10Troubleshooting & special cases

Objective measures are useful at every fitting, but they are decisive in the hard cases — the ones where behaviour is ambiguous, the anatomy is unusual, or the device is misbehaving. This module pulls the toolbox together around the scenarios that make a programming audiologist reach for it: a dys-synchronous nerve, a malformed cochlea, a recipient who has quietly stopped doing well, a twitching face, a percept that is anything but sound.

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]

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.

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.

TCWorked cases