2016]
• ECAP/eABR are present-or-absent prognostic flags, not graded predictors. Their presence signals a nerve that can carry an electrical signal (decisive in ANSD and nerve deficiency); ECAP threshold, AGF slope, and recovery do not reliably scale with speech score in routine recipients.[2010, 2020]
• Some intuitive measures simply don't predict. Spiral-ganglion-cell counts in temporal-bone studies correlate poorly with performance — substantial open-set speech is seen with a small fraction of normal neural elements — so a “healthier-looking” nerve is no guarantee, and a poor-looking one no veto.[2020]

The lesson mirrors the rest of the atlas: objective measures are strongest as localisation and integrity tools — is the contact intact, is the nerve responding, where is the array — and weakest as crystal balls for eventual speech understanding, which depends on central, cognitive, and rehabilitative factors the battery cannot see.[2020]

TCWorked case library

The fifteen cases below are interactive walk-throughs adapted from the case-study chapter of Wolfe & Schafer's programming text. Each puts you at the decision points a programming audiologist actually faces — choosing how to set or rescue levels, reading an impedance pattern, deciding device-versus-biology — and only advances when you pick the defensible option. Pick a number to begin; the real-world figures (current levels, NRT/eSRT offsets, impedance values) are the authors'.[2014, 2011]

TCWorked cases