Indian Journal of Otology

ORIGINAL ARTICLE
Year
: 2018  |  Volume : 24  |  Issue : 4  |  Page : 219--222

Auditory & verbal outcomes following cochlear implant in patients with demyelinating diseases of brain


Ankur Barot1, Rajesh Vishwakarma1, Nisarg Mehta1, Kalpesh Patel1, Dipesh Darji1, Chandrakant Vishwakarma2,  
1 Department of ENT and Head-Neck Surgery, Civil Hospital, Ahmedabad, Gujarat, India
2 Shabda Brahma Speech and Hearing Clinic, Ahmedabad, Gujarat, India

Correspondence Address:
Dr. Ankur Barot
Department of ENT and Head-Neck Surgery, Civil Hospital, Ahmedabad - 380 006, Gujarat
India

Abstract

Objective: The objective of the study was to evaluate early auditory and verbal outcomes following cochlear implant (CI) in patients with radiological findings suggestive of demyelinating lesions in the brain. Methods: The study was conducted in the Department of ENT, Civil Hospital, Ahmedabad, Gujarat. We studied and evaluated early auditory and verbal outcome following CI in 30 patients who had demyelinating lesions in the brain on magnetic resonance imaging, of 1- to 5-year age group. Hearing and speech ability was recorded on categories of auditory performance (CAP) scale and speech intelligibility rating scale and was compared to patients with normal cerebral myelination. Results: Patients in case group showed comparable scores on CAP scale and speech intelligibility scale compared to the patients who did not have demyelinating disease in the same time frame. Conclusion: Patients with demyelinating lesions showed similar auditory and verbal responses compared to normal implant patients who show that demyelinating diseases do not pose limitations in the early outcome of auditory response in such patients.



How to cite this article:
Barot A, Vishwakarma R, Mehta N, Patel K, Darji D, Vishwakarma C. Auditory & verbal outcomes following cochlear implant in patients with demyelinating diseases of brain.Indian J Otol 2018;24:219-222


How to cite this URL:
Barot A, Vishwakarma R, Mehta N, Patel K, Darji D, Vishwakarma C. Auditory & verbal outcomes following cochlear implant in patients with demyelinating diseases of brain. Indian J Otol [serial online] 2018 [cited 2019 Jun 27 ];24:219-222
Available from: http://www.indianjotol.org/text.asp?2018/24/4/219/254225


Full Text



 Introduction



A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged. This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency in sensation, movement, cognition, or other functions depending on which nerves are involved. Demyelinating diseases of the central nervous system can be classified according to their pathogenesis into several categories: demyelination due to inflammatory processes, viral demyelination, demyelination caused by acquired metabolic derangements, hypoxic–ischemic forms of demyelination, and demyelination caused by focal compression.[1] Some of these distinctions are rather simplistic in that there is overlap in pathogenesis between the entities in the different categories, but the classification provides a conceptual framework that may be useful in accurate diagnosis. Common sites for demyelination in brain include frontoparietal, periventricular, and temporal regions [Figure 1]. There are broadly divided into two types of demyelinating diseases:{Figure 1}

Demyelinating myelinoclastic diseaseDemyelinating leukodystrophy disease.

Causes of demyelinating diseases include genetics, infections, viral, chemical toxins, and autoimmune reactions.

A cochlear implant (CI) is a surgically implanted electronic device that provides a sense of sound to a person who has severe-to-profound sensorineural deafness. CIs bypass the normal hearing process; they have a microphone and some electronics that reside outside the skin, generally behind the ear, which transmits a signal to an array of electrodes placed in the cochlea, which stimulate the cochlear nerve.

The primary auditory cortex lies in the superior temporal gyrus of the temporal lobe and extends into the lateral sulcus and the transverse temporal gyri (also called Heschl's gyri). Final sound processing is then performed by the parietal and frontal lobes of the human cerebral cortex. Broca's area is a region in the frontal lobe of the dominant hemisphere (usually the left) of the hominid brain with functions linked to speech production. Thus, speech processing areas and auditory areas are situated in fronto-parieto-temporal lobes of the brain. Because of the fact that demyelination of the neurons results in dyssynchrony, role of CI was debatable when the demyelination is affecting the brain because of questionable auditory and verbal outcome due to demyelination.[2]

Objective

The objective of the study was to evaluate the auditory and verbal outcome in patients having demyelinating lesions of brain, following cochlear implantation, and compare the results with auditory–verbal outcome of the patients with normal cerebral myelination.

 Methods



This was a retrospective study carried out over a period of 3 years, from July 2012 to June 2015 at Apex tertiary care institute. Written and informed consent was taken from the guardians of all the children. Approval of ethical committee was taken before commencing the study.

In this study, Group A comprised 30 patients who had demyelinating lesions in brain on magnetic resonance imaging (MRI) scan. Patients in the Group A were of age from 1 to 5 years, were congenitally deaf and mute, and had severe-to-profound sensory neural hearing loss on audiological tests. The hearing assessments of these children included appropriate behavioral audiometric techniques, objective measures of middle-ear function, acoustic reflex studies, transient otoacoustic emissions or distortion product (DPOAE), auditory brainstem responses (ABRs), and auditory steady-state response. Group B comprised 30 patients who were of age from 1 to 5 years, were congenitally deaf and mute, had severe-to-profound sensory neural hearing loss on audiological tests, and not having any other associated medical illness. These patients had normal MRI brain with normal myelination. None of the patients in control group had delayed development.

Etiology of demyelination in Group A was as follows [Figure 2]:{Figure 2}

Etiology of deafness in patients of Group A [Figure 3]Etiology of deafness in patients of Group B [Figure 4]{Figure 3}{Figure 4}

Of the 30 patients, 12% patients had frontal lobe demyelination, 20% patients had temporal lobe demyelination, 18% had parietal lobe demyelination, 25% had temporo-parietal demyelinating foci, 15% had fronto-parieto-temporal lobe demyelination, and 10% had occipital lobe demyelination. Out of 30 patients in Group A, two patients had delayed development.

Preoperatively, these children received complete medical examinations at Civil Hospital, Ahmedabad, including related consultations in audiology, pediatrics, neurology, medical genetics, otolaryngology, psychology, speech pathology, and radiology.

All the 60 patients underwent CI surgery. After placement of the internal CI devices, intraoperatively, we measured electrode impedances, visually detected electrical stapedius reflexes, and auditory response telemetry or neural response telemetry (NRT). These intraoperative objective measures were used to help program the speech processor for each child. Postoperatively, each child has had regular follow-up to assure complete healing of the surgical incision, to assess their general medical conditions, and for speech processor programming. Their hearing and communication skills have been assessed on a regular basis on categories of auditory performance (CAP) score and speech intelligibility rating (SIR) score; postoperatively, we have also repeated electrode impedance measurements, NRT measurements, otoacoustic emissions, and electrical ABRs (EABRs). We now have follow-up information of the children ranging from 6 months to 2 years. This assessment was done after 6 months, 12 months, 18 months, and 24 months after surgery.

 Results



The 60 children implanted at Civil Hospital, Ahmedabad, have not had any postoperative medical or CI device complications. All of the children have shown significant improvements in their sound detection, speech perception abilities, and communication skills. All of the children have shown evidence of good NRT results. All showed evidence of good postoperative EABR results. Auditory and verbal responses were assessed and scored on CAP and SIR scale at the intervals of 6 months, 12 months, 18 months, and 24 months.

As per [Figure 5] Average SIR score in Group A at 6, 12, 18, and 24 months was 1, 1, 2, and 3, respectively, while in Group B, it was 1, 2, 2, and 3. As per [Figure 6] Average CAP score in Group A at 6, 12, 18, and 24 months was 1, 3, 3.5, and 4, respectively, while in Group B, it was 2, 3, 4, and 5.{Figure 5}{Figure 6}

The results of CAP and SIR scores in the patients with demyelinating diseases of brain at the interval of 6, 12, 18, 24 months were comparable with the patients with normal demyelination of the brain.

For SIR score, t-test was applied using IBM social science system version SPSS 17.0 (SPSS Statistics for Windows, Version 17.0. Chicago: SPSS Inc.) software (t = −0.24254 and P = 0.408222). The result is not statistically significant at P < 0.05. Hence, it can be concluded that there is no significant difference in SIR scores of patients with demyelinating lesions in brain and without demyelinating lesions in brain.

For CAP score, t-test was applied using SPSS (Statistical Package for the Social Sciences) software (t = −0.67832 and P = 0.261426). The result is not statistically significant at P < 0.05. Hence, it can be concluded that there is no significant difference in SIR scores of patients with demyelinating lesions in brain and without demyelinating lesions in brain.

Average CAP and SIR scores according to area involved in demyelination are discussed in [Figure 7] and [Figure 8].{Figure 7}{Figure 8}

 Discussion



Myelination of neuron provides protection of neurons and helps in rapid conduction of electrical stimuli across the axon. Outer hair cells act as transducer which converts mechanical energy into electrical stimulus which in turn carried to the brain through 8th nerve to auditory and speech areas of the brain. In a patient with CI, the electrodes directly stimulate the 8th nerve, bypassing the normal acoustic sound conduction. There were logical bases for assuming that a CI would not be an appropriate or especially successful intervention for what researchers thought was that because of demyelinating disease there would be delayed and desynchronous stimulation.[3]

It has been shown that if a nerve fiber is stimulated electrically, both the growth of discharge rate and the maximum rate achievable are greater than when stimulating the nerve acoustically. In addition, the timing of the nerve response to electrical stimulation seems to be more precise and repeatable than it is for acoustic stimulation.[4] Period histograms of neural responses show that spikes in the action potential occur more often around the phase peak when using electrical stimulation than when using acoustic stimulation, for which the spikes are more spread out along the entire phase curve (Abbas, 1993).[5] The suggestion has also been offered that the discrete biphasic pulses used in most CI stimulation strategies may assist in increased synchrony of the firing pattern of the auditory nerve (Rance, 2005).

Finally, the fact should not be overlooked that there can also be deterioration of the auditory neurons in patients with deafness due to sensorineural hearing loss, and these are the types of patients for whom CIs were specifically developed and who typically benefit significantly from the device (Spoendlin and Schrott, 1989). Thus, electrical stimulation can be more effective at producing a synchronous neural response than acoustic stimulation.[6]

In this study, the auditory–verbal outcome in the patients with demyelinating disease is comparable with patients with normal myelination. This suggests that stimulating the nerve electrically in patients with demyelinating diseases provides comparable results when compared to patients with normal demyelination.

 Conclusion



Our experiences with cochlear implantation for children diagnosed with demyelinating diseases of brain have been positive. The 30 children we have implanted have not had any complications postoperatively, and each child has shown improved listening and communication skills that have enabled each child to take advantage of different communication and educational options. Although sample size in this study was small, randomized control trials including a large number of patients should be done to establish statistical significance.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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