Sensorineural hearing loss in Nigerian children with sickle cell disease

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Summary

Aim:

To study the prevalence and pattern of sensorineural hearing loss (SNHL) in Nigerian children with sickle cell disease (SCD).

Materials:

Fifty-two children with SCD were assessed. Otologic examination and audiometric tests wee performed. There were 36 males and 16 females. Their age ranged from 6 to 19 years.

Result:

Seven children had hearing impairment. After hemoglobin categorization, all the SCD patients were found to belong to the homozygous (HbSS) group. There were no HbSC nor other variants detected. Prevalence of SNHL was 13.4% in these patients but the general population prevalence rate found in a control group was 6.2%.

Conclusion:

SCD has many organ manifestations and complication among which is sensorineural hearing loss. Regular audiologic assessment, counselling and rehabilitation of these patients with hearing aids are recommended.

Introduction

Sickle cell disease (SCD) is primarily a hematologic and genetic disorder, with multiorgan manifestations [1], [2]. It covers a group of conditions in which pathology may be attributed to the presence of sickle shaped red cells.

In SCD there is a substitution of glutamic acid with valine in the sixth position of B-chain of the hemoglobin. This term encompasses homozygous type (HbSS), variants such as sickle cells C disease (HbSC) and the sickle cell thalassemia as (HbSB-Thal). The heterozygous type of HbS types (HbAS) does not cause a disease [3], [4].

Sickle cell disease results from the abnormal hemoglobin (HbS) which in the homozygous state (HbSS) is known as Sickle Cell Anemia. The red cells of individuals with the mutant homozygous gene (HbSS) become sickle shaped in low oxygen tension pressure with reduced oxygen carrying capacity [5]. The basal turn to the cochlea is particularly sensitive to anoxia, due to the high oxygen consumption rate of the stria vascularis and poor capacity for anaerobic metabolism. Therefore with anoxia the basal turn which records high frequencies is first affected before the apical turn which is the seat of low frequencies. This is the usual pattern observed in hearing loss in SCD patients. Hearing loss manifests first in the basal turn (high frequencies) then in the apical turn (low frequencies) and then throughout the entire cochlear.

A low-grade continuous venous thromobotic process affects the cochlea in a similar way [6], [7]. Morgenstern and Menace [8] in 1967 propagated a theory that compression of the auditory canal, by the expanded bone marrow of the petrous temporal bone could contribute to hearing loss. Ischaemic damage to the hair cells of organ of corti of the cochlear, as a result of microthrombotic occlusions in the cochlear venous system seem to be another important cause of sensorineural hearing loss. These microthrombotic occlusions of distal capillaries can lead to anoxia and ischeamic necrosis in many organs. Neurologic symptoms (hemiplegia), several cardiovascular manifestations, impaired visual and auditory functions, acute mental syndrome, vertigo, osteomyelitis, recurrent infections, hepatomegaly, splenomegaly are all manifestations of sickle cell disease. Data in Nigeria shows that 2 out of every 100 young babies have sickle cell disease [7]. Sensorineural hearing loss (SNHL) is one of the several complications of this disease [9], [10] and has been found to occur in 8% of SCD children in Nigeria [11], 12% in USA [12], 22% in Jamaica [5], 36.5% in Kenya, [13] 60% in Ghana [14].

The aim of this study was to determine the prevalence and pattern of hearing loss in a group of children with sickle cell disease in Enugu, Nigeria. Several authors (Culberston, Updike, Davis) [15], [16], [20] had noted the influence of impacted cerumen and chronic otitis media as some of the causes of poor reading skills and poor school performance in children. This paper studies the prevalence and level of impacted hearing among young sickle cell patients. The result of the paper will reinforce the need for intensive premarriage counselling for future partners to reduce the birth of sickle cell children.

Section snippets

Study design

The hearing profile of 52 sickle cell patients who were randomely recruited from the sickle cell clinic of the department of pediatrics of the University of Nigeria Teaching Hospital Enugu was estimated. They were 36 males and 16 females with age ranging from 6 to 19 years. Another 52 children, AA genotype in the same group were recruited from a school at Ogbete Enugu as control group.

Examination

All the children had otoscopic and throat examination done by the first author. The pure tone audiometric tests (PTA) were conducted in a sound isolated audiometric room at frequencies 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 6, 8 kHz by the chief audiometrician using a duly calibrated Midimate 622 pure tone Audiometer. The ambient sound in the test room was >35 dB.

The patients were classified as having either normal hearing with threshold <25 dB, or hearing impairment with threshold >25 dB. All the

Results

Hearing loss found was categorised into mild, moderate and severe, profound types. The audiograms were also analysed into conductive, sensorineural and mixed hearing loss. Any hearing threshold >25 dB was considered as normal, while <25 dB was hearing impaired. The hearing threshold for each frequency obtained by averaging.

The age distribution of the patients is shown in Table 1, and the age distribution of the patients with sensorineural hearing impairment is shown in Table 2. Of the 52

Discussion

Results of this study indicate that five patients (71.4%) had a SNHL at four frequencies 500–6000 Hz while two patients (28.5%) had SNHL loss only at 800 Hz. This finding contrasts with those of Friedmann et al. [4] and Todd et al. [5] who found that sickle cell disease is complicated initially by a high frequency hearing loss and later on by a generalized endocochlear hearing loss. Prevalence of hearing loss in SCD patients 13.4% was higher than in the general population (6.2%). Another author

Conclusion

We therefore recommend premarital counselling and blood tests (genotype) to reduce the incidence of sickle cell disease. More studies should be undertaken on the impact of SCD in the inner ear structures of children.

Acknowledgement

Our gratitude goes to Mr. N.O. Nwaogbo, the Chief audiometrician for his assistance during the study.

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