Assessment, localization of hearing loss and rehabilitation in children with cerebral palsy

INTRODUCTION

Cerebral palsy (CP) is defined as “a group of permanent disorders of the development of movement and posture, causing activity limitation, that is attributed to non progressive disturbances that occurred in the developing fetal or infant brain.”¹ The incidence of CP in the general population varies throughout the world at a rate of 0.1%–0.2% of live births in developed countries and is slightly higher in developing countries, with the risk of CP increasing with decreasing gestational age.^2,3

CP is commonly associated with a spectrum of developmental disabilities. Besides motor abnormalities, a child with CP suffers from multiple handicaps like mental retardation, epilepsy, visual, hearing, speech, cognitive, and behavioral abnormalities.⁴ There are few published studies on the prevalence of hearing loss in CP. The incidence of hearing loss was reported to be between 7% and 37.5%, with the majority of studies commenting only on sensorineural hearing loss (SNHL).^5–9 Lesions causing hearing loss potentially involve the organ of Corti, especially at the outer hair cells and the cochlear nerve.

Hearing loss, which is so commonly associated with CP, requires an audiological assessment for a definitive diagnosis.¹⁰ Such children who are not responsive can be tested for hearing loss using an auditory evoked potential that measures the lowest possible sound level, which produces a brain wave in the child.

Although SNHL in patients with CP has been known for more than 50 years, yet the site of lesion in these cases remains in controversy. Also, the assessment of hearing in CP patients has always been a difficult task. Both parents and treating physicians remain uncertain about the cause of deranged/no response to any auditory stimulus in these patients. Even in those cases where hearing loss is established, the location of lesion causing hearing loss remains uncertain. It is however possible with the spectrum of investigative means available with us now in the form of distortion product otoacoustic emissions (DPOAE), transient evoked otoacoustic emissions (TEOAE), brainstem evoked response audiometry (BERA), pure-tone audiometry (PTA), impedance audiometry, cortical evoked response audiometry (CERA), and functional magnetic resonance imaging(fMRI) to identify and evaluate the hearing loss and make an endeavor to locate the site of lesion in such cases.

Our patients were investigated by BERA, TEOAE, DPOAE. PTA and impedance audiometry were done in a few cases. BERA is an objective test to evaluate hearing threshold and to diagnose retrocochlear pathologies tests of the cochlear status, specifically outer hair cells.

MATERIAL AND METHODS

RESULTS

The distribution of neuromotor disturbance was studied. A maximum number of children (54%) with CP had quadriplegia, 21% hemiplegia, and 19% suffered diplegia. Spasticity was the most common type of neuromotor disturbance found in 91% of the children in this study group.

While 58.5% children passed on BERA according to our criteria, 41.5% failed the test [Figure 1]. The passing criteria used for BERA was the presence of wave V at 60 dB HL; 78% cases showed abnormal morphology of wave V. More than 50% cases that passed in BERA had poor morphology of wave V. Latency of wave V at 80 dB was prolonged in most cases [Table 1]. The mean latency of wave V was 6.159 msec [Table 2].

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Figure 1:

Result of BERA and OAE in all ears tested. BERA: Brainstem evoked response audiometry, OAE: Otoacoustic emissions.

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On otoacoustic emissions (OAE), 83.5% of the children failed the test according to our criteria and only 16.5% passed [Figure 1]. The passing criteria of TEOAE were: (a) The response was reproducible 50% of times the test was performed; and (b) Any of the three frequencies tested (1.0, 1.5, 2.0, 3.0, 4.0 kHz) had 3 dB more power in the response spectrum than the noise spectrum.

DISCUSSION

There are several issues in the assessment of hearing in children with CP and these include the objective test to be chosen as per needs of the child, reliability of these tests, degree of hearing loss, and its precise localization.

In our study, prevalence of hearing loss in children with CP was calculated from patients on the basis of children who failed on BERA. The prevalence was found to be 41.5%. However, the actual prevalence would still be higher because this does not take into consideration the cortical-level hearing loss. The exact prevalence of hearing loss can probably come only from CERA.

Topolska et al. in 2002 had performed audiologic examination on 32 patients. Their audiological testing comprised of impedance audiometry, DPOAE, BERA, and psychophysical studies—tonal and speech audiometry. They recognized hypoacusis in 37.5% of the children on the basis of psychophysical studies.¹¹ They could not perform tonal audiometry in 25% of the cases due to the mental status of the child. Hearing impairment affects a significant proportion of children with CP.

Weir et al. (2018) performed audiologic assessment of 940 patients and found hearing loss in 367 (39%).¹² They collected data from their AudGen Database, including pediatric patients with a diagnosis of CP. They collected data from the free field audiometry and ear-specific audiometry tests. According to this study, hearing loss of 15 dB or more on PTA or 20 dB by sound field audiometry was taken as significant. No BERA or OAE was done.

In most cases, there is evidence of involvement of cochlea, as OAE is absent in most cases (83.5%). Children who are BERA pass and OAE pass (14%) should hear normally. If they have hearing loss, it is because of a more central cause. Children who are BERA pass and OAE fail (44.5%) could have fluid in the middle ear or mild SNHL. Children who are BERA fail and OAE pass could have lesion at the spiral ganglion or brainstem or cochlear nerve. Children who are BERA fail and OAE fail (39%) could have purely cochlear or cochlear and brainstem/nerve involvement [Figure 2].

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Figure 2:

Pattern of results of all ears tested. BERA: Brainstem evoked response audiometry, OAE: Otoacoustic emissions.

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Taking BERA as gold standard, the efficacy of OAE was compared with it using the chi-square test. Chi-square value was 11.30 and p-value was 0. 0007. The difference between the two tests was statistically very significant. Hence, OAE was found to be a less efficacious test as compared to BERA in detecting hearing loss.

In the last few years, cochlear implants (CIs) have been developed for auditory rehabilitation of children having severe to profound hearing loss.¹³ Richard et al. (2021) did a systematic review and identified two interventions (hearing aid and cochlear implantation).¹⁴

Rehabilitation in the form of hearing aid or CI would be required in children who are OAE fail and BERA fail (39%), OAE fail and BERA pass (44.5%), and OAE pass and BERA fail (2.5%).

The children in our study group hardly ever got hearing aids fitted because parents were already occupied with multiple other handicaps of the child. Rehabilitation of hearing loss still remains an unachievable goal in such children with CP.

There are various issues in the assessment of hearing of children with CP. They are unable to speak and respond, so it becomes difficult to ascertain whether hearing loss actually exists. If the hearing loss is due to a defect in hearing pathway before the cortex, the child is expected to improve with hearing aids, CIs, or brainstem implants. However, if this is at cortical level, none of the above-mentioned devices would work. Hence, it is important to establish, quantify, and find the level of defect, and this is a difficult task.

CONCLUSION

The prevalence of hearing loss amongst CP children was calculated to be 41.5%. In most cases, the site of lesion was found to be cochlea, as OAE was absent in most of such cases (83.5%). OAE was found to be a less efficacious test as compared to BERA in detecting hearing loss.