A cochlear implant — a complex electric device that partially restores hearing — is a viable option to manage hearing loss associated with Charcot-Marie-Tooth (CMT) disease, according to a case report.
The report, “Cochlear Implantation in Charcot-Marie-Tooth Disease: Case Report and Review of the Literature,” was published in the journal Case Reports in Medicine.
CMT affects the peripheral nervous system — the network of nerves that transmit motor and sensory messages back and forth between the central nervous system (brain and spinal cord) and the rest of the body.
About 5% of patients with CMT exhibit sensorineural hearing loss (SNHL) or “nerve deafness,” which has been associated with mutations in the genes for peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ), or connexin-32 (GJB1).
CMT-associated hearing loss is thought to result from damage to the cochlear nerves — the nerve pathways that connect the inner ear sound detection system to the area of the brain that interprets sounds.
Patients may be able to hear sounds, but have trouble recognizing spoken words, and often report difficulty understanding others when there is a lot of loud background noise, at a party or a concert, for example.
Hearing loss and impaired speech perception can significantly impact patients’ quality of life and negatively affect communication, socialization, and learning development of children with CMT, especially if left undiagnosed for a long period of time.
Hearing aids, small electronic devices placed in or behind the ear that amplify sound, can help patients with hearing loss. However, when patients no longer benefit from hearing aids or experience severe hearing loss, surgery to place a cochlear implant — which converts the sound to electric pulses that are transmitted to the inner ear — may be a more effective option.
In CMT-associated hearing loss, cochlear nerve damage is thought to prevent meaningful auditory stimulation through an implant, but two success cases have been previously reported.
One case described a 67-year-old man, and the second a 53-year-old woman with CMT-associated hearing loss. Both cases demonstrated significant improvements in speech discrimination scores — the man at nine months and the woman at six months post-surgery — with a slower progression than the typical subset of patients who receive cochlear implants.
Now researchers at the Mayo Clinic in Rochester, Minnesota, have reported a third case of a cochlear implant that successfully improved hearing and speech perception in a patient with CMT-associated hearing loss.
The patient, a 70-year-old man with CMT, reported deafness in his left ear for the past 15 years. He initially wore hearing aids in both ears, but eventually stopped using the left one because of progressive hearing decline that wasn’t helped by the hearing aid.
Clinical testing revealed a profound hearing loss in the left ear, and moderate to severe hearing loss in the right ear. Surgery to place a cochlear implant was performed in his left ear.
Upon activation of the cochlear implant three weeks after surgery, the patient reported excellent access to sound, and showed gradual hearing improvement at each subsequent visit. Seven months after the surgery, speech perception had significantly improved, from 0% pre-implant to 32% on the AzBio sentence lists test and 53% on the CNC phoneme test.
“While no definitive recommendations concerning the efficacy of CI [cochlear implantation] in patients with CMT have been established, our results corroborate two earlier reports that cochlear implantation is a viable option for rehabilitation of SNHL in CMT patients,” the researchers wrote.
They noted that future studies are required to clarify the role of cochlear implants in CMT-associated hearing loss.