Portuguese Version

Year:  2003  Vol. 69   Ed. 6 - (9º)

Artigo Original

Pages: 785 to 789

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Evaluation of the five wave from auditory brain response of children who not passed in neonatal screening

Author(s): Viviane Camargo Marques1,
Luis Miguel
Chiriboga Arteta1,
Elaine Soares2

Keywords: neonatal screening, brain auditory , V wave

Abstract:
It is very well established the importance of early diagnostic of hearing loss. Everybody speaks about neonatal screening, but just a few people comment about the children who not passed on screening. The auditory brainstem response (ABR) is the next step of the diagnostic. The aim of this paper is evaluate the ABRs from children who not passed on screening, looking for the threshold and the latency of the five wave. Study Design: Clinical prospective. Material and Method: 75 ABR were analyzed. Results: A great number of exams was normal. The most frequently alteration was the increase of the latency of the wave V that can be explained for the incomplete mielinization from the auditory pathway, otitis media or retrococlear alterations. Conclusions: We concluded that the increase of the latency of the V wave is the mainly alteration on ABRs.

INTRODUCTION

The first years of life are considered critical for the development of hearing and language. Early diagnosis and intervention are essential for the development of children with hearing loss 1-4.

Much has been said about the importance of conducting neonatal hearing screening right after birth 1, 5-10. The moot used objective methods are otoacoustic emissions (OAE) and auditory brainstem response (ABR) 9-14.

OAEs have been widely indicated in screening programs since they are quick, easy to apply and can reach a large number of subjects within a short period of time 1, 6, 10, 12, 16, 17.

ABR has been the method of choice for early diagnosis of hearing loss for years now. It is a sensitive and specific method, but more complex, takes longer to perform, and has a very high initial cost of the device 13, 18-21. It is more complicated to use it as a screening tool, especially because of the time it takes to conduct the test and the high price of the device. Automatic ABR has been suggested for use in hearing screening, since it is quicker, but the cost of the device is still very high for Brazilian centers 22-25.

Equally important to screening are follow-up and early diagnosis of hearing disorders in children who fail screening 4, 26, 27-30.

In our center, children who are tested and fail are referred to the Otorhinolaryngologist and after having solved possible affections such as cerumen build-up or vernix in the external acoustic canal, they are retested and if they fail again, then an ABR is conducted.

The purpose of the present study was to check what are the most frequent affections of ABR in this population and to check the compliance of the population to neonatal hearing screening.

Material and Method

In the period between December 1999 and March 2002, we performed 5,835 OAE assessments in the neonatal hearing screening center of the institution. Out of the total, 360 children were referred to the ENT doctor for complete ear exam and retested after it. After OAE retest, 128 were referred to ABR and 75 came to be tested.

We analyzed the ABR of 75 children who came to be tested after having failed OAE in the hearing neonatal screening.

OAE were conducted in an acoustically treated room, using equipment ILO 2.92 Otodynamics Ltda.

ABR was conducted while the child was asleep, if necessary under sedation with chloral hydrate 14% 0.5ml/3Kg weight. We used a two-channel device Smart EP by Intelligent Hearing System.

The used parameters were low pass 1500 Hz, high pass 100 Hz; rarefaction click stimulus; 1024 stimuli to 17.7 stimuli per second; insertion phone or bone oscilloscope in cases of microthia 19.

We considered normal auditory electrophysiological thresholds as intensity of 30dB HL corresponding to 15 dB psychoacoustic threshold. Mild hearing loss - thresholds between 40 and 50 dB (HL); moderate hearing loss - thresholds between 60 and 70 dB (HL); severe - thresholds between 80 and 90 dB(HL), and profound - thresholds above 90 dB(HL).

We analyzed electrophysiological thresholds using ABR in both ears. Next, we analyzed wave V latency 30dB over the thresholds in each ear, whenever possible, but for thresholds over 70dB, latency was obtained in intensity greater than 20, 10 or the threshold, since maximum device intensity was 100dB (HL).

In the present study, we did not assess amplitude of wave V and latency-amplitude of the other waves. Children with alterations in the ABR were instructed to come back for retest 2 months later. This study addressed the first test conducted. A next study is going to address the second ABR performed.

Results

ABR was conducted in 75 children (150 ears).

Graph 1 shows distribution of the population by age and gender.

Auditory electrophysiological threshold in the tested ear, by number of ear, is shown in Table 1.
Table 2 shows the behavior of wave V concerning latency in different age groups (below 30 days, 12-3 months, 3-6 months, 6-9 months, 9 months to 1 year).

We noticed that most of the kids presented ABR within normal ranges. Most tested ears (61 ears or 40.67%) presented electrophysiological thresholds at 30dB HL. In 55 ears (36%) we found mild hearing loss, in 22 (14.6%) moderate hearing loss, in 6 (4%) severe hearing loss, and in 6 ears (4%), profound hearing loss.

The assessment of wave V latency proved to be increased in 64 ears (42.67%), which suggested conductive or retrocochlear hearing loss. A percentage of children (10%) presented latency values expected for adults. Seven ears (4.67%) did not present responses.

Graph 1. Distribution of children submitted to ABR by age and gender.



Table 1. Electrophysiological thresholds on the right and left ear.



Table 2. Behavior of wave V concerning age and number of ears (open age range on the right).

Discussion

Hearing is essential for the acquisition and development of speech and language. Studies confirmed that detection of auditory abnormalities and intervention that begins before the age of 6 months ensure development of expressive and comprehensive language, as well as social development compared to that of normal children in the same age range 2, 3. To that end, the process of detecting auditory disorders should begin with neonatal hearing screening followed by early diagnosis and intervention. The first six months of life are decisive for the future development of the hearing impaired child 3.

After hearing screening, conducted at the nursery, it is necessary to have complete diagnosis in case of screening failure. It is essential that other tests, such as auditory brainstem response, immitanciometry and auditory behavior observation be incorporated by the otoacoustic emission test so that the diagnosis of hearing impairment can be concluded 16, 28.

Professionals have gradually become aware of the importance of early diagnosis of hearing loss for global and social development of children. The same has not happened to lay people yet 16, 24.
Neonatal hearing screening in our city is not mandatory. Our service provides the exams to all children born in the center, both for public and private healthcare coverage. Most of the families do not ask for the examination, delaying the auditory assessment of the child.

Other parents are instructed to come to a second examination owing to the presence of vernix, which leads to failure in the first test. Many children are never brought back. Similarly, not all children referred to the division of ENT are taken to the visit. Others go to the medical visit, but do not come back for retest. The same applies to the performance of ABR. Patients' drop out rate explains the high number of ABRs that are conducted in more advanced ages.

We noticed that ABR was normal in most of the children that had failed otoacoustic emissions 9, 19, 29.
The most commonly found affection in ABR was increase in latency of wave V, which may correspond to delay in electrical conduction by the still undergoing process of myelinization 18, 27 since processing of acoustic information at about 2 years and six months equals that of adults, whereas wave V is still maturing up to the age of 2 years. Another factor would be retrocochlear or conductive loss 19. Normally, the conductive affection most commonly found in this age range is conductive loss by middle ear secretion 28. It should be confirmed by the performance of tympanometry; if present, it should be immediately treated.

The follow-up of these children should continue up to conclusion of the case2,3.

Conclusion

1- Many patients are lost during the steps of the hearing screening protocol, delaying or hindering correct and early diagnosis.
2- Most of the children that fail in OAE have normal auditory electrophysiological thresholds.
3- The most frequent ABR affection was wave V latency increase.

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1 Physician, Service of Otorhinolaryngology, Maternidade de Campinas.
2 Speech Therapist and Audiologist, Service of Neonatal Hearing Screening, Maternidade de Campinas.
Study conducted at Maternidade de Campinas.
Address correspondence to: Dra. Viviane Camargo Marques - Rua Cristovão Colombo, 185/ 121 Campinas SP 13023-230.
Tel (55 19) 3234-1017
Study presented as Free Communication at 36º Congresso de 2002.
Article submitted on February 07, 2003. Article accepted on October 16, 2003.

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