[Diagnosis of hearing disorders in children with early evoked auditory brainstem potentials].

BACKGROUND

Early Brainstem Evoked Response Audiometry (BERA) is a modern noninvasive, objective neurophysiological method for evaluation of hearing threshold. This method is applied in the complex otoneurological diagnostic procedure. The aim of the complete functional diagnostic procedure of hearing impairment in children is to determine the hearing level for the purpose of an early, adequate and quality hearing stimulation which affects the morphophysiological development of the complex auditory system. There are programs for early detection of the hearing impairment which give high-risk register. The registry consists of the following factors: family history of childhood hearing impairment, congenital perinatal infection, anatomical malformations involving the head or neck, birth-weight less then 1500 g, hyperbilirubinaemia, asphyxia with acidosis, usage of ototoxic drugs (high dosage of aminoglycosides). Hearing level is determinated by well-formed V wave on the lowest level of the stimulation intensity.

METHODS

The paper presents an analysis of the results obtained in the period January 1992-December 1995. The diagnostic procedure was applied in 89 children ranging from 9 months to 5 years of age. The children were checked due to suspicion of hearing impairment, because of pathological speech development (undevelop speech, low level of speech development, etc.). Children were hospitalized and a complete diagnostic procedure consisted of: detailed hetero-anamnesis, otolaryngological examination, surdopaedagogical anamnesis and observation; objective audiological diagnostic procedure: BERA, tympanometry and stapedial reflex. BERA was done in a silent, dark, sound and electric-proof room using a Madsen Electronic ERA 2250. In general anaesthesia four silver disc electrodes were put to the vertex, both ear lobes and forehead of the child. Acoustic stimulation was done via earphones by monoaural stimulation by nonfiltrating click (frequency 1-4 kHz). We applied 2000 stimulations, with repetition rate 20/s. We started examination with the highest stimulation intensity--120dB, with decreasing steps of 10dB to the lowest intensity of stimulation with well-formed V wave. Tympanometry was done for evaluation of the middle ear status. The stapedial reflex was used as an indirect sign of hearing level.

RESULTS

At the ENT Clinic in Novi Sad during period January 1992-December 1995 89 children ranging from 9 months to 5 years of age, 55 males (61.8%) and 34 females (38.2%) were examined. We found positive family anamnesis (deafness/severe hearing impairment) in 11 cases (12.3%). The other risk factors were found in 25 (28.1%): preterm infants 12 (48%), hypoxia and asphyxia 6 (24%), usage of the ototoxic drugs 3 (12%), hyperbilirubinaemia 2 (8%), exsanguinotransfusion 1 (4%), hydrocephalus 1 (4%). During clinical examination we have found normal otomicroscopical findings in 80 children (89.9%) and in 9 children (10.1%) tubal dysfunction was found. BERA--normal findings were in 22 children (24.7%), mild hearing impairment in 8 (9%), moderate level in 9 (10.1%), severe hearing impairment in 47 (52.8%) and deafness in 3 (3.4%). Tympanometric curve type "A" was found in 76 children (85.4%), type "C" in 9 (10.1%) and type "B" in 4 (4.5%). Stapedial reflex was not registrated in 59 children (66.3%). Habituation procedure (hearing amplification and surdopaedagogical treatment) was applied in 51 children (57.3%) e.g. 86.4% of children with hearing impairment ranging from moderate hearing level to kyphosis.

CONCLUSIONS

Despite early beginning of the development of the complex auditory system damage, there are numerous nondetectable endogenous and exogenous factors. There are isolated hearing impairments or complex hearing impairments with damages of the other system and visible stigmata (syndrome). Well developed auditory function is a necessary precondition for speech development. (ABSTRACT TRUNCATED)