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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 26  |  Issue : 3  |  Page : 164-168

Hearing threshold of deaf pupils in Kaduna metropolis, Kaduna, Nigeria: A cross-sectional survey


1 Department of Otorhinolaryngology, Abubakar Tafawa Balewa University Teaching Hospital, Bauchi, Nigeria
2 Department of Clinical Services, National Ear Care Centre, Kaduna, Nigeria
3 Department of Otorhinolaryngology, Aminu Kano Teaching Hospital, Kano, Nigeria
4 Department of Otorhinolaryngology, Federal Medical Center, Yola, Nigeria

Date of Web Publication13-Aug-2019

Correspondence Address:
Dr. Abdullahi Musa Kirfi
Department of Otorhinolaryngology, Abubakar Tafawa Balewa University Teaching Hospital, Bauchi
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/npmj.npmj_56_19

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  Abstract 

Background: Hearing loss in paediatric age group may be inherited, developmental or caused by maternal rubella. It may also be due to complications at birth or certain infections such as meningitis and measles. Ototoxicity and exposure to excessive noise also contribute significantly. Majority of hearing loss in children can be prevented primarily. We aimed to share our findings on assessing the hearing thresholds of pupils in deaf schools in Northwestern Nigeria. Participants and Methods: This was a cross-sectional study which assessed the hearing threshold of pupils in deaf schools in Kaduna metropolis, Kaduna, Nigeria. Approval was obtained from the State Ministry of Health Ethics Committee. Multi-staged sampling method was used to enrol 430 deaf pupils. Consent was obtained and a structured pre-tested questionnaire was used to generate data on the participant's biodata, history and detailed examination findings as well as pure-tone audiometry. Collated data were documented and entered into Statistical Product and Service Solutions version 20 for windows then analysed. Results: Mean pure-tone average of the right ear was 103.4 ± 8.3 and the left ear was 104.3 ± 8.9. Majority had bilateral profound hearing loss (99.0%). Severe hearing loss was seen in 0.9%, whereas the remaining 0.1% had moderate hearing loss. The hearing loss sensorineural in majority (97.6%) and the remaining 2.4% had mixed hearing loss. High-frequency hearing loss predominated (98.6%). Conclusion: Majority of the deaf pupils had bilateral, profound, sensorineural hearing loss, involving higher frequencies.

Keywords: Deaf pupils, hearing threshold, Kaduna


How to cite this article:
Kirfi AM, Samdi MT, Salisu AD, Fufore MB. Hearing threshold of deaf pupils in Kaduna metropolis, Kaduna, Nigeria: A cross-sectional survey. Niger Postgrad Med J 2019;26:164-8

How to cite this URL:
Kirfi AM, Samdi MT, Salisu AD, Fufore MB. Hearing threshold of deaf pupils in Kaduna metropolis, Kaduna, Nigeria: A cross-sectional survey. Niger Postgrad Med J [serial online] 2019 [cited 2019 Oct 18];26:164-8. Available from: http://www.npmj.org/text.asp?2019/26/3/164/264388


  Introduction Top


The ear is the organ of hearing. It is functionally divided into conductive parts consisting of the external ear, tympanic membrane, ossicles, auditory tube and labyrinthine fluids as well as perceiving apparatus which consist of the organ of Corti, auditory division of the vestibulocochlear nerve and central connections. Hearing loss can be conductive, due to defects in the external and middle ear, sensorineural, due to defects in the inner ear and its central connections, or mixed. The hearing loss in 50%–66% of children is mostly preventable.[1],[2],[3]

Hearing loss in the paediatric age group may be inherited, developmental or caused by maternal rubella. It may also be due to complications at birth or certain infections such as meningitis and measles. Ototoxicity and exposure to excessive noise also contribute to some extent. Majority of hearing losses can be primarily prevented.[4] Congenital ear malformations are known causes of deafness, about a third are associated with syndromes involving additional malformations or functional loss of organs.[5] Consanguinity, the advanced age of pregnant mothers, maternal exposure to toxins that affect the foetus and irradiation are some of the suspected risk factors associated with the development of such syndromes.[5] Defects affecting delamination of neural crest cells, their proliferation, apoptosis and/or migration or their reciprocal interactions with the three germ layers are possible explanations for the abnormality in growth of the hillocks responsible for the development of the ears in utero, repositioning and ultimately leading to congenital deafness.[5] Documented risk factors associated with congenital deafness include low birth weight, multiparity, acute illnesses among pregnant mothers and the use of unsafe medications in the first trimester of pregnancy.[6],[7],[8] Some other identified risk factors in the development of congenital hearing loss include chronic illnesses among pregnant mothers such as diabetes mellitus and uncontrolled hypertension. Multiple births, the advanced age of the pregnant mother, low educational status of the pregnant mother as well as low maternal socio-economic status were some of the factors identified.[6],[7],[8],[9] Luquetti et al.,[8] linked Hispanic ethnicity with high risk of development of congenital deafness.

Paediatric hearing loss is a major public health problem worldwide, especially in developing countries, Nigeria inclusive.[10] The degrees of the severity of deafness among children are graded as mild, moderate, severe and profound hearing losses.[3] Deafness affects only one ear or both ears. It could also be symmetrical or asymmetrical WHO[11] classification for hearing based on decibel of hearing level (dBHL) is ≤25 dB (normal hearing), 26 dB–30 dB (mild hearing loss), 31 dB–60 dB (moderate hearing loss), 61 dB–80 dB (severe hearing loss) and ≥80 dB (profound hearing loss).

There are very few studies conducted on deaf pupils in Africa including Nigeria and very few of those studies were conducted to assess their hearing with a view to re-categorizing them. The aim of this study was to determine the hearing thresholds of pupils in the deaf schools and to re-classify the pupils.


  Participants and Methods Top


This was a cross-sectional study that assessed the hearing threshold of pupils in deaf schools in Kaduna metropolis, Kaduna, Nigeria, between November 2016 and August 2017. Ethical approval was obtained from the Health Research Ethics Committee of the Kaduna State Ministry of Health residing within the ministry's premises; with protocol number MOH/ADM/744/Vol. 1/446 dated 8th September 2016. The sample size was calculated using the Fisher formula for cross-sectional study,

n = Z2pq/D2.

Where n = minimum sample size, z = normal standard deviate which is 1.96 (at 95% confidence interval), P = prevalence of hearing threshold among deaf pupils. No prevalence study was documented on hearing threshold of deaf pupils in Nigeria, the West African sub-region and Africa. Therefore, an estimated prevalence of 50% was used to calculate the sample size. Therefore: P = 0.5, q = 1 − p, q = 1 − 0.5 = 0.5, D = Degree of precision set at 5% = 0.05. Minimum sample size, n = 1.962 × 0.5 × 0.5/0.05 × 0.05. The calculated minimum sample size was 384.16, 10% of the total was added for attrition giving 422. Thus, the minimum sample size for the study was taken as 422. Four hundred and thirty pupils were enrolled using a multi-staged sampling method. Deaf pupils from the schools for the deaf in the metropolis were recruited for this study. Informed consent was obtained from pupils/parents. A structured pre-tested questionnaire was used to generate data on the participant's biodata, history and detailed examination findings as well as pure-tone audiometry. A TES 1350A model sound level meter (TES Electronics Taiwan) was used to measure the ambient noise level in the quietest room within the school. The sound level meter was placed at the level of the ear and measurements were taken at three different times, allowing the sound level meter to stay for 30 s before taking the measurements. An arithmetic mean of the three measurements was taken at each occasion. The mean ambient noise within the room was 33.3 dB.[12] A calibrated portable digital audiometer with the model (Graphic Digi IS Clinical Audiometer) was used to conduct pure-tone audiometry at frequencies of 250 Hz–8 KHz for air conduction (AC) and 500 Hz–4 KHz for bone conduction (BC).[13],[14]

The procedure was explained to the participants in sign language and their assent was obtained. The participants were seated on a chair in the test room wearing the headphone. Pure tones were delivered to each ear consecutively through the earphones to test for AC. BC was tested using bone vibrator. The participants responded by pressing a small hand-held button as soon as the tone was heard. Both ears were tested in the same fashion. The intensity of the pure tones was first presented just above the participant's suspected threshold then reduced at an interval of 10 dB stepwise until no sound is heard by the participant. The intensity was then increased at an interval of 5 dB stepwise until the participant responds. The procedure was repeated until the participant responds at a given intensity in two of three or three of five occasions. The frequencies were then varied from 1 KHZ to 8 KHZ, 500 HZ and 250 HZ. Accuracy of the subjects was then checked by testing the intensities at 1 KHZ, which was within 10 dB of the first result.

Conductive hearing loss was diagnosed when only the AC threshold was >25 dB. Sensorineural hearing loss was diagnosed when both AC and BC thresholds were >25 dB and the difference between the air and BC thresholds was <10 dB.[13],[14] Mixed hearing loss was diagnosed when both the air and BC thresholds were more than 25 dB and the difference between the air and BC thresholds was more than 10 dB.[13],[14] Pure-tone average (PTAV) expressed in dBHL was calculated for each ear at 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz to ascertain the hearing threshold and the degree of hearing disability for the respective ears. The pupils' hearing impairment classified according to the WHO (2014), no impairment (0–25 dB), mild hearing loss (26–30 dB), moderate hearing loss (31–60 dB), severe hearing loss (61–80 dB) and profound hearing loss >81 dB. Hearing impairment was considered to be serviceable when the degree of hearing impairment was severe or better, in the better hearing ear. Tympanometry was not conducted on the participants due to the unavailability of tympanometer to the authors at the time of the survey.

The generated data were coded and entered into Statistical Product and Service Solutions for Windows, version 20.0 (IBM, Chicago, Ilinois). Student's t-test and Chi-square test were used for statistical analysis and P value set at P < 0.05 as statistically significant.


  Results Top


The age range of participants was 6–17 years with a mean age of 13.48 ± 2.36. [Table 1] gives detail of the age and gender of participants. [Table 2] shows the detail of the findings on examination of the external auditory canals of the participants. In this study, 411 (95.6%) pupils had an intact tympanic membrane whereas 19 (4.4%) had perforated tympanic membranes. This was found to be statistically significant t (430) = −2.323, P = 0.02 ). Pupils with ear discharge had aural toileting done and serial ear dressing was done until dry ear was achieved. Those with ear wax had wax removal by either Jobson-Horne aural probe or ear syringing and then pure-tone audiometry was conducted 2 days after the ear syringing. Pupils with foreign bodies in their external auditory canal had the foreign body removed with Jobson-Horne aural probe.
Table 1: Age and gender distribution of the participants

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Table 2: External auditory canals finding of participants

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The degree and type of hearing loss among the participants are shown in [Table 3]. The range of PTAV among participants on the right ear was 65.0–120.0 dB with mean PTAV of 103.4 ± 8.3, whereas the range of PTAV on the left ear was 84.75–120.0 dB with mean PTAV of 104.3 ± 8.9. [Figure 1] shows a representative audiogram of one of the pupils. Most of the ears 839 (97.6%) had sensorineural hearing loss and the remaining 21 (2.4%) had mixed hearing loss. Majority of the ears 851 (99.0%) had profound hearing loss, 8 (0.9%) had severe hearing loss and the remaining 1 (0.1%) had moderate hearing loss. High-frequency hearing loss was the most commonly involved (98.6%). Nine ears among seven pupils with serviceable hearing losses had hearing aid fitted for them free by the Starkey Foundation, the seven pupils had their schools changed to regular schools.
Table 3: Type and Degree of Hearing Loss among the Participants

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Figure 1: Sample audiogram of a pupil

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  Discussion Top


Many pupils attending the deaf schools commonly have congenital deafness; this morbidity may be compounded by the presence of other congenital abnormalities. There was a slight male predominance among the subjects studied with a male-to-female ratio of 1.29:1. This finding was similar to an earlier study by Shuaibu et al.,[10] which assessed the hearing level of students of similar schools, reported a male: female ratio of 1.4:1. A few cases of stenotic external auditory meatus were seen in this study. Three cases of bilateral isolated atretic external ear canal were seen among the pupils. For congenital external auditory canal atresia, an incidence of 1 in 10,000 live births to 1 in 20,000 live births has been reported.[15],[16] Souradeep[17] found that nearly 75% of participants with microtia had associated congenital external auditory canal atresia of varying degree. Iseh et al.[18] in Ibadan Southwestern Nigeria found meatal atresia associated with microtia in 10 patients and isolated cases of meatal atresia in two patients. Congenital external auditory canal atresia can be fibrous, bony or a combination of the two (mixed) and there can be associated middle ear abnormality with resultant conductive deafness. Almost a third of congenital external ear canal atresia involves both ears with overt male preponderance, mostly seen among right ears.[19]

In this study, 19 (4.4%) participants had tympanic membrane perforation and this finding was lower than the 7.2% documented by Ahmed et al.[20] in the same school in an earlier study. The difference in the frequency of tympanic membrane perforation between the present study and that of Ahmed et al.[20] could be because they assessed pupils in only the government school, while the present study assessed pupils in both the government and the private deaf schools. Adhikari et al.[21] in Nepal found perforated tympanic membrane in 5.7% of school going children in Nepal. Ibekwe and Ogechi[22] in Port Harcourt South-southern Nigeria while assessing for ear diseases in patients attending Ear, Nose, and Throat specialist clinic found that nearly 12.0% of the patients had perforated tympanic membranes. This documented a higher rate of tympanic membrane perforation may be because subjects studied already had otologic complaints warranting them to seek for medical attention.

The PTAVs revealed that almost 99% of the subjects had bilateral profound sensorineural hearing loss; however, 1% of the subjects studied were noted to have serviceable hearing. One ear had moderately severe sensorineural hearing loss while eight ears had severe sensorineural hearing loss out of which two pupils had bilateral affectation. Among the subjects, one pupil was found to be using bilateral in the canal hearing aid. He was found to have bilateral preauricular sinus and a right branchial fistula discharging clear saliva. His audiogram showed bilateral severe sensorineural hearing loss. However, he had no other visible congenital abnormalities. Such a pupil will benefit from imaging of the urinary system in the form of an intravenous urogram or ultrasonography of the kidneys to check for the presence of renal abnormalities. This could have given a clue to the possibility of branchio-oto-renal syndrome in that pupil.

Ahmed et al.[20] found all the students assessed to have profound hearing losses. Shuaibu et al.[10] found profound hearing loss in 87.3% of the deaf pupils studied, while 12% were found to have varying degree of potentially serviceable hearing losses, 0.7% of their participants were found to have normal hearing. Ahmad et al.[23] studied deaf pupils aged between 5 and 15 years old in Ibadan and found 70% of the pupils to have serviceable hearing losses. The wide difference in the proportion of deaf pupils with serviceable hearing losses between Ahmad et al.'s study and the present study could be because of the difference in periods where the two studies were carried out; the studies were almost 20 years apart. Another possibility could be that during the previous study, pupils were not thoroughly being screened and fully evaluated by a Specialist Otolaryngologist before enrolment into deaf schools. This finding of pupils in a deaf school with serviceable hearing suggests the need for pre-admission and periodic hearing assessment in the deaf schools so that affected pupils can be rehabilitated and integrated into normal schools.

It is pertinent to note that when a pupil is seen with a congenital external ear abnormality, other congenital abnormalities should be sought out for, with the sole aim of identifying some syndromes and associations that could be a pointer to more life-threatening conditions such as congenital heart defects such as ventricular septal defects. Other life-threatening conditions such as renal hypoplasia should also be evaluated for with analysis of the serum electrolytes and urea as well as ultrasonography of the kidneys or an intravenous urogram. Such life-threatening conditions could lead to morbidity and mortality in such pupils, hence identifying them and treating them is key to sound health among such pupils.


  Conclusion Top


This study showed that the hearing thresholds in majority of the deaf pupils were bilateral, profound, sensorineural hearing loss and mostly affecting higher frequencies. About 1% (1.0%) of the deaf pupils had a serviceable hearing and were rehabilitated and enrolled into regular conventional schools.

Acknowledgement

We wish to acknowledge Dr. Umaru Sambo Grema of Department of Clinical Services, National Ear Care Centre Kaduna-Nigeria, for borrowing us his diagnostic Audiometer free of charge.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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