Med Pr. 2001;52(5):305-13.     Related Articles, Links

    [Tinnitus in noise-induced hearing impairment]

    [Article in Polish]

    Kowalska S, Sulkowski W.

    Samodzielna Pracownia Otolaryngologii i Audiologii Instytut
Medycyny Pracy, Lodz.

    The analysis of the epidemiological data indicates that exposure to
noise is widespread and it is one of the most common causes of tinnitus,
estimated at about 20.7% according to Hazell; 28% according to Axelsson;
and 42% according to Palmer. Bearing in mind the scantiness of reliable
data on the incidence and nature of tinnitus in persons exposed to
industrial noise, and especially the need for the objectivity of this
subjective symptom, the authors have decided to undertake the study
aimed at assessing the interrelation between tinnitus, the magnitude and
kind of hearing impairment, and otoacoustic emission. The study group
included 191 persons aged 42.5 +/- 7.6 years (range, 25 to 65),
occupationally exposed to noise at the levels of 88-92 dB(A) for 26.9
+/- 4.6 years (range, 9 to 30) who had reported hearing disorders and
tinnitus. The control group, matched by similar age and duration of
employment, consisted of 80 persons with perceptive hearing impairment
induced by industrial noise who had not complained of tinnitus. *The
results of the study revealed that in 59.7% of the study subjects, noise
proved to be one of the most probable factors responsible for the
development of tinnitus.* The presence of tinnitus was found in 22.5%
and in 46% of the study subjects after 10 years and 11-20 years of noise
exposure, respectively. In 95.8% of workers, tinnitus was associated
with hearing loss, and only in 4.2% of cases it occurred in ears with
normal hearing. In persons exposed to noise, tinnitus was most
frequently (59.2%) bilateral and permanent. Following the audiologic
examinations, verified by objective audiometry (tympanometry, ABR),
cochlear hearing impairment was found in 68.6%; retrochochlear in 8.37%;
mixed and other forms of impairment, e.g. presbyacousis, in 19.4% of
subjects. The audiologic assessment of tinnitus demonstrated that in
62.3% of persons, tinnitus occurred at high frequencies and correlated
with the magnitude of hearing impairment in the tonal audiogram. The
tinnitus intensity ranged between 10-15 dB and 45 dB. *In 40.3% of those
under study, noise was not the only tinnitus-risk factor. In this group
of persons, the presence of predisposing diseases was also observed,
e.g. hypertension, diabetes, atherosclerosis, disturbed lipid metabolism
and other etiologic factors that might have impact on the tinnitus
incidence, ototoxic drugs, for example.* The measurements of evoked
otoacoustic emission (EOAE and DPOAE) revealed in 58.63% of persons
significant differences (p < 0.01) in the amplitude and spectrum of EOAE
in the ears with tinnitus as compared to the ears without tinnitus with
a similar hearing threshold. Whereas in 27.74% of subjects, no
differences in the EOAE measurements in the ears with or without
tinnitus were observed. The results of DPOAE measurements showed in 62%
of subjects significant differences in DP-grams in the ears with
tinnitus as compared to the ears without tinnitus (p < 0.01).
Interestingly, the differences in measurements of both types of evoked
emissions (EOAE and DPOAE), expressed by the lowered amplitude, narrowed
spectrum, reduction of emission or its complete fading in a limited area
of high frequencies, were demonstrated in the ears with tinnitus only in
retrocochlear hearing impairment, as compared to those free from
tinnitus. The evaluation of the EOAE and DPOAE measurements seems to
prove that this method may be useful in assessing the contribution of
the cochlear mechanisms to the incidence of tinnitus and in
distinguishing between tinnitus generated in cochlea and tinnitus with
the source at other levels of the hearing organ or beyond it. Our study
failed to determine the interrelation between tinnitus and spontaneous
emissions as the emission was registered only in about 12% of persons
exposed to noise, including 2% of those with normal hearing.

    PMID: 11828843 [PubMed - indexed for MEDLINE]

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