Guidelines for quantification of noise-induced hearing loss in a medicolegal context.

OBJECTIVES: Guidelines published in 2000 by the authors are widely used by medical and legal professionals in the UK for diagnosis of noise-induced hearing loss in a medicolegal context. However, they cannot be used for quantification of the noise-induced hearing loss, which is required in most cases. This requirement is addressed. DESIGN: A method is developed here to quantify noise-induced hearing loss, thereby overcoming this shortcoming. SETTING: Assessment of noise-induced hearing loss in medicolegal cases. PARTICIPANTS: A consecutive series of 124 cases of noise-induced hearing loss is used for evaluation. MAIN OUTCOME MEASURE: Magnitude of noise-induced hearing loss based on hearing threshold levels averaged over the frequencies 1, 2 and 3 kHz. RESULTS: The rationale of the method, practical application and three worked examples are developed. A simpler short-cut method is developed and shown to be equivalent to the full method in most cases. CONCLUSIONS: The method offers a practical approach to quantification of noise-induced hearing loss.

Guidelines on the diagnosis of noise-induced hearing loss for medicolegal purposes.

These guidelines aim to assist in the diagnosis of noise-induced hearing loss (NIHL) in medicolegal settings. The task is to distinguish between possibility and probability, the legal criterion being 'more probable than not'. It is argued that the amount of NIHL needed to qualify for that diagnosis is that which is reliably measurable and identifiable on the audiogram. The three main requirements for the diagnosis of NIHL are defined: R1, high-frequency hearing impairment; R2, potentially hazardous amount of noise exposure; R3, identifiable high-frequency audiometric notch or bulge. Four modifying factors also need consideration: MF1, the clinical picture; MF2, compatibility with age and noise exposure; MF3, Robinson's criteria for other causation; MF4, complications such as asymmetry, mixed disorder and conductive hearing impairment.

Visual impairment in severe and profound sensorineural deafness.

The frequency of reversible and irreversible visual impairment was determined in children with severe and profound sensorineural deafness, as subnormal vision can adversely affect their educational and social development. Eighty three of 87 such children attending an audiology service were examined to assess the incidence and severity of visual impairment. Each child underwent a detailed ophthalmic assessment. The criteria for visual impairment were visual acuity < 6/9 Snellen or equivalent and/or abnormal binocular vision. Forty five had a normal ophthalmic examination (54.2%). Twenty nine had visual impairment (34.9%) and nine had ophthalmological abnormalities that did not interfere with vision (10.9%). A higher proportion of children with risk factors for visual pathology demonstrated visual impairment than those in whom there were no risk factors. None the less, 44% of visual impairment was among patients without risk factors. The results underline the need to examine all children with severe and profound sensorineural deafness soon after diagnosis and indicate that children with multiple handicaps have a greater likelihood of visual impairment (11 of 14 cases).

Evaluation of click-evoked oto-acoustic emissions in the newborn.

Click-evoked oto-acoustic emissions and auditory brainstem responses (ABR) have been recorded in 723 babies taken largely from a neonatal intensive care unit to evaluate the use of oto-acoustic emissions as a method of screening for hearing impairment. Twenty-nine infants failed to pass the initial ABR test and repeat ABR tests carried out up to the age of 3 months. The 'sensitivity' and 'specificity' of the oto-acoustic emission test for the ABR test results up to 3 months of age in surviving infants were 93% and 84% respectively. It is proposed that click-evoked oto-acoustic emissions be considered as the initial method to screen for hearing impairment, test failures being followed up by ABR.

The effect of stimulus level on click evoked oto-acoustic emissions and brainstem responses in neonates under intensive care.

Click evoked oto-acoustic emissions (EOAE) at a range of stimulus levels and the auditory brainstem response (ABR) threshold have been measured in 40 infants admitted to a neonatal intensive care unit (NICU). The stimulus levels at which the emissions were first observed had a similar mean value and distribution to those found in previous studies on normal newborns and young adult volunteers. The difference was in the proportion who had no detectable emissions, 16.7% as against 3.9% in the normal newborns and 2.6% in young adult volunteers. The distribution of thresholds for the ABR was again similar to those measured on normal newborns but 8.1% of the ears of the NICU infants had a threshold worse than 53 dBnHL compared with 0% for the normal newborns. A combined screening method starting with the click evoked oto-acoustic emission is proposed. A comparison of the mean ABR thresholds for those in whom an EOAE was recorded to those with no EOAE showed a group effect. The stimulus latency relationship of the NV peak showed too much variation between individual results to consider its use to define accurately the degree of conductive hearing loss.

Click evoked otoacoustic emissions in neonatal screening.

Seven hundred and twenty-three neonates under intensive care have been tested by evoked otoacoustic emissions (EOAE) and the auditory brain stem response (ABR) to investigate the use of EOAE as a test for hearing impairment. Three hundred and thirty-one have had follow-up tests to the age of at least 2 years. The EOAE test has been found to be practical and quick to perform. The proportion of NICU infants producing a recordable EOAE is 80%, and the sensitivity and selectivity to the ABR result in the period up to 3 months post due date is 93 and 84%, respectively. These figures are high enough and the reduction in time compared to ABR is sufficient for the EOAE to be considered as the primary screen. The follow-up data show mixed results with both false positives and false negatives present. The incidence of severe hearing impairment is close to that expected from retrospective studies at 2 in 331 (1 bilateral, 1 unilateral). Firm conclusions on the sensitivity of EOAE to long-term hearing impairment await the results from larger numbers of infants and further follow up data.

Click evoked otoacoustic emissions compared with brain stem electric response.

The hearing of 346 babies taken largely from a neonatal intensive care unit has been tested by otoacoustic emissions and brain stem electric response audiometry. A total of 336 (97%) of the babies have been followed up by hearing tests from the age of 8 months. The otoacoustic emission test has been found to be practical with a mean test time of 12.1 minutes compared with 21.0 minutes for brain stem electric response. An otoacoustic emission was recorded bilaterally in 274 (79%) babies. Twenty of the 21 surviving infants who failed brain stem electric response in the neonatal period did not produce an emission. It is concluded that the otoacoustic emission test would make a good first screen to be followed by the brain stem electric response if no otoacoustic emission was present. There is poor agreement between the test results in the neonatal period and those of the follow up period, however, indicating the need for continuous monitoring of those babies failed by brain stem electric response.

Three-year follow-up (1983-1986) of children undergoing bilateral grommet insertion in Sheffield.

A retrospective study with review, after 3 years, of 43 children between the ages of 4 and 13 years, who had bilateral otitis media with effusion treated surgically purely by the insertion of grommets is described. The results shows that the younger the child at initial grommet insertion, the greater the likelihood of more than 1 grommet insertion being required (P less than 0.05). A younger patient is likely to make a greater number of outpatient visits (P less than 0.05), and the number of outpatient visits correlates with the number of grommets inserted (P less than 0.01). At 3 years, 49% of children remained on regular outpatient follow-up, while 34% of children had persisting effusion in 1 or more ears. Whilst grommets are in place, otorrhoea is not adversely influenced by swimming. The role of adenoidectomy in the management of otitis media with effusion is not assessed by this study.

A comparison of oto-acoustic emissions and brain stem electric response audiometry in the normal newborn and babies admitted to a special care baby unit.

Brainstem auditory evoked potentials and oto-acoustic emissions have been recorded in 30 normal newborns and in 112 infants admitted to a special care baby unit as part of a study to determine whether these tests can be used to detect the hearing impaired infant. All the ears tested in the normal newborns, where the infant was quiet enough to complete the test, produced a brain stem electric response at a stimulus level less than or equal to 53 dB nHL (dB relative to normal hearing) and 96% produced an oto-acoustic emission at the highest level tested of 41 dB nHL. The mean threshold of the oto-acoustic emission in the normal newborns was 17.7 dB lower than the mean brain stem electric response threshold. The range of thresholds were similar. In the special care infants 84% of ears produced a brain stem electric response at a screening level of 43 dB nHL and 81% of ears produced an oto-acoustic emission at a screening level of 31 dB nHL.

A comparison of transtympanic and ear canal recorded electrocochleography in clinical practice.

Electrocochleograms were recorded in a routine clinic on 21 patients by the transtympanic method and from a surface electrode in the ear canal. This was to determine whether a non-invasive technique would give the same clinical information as the normal transtympanic technique. Taking the transtympanic technique as the standard for comparison, the ear canal technique produced a significant number of errors in compound action potential threshold and width. The summating potential/compound action potential ratio could only be measured in just over half the ear canal recordings compared with the transtympanic recordings. From these results and a retrospective study of the notes looking at the effect of electrocochleography on diagnosis and management, it was concluded that the ear canal technique was not a substitute for transtympanic electrocochleography where the use of an invasive technique is justified.

Electrical response audiometry: a survey of its effect on the diagnosis and management of deafness in children.

The effect of the use of electric response audiometry (ERA) on the diagnosis and management of children has been investigated. A retrospective method was employed using the notes of the first 102 hearing assessments in 1978 where an ERA test was performed. The results show that the effect on diagnosis has been to improve the degree of certainty rather than to re-classify patients as deaf or normal. The effect on management has been to reduce by 24% the number of patients that require repeat assessment. These effects are more pronounced in the '0--1 age group' as opposed to the 'above 1 year' age group.