Amplified Ears and Listening Brains

Amplified Ears and Listening Brains: The Role of Cochlear Implantation in Severe to Profound Sensorineural Deafness

Sheelu Srinivas*

Consultant ENT and Cochlear Implant Surgeon, Kauvery Hospital, Electronic City, Bengaluru, India

Sensorineural Hearing Loss in Children and Adults

Hearing loss may be caused by interference with the transmission of sound from the outer to the inner ear (conductive hearing loss) or damage within the cochlea, the auditory nerve, or auditory centres in the brain (sensorineural hearing loss).

Severe to profound hearing loss in children may have a genetic aetiology, or have prenatal, perinatal, or postnatal causes. These include conditions such as meningitis and viral infection of the inner ear (for example, rubella or measles), as well as premature birth and congenital infections.

In adults the most common cause of sensorineural hearing loss is presbycusis. This is a progressive condition caused by the loss of function of hair cells in the inner ear, leading to deafness. Hearing loss in adults may also be caused by excessive exposure to noise, or by ototoxic drugs, metabolic disorders, infections, or genetic factors.

Deafness that occurs before the development of language is described as prelingual, whereas deafness that occurs after the development of language is described as post lingual.

Deaf and Dumb is obsolete. 95% of deaf persons have normal IQ. They are not able to perform as deafness is a sensory disability which is directly related to cognition. There are various studies showing cognitive decline in elderly deaf who do not wear hearing aids at the right time.

Need of CI and Practice guidelines

Services for people who are deaf aim to improve their quality of life by maximising their ability to communicate, using the means most appropriate for the person and their environment, and to enable the person to move safely within their environment.

Early diagnosis is crucial for deafness habilitation. We call it 0-3-6 rule.

Screening at birth, confirmation of deafness by 3 months and fitting of hearing aids within 6 months.

Most of the countries in the world have mandatory Newborn hearing screening at birth. In India, NHS has been made mandatory only in few states. In private sector, many hospitals are offering hearing screening at birth.

BERA Test in an infant

If baby fails 2 screening tests- then ABR/BERA is performed. Once hearing loss is confirmed, hearing aids are fitted within 6 months of birth and aggressive auditory verbal therapy is started.

While sign language is still a modality of choice for communication, it has been difficult in our country. Oral speech and communication are preferred as most pf the deaf children are born to normal hearing parents and it also helps to mainstream educate them.

This child fitted with hearing aids is assessed for improvement in speech and language skills. If the child is not achieving age-appropriate skills, they are referred for cochlear implant candidacy work up. Potential candidates receive a multidisciplinary assessment to determine whether cochlear implantation is suitable. Both audiological hearing and functional hearing are assessed as part of the multidisciplinary assessment, as well as other factors such as fitness for surgery, structure of the cochlea, the presence of a functioning auditory nerve and the likely ability of the person to derive benefit from the stimuli produced by the cochlear implant system.

For a post lingual deaf candidate or an adult deaf -it is advised to work up for CI candidacy and fit with hearing aids to look for auditory benefit.

The CI Technology

Cochlear implant systems consist of internal and external components. A microphone and sound processor are worn externally behind the ear. The sound processor is connected to a transmitter coil, which is worn on the side of the head. Data from the transmitter coil are passed to a receiver-stimulator package that is implanted into a surgically fashioned depression in the mastoid bone. The receiver-stimulator translates the data into electrical pulses that are delivered to an array of electrodes.

Fig.1. On table C arm X-ray of internal package in situ

These are placed surgically within the cochlea. The electrodes stimulate spiral ganglion cells that innervate fibers of the auditory nerve. The activation of electrodes provides a sensation of hearing but does not restore hearing.

The surgery is followed by switching on of the device and auditory verbal therapy

Fig. 2. Child wearing the external processor

Quality of life and education outcomes

The studies of educational outcomes suggest that children who are profoundly deaf and have a cochlear implant may be more likely to be educated within a mainstream school than children with a similar level of deafness but without a cochlear implant. The studies also suggest that children who are profoundly deaf and have a cochlear implant may have a higher level of academic performance than those who are profoundly deaf but have no cochlear implant.

The outcome of a CI depends on multiple factors including age of implantation, therapy duration, mapping, social factors and education of family to name a few.

Cost-effectiveness

Cochlear Implants are expensive and need lifetime maintenance. Presently, a basic CI system with surgery can cost a minimum of 8 lakhs to 20 lakhs. This depends on the CI system chosen and therapy costs. When the lifetime dependency of a deaf person and loss of meaningful work due to profound deafness is considered- the investment in CI has been found cost effective. There are various studies since the technology was made commercially available about 4 decades ago.

Acknowledgment

NICE guidelines. Multidisciplinary team, Patients, and Parents

Dr. Sheelu Srinivas

Consultant ENT and Cochlear Implant Surgeon

Amplified Ears and Listening Brains