In edition 153 of BC Disease News we considered the recent NIHL judgment of Wignall and discussed the implications this had for common law dates of knowledge and implementation periods in NIHL claims. This week we look again at the judgment in relation to the court’s findings on causation.
NIHL has a characteristic audiometric pattern consisting of bilateral ‘notches’ or ‘bulges’ in hearing thresholds at 4 kHz – or 3 or 6 kHz4 (or any combination of these frequencies). If the noise exposure continues the notches/bulges deepen and spreads to affect the adjoining frequencies.5 It is generally accepted that NIHL usually begins around 4 kHz. At first it may be asymptomatic but if it spreads into the lower frequencies of 3 and 2 kHz, individuals begin to complain of hearing disability.6 In Scott-Brown’s Otolaryngology,7 Dr Alberti states that the loss at 4kHz usually begins to progress at a steady rate for about 10 years and then slows greatly. However, the loss eventually spreads into other frequencies and it may take up to 30 years to involve frequencies of 1kHz and below to any great extent. This will lead to a notched sensorineural hearing loss centred about 4kHz, gradually becoming a steeply sloping loss starting at about 0.5 kHz. This is illustrated in the following audiogram:
The effect of noise and the differing noise induced threshold shift by frequency is neatly demonstrated in the figure below reproduced from Noise and Man by W.Burns, 1968.
ISO 1999: Acoustics-Determination of occupational noise exposure and estimation of noise-induced hearing impairment, also demonstrates the maximal damaging effects of noise at 4 kHz. The table below shows the estimated (median) noise damage at differing frequencies as a function of exposure time (in years) and a daily noise exposure dose of 95 dB(A), LEP,d.
The 2012 Guidance Statement on the principle characteristics of occupational NIHL authored by the American College of Occupational and Environmental Medicine provides a useful outline of what NIHL typically looks like. 1 In relation to the frequencies affected, it states:
This approach is also propounded in the Report of the Expert Hearing Group,9 entitled ‘Hearing Disability Assessment’, in which it states NIHL has a recognisable audiometric pattern with the maximum damage usually occurring at 4,000Hz, but occasionally it may occur at 3,000Hz or 6,000Hz.
Moreover, the CLB Guidelines,10 for the diagnosis of NIHL, have, as one of the requirements that must be met for a diagnosis of NIHL , that there be evidence of a high frequency sensorineural hearing impairment i.e. that the HTL at 3, 4 or 6kHz is at least 10 dB greater than the HTL at 1 kHz or 2 kHz.
Conversely, when an individual is showing maximal losses at 1 kHz and 2 kHz, this may indicate that the individual is suffering from what is known as ‘cookie bite’ hearing loss. The condition affects the mid-frequency sounds but in most cases does not affect high and low frequencies. The condition derives its name from the specific form of the hearing curve in the audiogram of a person suffering from this particular kind of sensorineural hearing loss. An audiogram carried out on a person thought to have cookie bite hearing loss can be seen below:
This condition is relatively rare and is thought to have a genetic cause rather than indicative of NIHL. It is very rare for cookie bite hearing loss to be caused by damage to hearing. Those suffering from this condition will experience difficulty hearing the mid frequencies but not the low and high frequencies.
As such, it is established medical convention that where hearing loss has been caused by exposure to excessive noise there will be maximal damage at the frequencies of 3, 4 and 6 kHz. Where an audiogram is showing maximal loss at 1 or 2 kHz, this kind of loss is very rarely caused by damage and is more likely a genetic condition idiopathic to the individual.
However, in the recent decision of Wignall, the contrary was found.
Wignall v Secretary of State for Transport
We outlined, in detail, the facts of the case in Wignall in edition 153 of BC Disease News and as such for the sake of brevity we will not repeat those in any great detail, except to remind readers that the parties in this case were in dispute as to limitation, breach of duty, causation, quantum and apportionment of damages. The exposure in this case was said to be between 1957-1968.
The court posed two questions, firstly was the deceased’s hearing loss, revealed in 2 audiograms taken in October 2012 and February 2014, noise induced? Secondly, if it was, was the loss attributable to the defendant’s breach of duty?
The claimant relied upon the medical opinion of Mr Zeitoun, Consultant Otolaryngologist, Head & Neck Surgeon and the defendant relied upon that of Mr Jones, Consultant Surgeon formerly of the Department of Otolaryngology, Head & Neck Surgery. For the purposes of Mr Zeitoun’s medical report a pure tone audiogram was obtained on 18th October 2012 and for the purposes of Mr Jones’ report a further pure tone audiogram was obtained on 18th October 2012 and for the purposes of Mr Jones’ report a further pure tone audiogram was obtained on 18th February 2014. The appearance of these audiograms were similar and both demonstrated a hearing loss at the 2 kHz frequency which was greater than that at the 3 kHz and 4 kHz frequenciesparticularly in the right ear.
Both experts agreed that this was an unusual appearance for NIHL, however, Mr Zeitoun claimed that he would expect to see and had seen such a presentation in 5 to 15% of NIHL cases. In order to show that NIHL can affect the 2 kHz frequency Mr Zeitoun relied on the text book, ScottBrown’s Otolaryngology, as mentioned above, which states:
‘Noise-induced permanent threshold shift usually commences between 3 and 6 kHz, often around 4 kHz, and gradually worsens at that frequency and spreads into neighbouring frequencies. At first it may be asymptomatic but if it spreads into the lower frequencies of 3 and 2 kHz complaints begin’.
He also pointed out that the CLB Guidelines also refer to involvement at 2 kHz in some cases.
Mr Jones disagreed and expressed the opinion that the audiograms did not show evidence of NIHL at all because, as a point of principle, hearing losses most marked at 2 kHz are not evidence of NIHL. In doing so, he relied upon the position paper, also mentioned above, of the American College of Occupational Medicine, which summarises the typical features of NIHL and emphasised the sentence ‘there is always far more loss at 3, 4 and 6 kHz than at 0.5, 1 and 2 kHz’ and ‘the greatest loss usually occurs at 4 kHz’.
Mr Jones also relied upon the publication called ‘Advances in Noise Research ‘(1998), written by Dr Luxon, which he claimed endorsed the American criteria to the same general effect. However, HHJ Butler pointed out that Dr Luxon also accepts that NIHL ‘can begin in frequencies other than the 3-6 kHz region’ albeit ‘this is rare’.
Additionally, Mr Jones claimed that if one was to use the CLB Guidelines on such an atypical loss that it would result in a ‘false diagnosis’.
Mr Zeitoun did not agree with Mr Jones and insisted that whilst the audiogram was atypical it was still within the methodology of the Guidelines. However, he did accept that if the atypicality had included the 1 kHz frequency he would then not have diagnosed NIHL.
His Honour Judge Butler did recognise that the Guidelines indicated that the normal or typical presentation is of a measurement of hearing threshold level at 3, 4 or 6 kHz which is at least 10 decibels greater than that at 1 or 2 kHz. However, he emphasised at para 64 that:
‘It is in my judgment important to bear in mind that guidelines are just that. They are guidelines not a straightjacket. The express purpose of the guidelines is said (page 281) to be:
“…to assist in the diagnosis of noiseinduced 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”’.
HHJ Butler also acknowledged that the guidelines mainly referred to ‘uncomplicated cases of NIHL’, or ‘typical’ NIHL alongside ‘normal’ ageassociated hearing loss (AAHL). However, he concluded that:
‘In my judgment, this plainly does not mean that the guidelines cannot be applied to complicated cases where the NIHL is atypical or the AAHL is abnormal, merely that the expert using the guidelines should recognise the atypicality or abnormality’.
He went on to say:
‘No doubt in some cases the atypicality and the degree of abnormality would be such as to prevent an expert using the guidelines but I am satisfied on the balance of probabilities that Mr Zeitoun did not find himself in that position. In my judgment he has interpreted the guidelines as a guide not a rigid rule’.
In conclusion, HHJ Butler pointed out that Mr Jones’ position that NIHL could never be diagnosed where there was maximal loss at 2 kHz in any circumstances, did not accord with the publications. He noted that in the CLB Guidelines, Dr Luxon’s publication and Scott-Brown’s Otolaryngology text book, it had been said that maximal loss at 2 kHz in NIHL claims was rare.
Additionally he stated that if the CLB Guidelines were to be accepted as the definitive approach in the medico-legal context of NIHL claims then it had to be accepted that whilst atypical, maximal loss at 2 kHz can sometimes, in a small proportion of cases, lead to a finding of NIHL.
As such, HHJ Butler found that Mr Zeitoun’s evidence was preferred stating at para 70 that:
‘For all the foregoing reasons, I found the opinion of Mr Zeitoun to be logically consistent and his use of the guidelines and his approach to the audiogram results to accord with the orthodox medico-legal approach. Each case depends on its own facts and the quality of the evidence adduced. In the context of this present case, on the evidence presented to me, I reject Mr Jones’ opinion that where the greatest loss is at 2 kHz, NIHL cannot ever properly be diagnosed. I accept the opinion of Mr Zeitoun that although the deceased was atypical and his, NIHL in his case could properly be diagnosed, albeit as a rare or minority cases, subject to proof of hazardous noise exposure has been proved. The position is that, on the facts of this case, such exposure has been found proved.’
HHJ Butler, also rejected Mr Jones’ alternative argument that the cause of the hearing loss in both audiograms was idiopathic or had a genetic cause which was currently beyond scientific explanation. As such it was found that on the balance of probabilities the deceased’s employment was causative or materially contributory of part of his NIHL.
Conclusion and Comment
Most, if not all, of the medical and scientific literature on NIHL concurs that where typical occupational noise exposure gives rise to NIHL, then such losses are maximal at 4 or 3 or 6 kHz. However some of the literature also acknowledges a possibility, in exceptional circumstances, of maximal loss at 2 kHz. Although generally for the hearing at 2kHz to be affected by NIHL it would take over twenty year’s exposure, high noise levels and a sensitive ear for this to happen. As this was not the case in Wignall, it would seem more logical that the loss at 2 kHz was therefore not due to noise exposure but instead idiopathic i.e. of unknown origin.
As was recognised in Wignall, such a dispute as this is often determined on the evidence before the court. As such it is important that when faced with such a dispute, there is a focus on providing evidence to show that the individual does not fall into the ‘rare’ category and a specific alternative causative explanation for the hearing loss is put forward.