Longitudinal Acoustic Threshold and Concurrent Electrode Impedance Changes After Cochlear Implantation With Lateral...

To investigate changes in hearing sensitivity post cochlear implantation with MED-EL and Advanced Bionics (AB) lateral wall electrode arrays, with a focus on characterizing delayed onset hearing loss (doHL) and concurrent electrode impedance changes.

A retrospective review of 96 adult cochlear implant (CI) recipients (101 ears; MED-EL: 51, AB: 50). Hearing sensitivity was assessed using the low-frequency pure tone average (LFPTA; 125, 250, 500 Hz). Immediate decrements in hearing sensitivity were considered separately from delayed decrements. The incidence, degree, and timing of doHL were characterized. Electrode impedances were considered for individuals with doHL compared with those with stable hearing.

Median immediate hearing loss was 19 dB across manufacturers. At initial activation, 73% of subjects had functional (LFPTA <80 dB HL) hearing. When all subjects with variable postoperative time periods were included, the incidence of doHL was 27% with a median degree of 24 dB. The median time doHL occurred was 76 weeks. Most (79%) subjects were categorized with gradual decrements rather than precipitous. No MED-EL subjects with doHL experienced concurrent impedance changes; 3 AB subjects did. Incidence of doHL rose to 31% and 44% when considering the subset of subjects with at least 1 year and 2 years of postoperative follow-up, respectively.

DoHL that was precipitous in nature was observed less frequently than previously reported. Although precipitous hearing loss tended to occur shortly after surgery, most instances of doHL occurred later than anticipated. The absence of concurrent impedance changes for recipients of MED-EL electrode arrays is consistent with previous reports.