gms | German Medical Science

Objective: To present a candidacy concern regarding possible benefit from cochlear implantation, and to report intra- and post- implantation EABR and ECAP recordings in two profoundly hearing impaired patients with a known progressively deteriorating neurological condition and potentially significant peripheral and central nerve system (CNS) degeneration. Patients: First patient, a 25-year-old woman with Mitochondrial Neuro-Gastro-Intestinal Encephalopathy (MNGIE) presented with sudden profound bilateral sensorineural hearing loss with no benefit from conventional hearing aids. Second patient, a 5-year-old girl with Mitochondrial Metabolic Disease with severe complex I deficiency. She presented with progressive profound hearing loss two years prior to cochlear implantation. Normal hearing was reported in early childhood.

In both patients Auditory Brainstem evoked Response (ABR) recording was performed prior to implantation, and electrical compound auditory evoked potential (ECAP), using the Neural Response Telemetry (NRT) Nucleus CI24 software, was recorded intra-operatively and over time post-operatively. Additionally, Electrical Auditory Brainstem evoked Response (EABR) was recorded 29 months post implantation in the first patient and 9 months post implantation in the second patient.

Pre-implantation recording: both patients had no response in ABR. Those results were compatible with the severe to profound hearing loss, and could not be clearly related to the neurological problems.

Intra-operative and post operative recordings:

First patient (adult, MNGIE, length of follow-up 29 months): intra-operative NRT recordings were normal for amplitude growth function (AGF) and NRT thresholds. Two months post-implantation NRT recordings of refractory recovery function (RRF) measured across electrodes revealed fast recovery time (2000 microseconds). The patient however preferred a relatively slow rate of stimulation (900Hz, ACE map). Twenty-nine months after implantation NRT recordings showed elevated threshold levels with poor wave morphology. There were no clear RRF recordings and absent EABR recordings across all electrodes. At that time no significant changes were seen in her map. Speech perception performance 29 months post implantation: 100% open set CID identification and consistent and fluent telephone use.

Second patient (5 years old child, complex I deficiency, length of follow-up 9 months): intra-operative NRT recordings were normal for AGF and NRT thresholds. Nine months post-implantation NRT recordings showed normal AGF and normal NRT thresholds. EABR could be recorded across electrodes, with prolonged III-V inter peak latencies, and prolonged waves III and V absolute latencies. Nine-month post-CI speech perception performance: identifies words in closed set and understands familiar simple every day sentences. At this point she has achieved a reasonable expected outcome for duration of device use.

In these two patients with known CNS degeneration the poor objective test results which considered to represent poor neural synchronization of auditory tract at brains stem level, do not correlate with the consistent and good actual performance. Both of them probably have sufficient auditory neural synchronization which allows them to benefit from electrical stimulation. However we do not know yet if these results have any predictive value for further neural degeneration.