Evaluation of the monaurally evoked brainstem response in the diagnosis of sensorineural hearing loss

The auditory brainstem responses in patients with unilateral cochlear hearing loss

The aim of our study is to analyze changes occurring in the auditory brainstem response (ABR) according to stimulus parameters in unilateral cochlear hearing loss cases. Twenty-nine cases (14 male, 15 female) with unilateral sensorineural hearing loss (SNHL) were investigated. All cases had cochlear SNHL on one side whereas normal hearing on the other side. All cases underwent ABR testing with varying stimulus intensity levels and stimulus repetition rates (SRRs). Results were compared and their correlation with audiogram shapes investigated. As stimulus intensity levels decreased on both ears, latencies expanded and amplitudes decreased in all traces of ABR. Latencies of ears with cochlear hearing loss were observed to be longer than those in normal ears. Responses to SRR increases were similar on both ears. Audiogram shapes should be taken into consideration while performing ABR in order to address asymmetric SNHL. The interpretation of ABR changes with various stimulus levels may provide a better understanding of cochlear pathologies associated with hearing loss in the future.

Effects of sex, age and hearing asymmetry on the interaural differences of auditory brainstem responses

Healthy patients with asymmetric sensorineural hearing loss who had received examination of auditory brainstem responses (ABR) were gathered for retrospective analysis. The effects of sex, age and hearing asymmetry on the interaural differences of ipsilateral ABR were determined by multivariant linear regression. Our results showed that the interaural differences of ABR wave III and wave V latencies were significantly affected by hearing asymmetry but not by sex or age. However, in female subjects younger than 50 years, differences of III-V intervals could be negatively correlated with hearing asymmetry. We suggest that plasticity in the auditory brainstem in younger females might account for asymmetrical peripheral hearing in this group.

The effects of sensory hearing loss on cochlear filter times estimated from auditory brainstem response latencies

Derived-band auditory brainstem responses (ABRs) were obtained in 43 normal-hearing and 80 cochlear hearing-impaired individuals using clicks and high-pass noise masking. The response times across the cochlea [the latency difference between wave V's of the 5.7- and 1.4-kHz center frequency (CF) derived bands] were calculated for five levels of click stimulation ranging from 53 to 93 dB p.-p.e. SPL (23 to 63 dB nHL) in 10-dB steps. Cochlear response times appeared to shorten significantly with hearing loss, especially when the average pure tone (1 to 8 kHz) hearing loss exceeded 30 dB. Examination of derived-band latencies indicates that this shortening is due to a dramatic decrease of wave V latency in the lower CF derived band. Estimates of cochlear filter times in terms of the number of periods to maximum response (Nmax) were calculated from derived-band latencies corrected for gender-dependent cochlear transport and neural conduction times. Nmax decreased as a function of hearing loss, especially for the low CF derived bands. The functions were similar for both males and females. These results are consistent with broader cochlear tuning due to peripheral hearing loss. Estimating filter response times from ABR latencies enhances objective noninvasive diagnosis and allows delineation of the differential effects of pathology on the underlying cochlear mechanisms involved in cochlear transport and filter build-up times.

Brainstem auditory evoked responses in patients with tinnitus

Brainstem auditory evoked responses of 355 patients with uni- or bilateral tinnitus were recorded in order to evaluate the effect of tinnitus on the central auditory system. The amplitudes of waves I, III and V and the latencies of each wave and interpeak latencies were compared to those of a group of 129 controls with normal hearing. The study of the control group initially identified a certain number of concurrent parameters. The brainstem evoked responses of men and women evolved differently from the age of 30 years, latencies of I-III and I-V in men lengthening with age and those of women tending to shorten. The patient groups were therefore compared to a control group of the same sex ratio or of the same sex, half being between 30 and 56 years of age. The tinnitus patients were divided into three groups according to the side affected by tinnitus. Latencies and amplitudes in these groups differed significantly from those of the control group. In order to eliminate hearing loss, the most difficult concurrent factor and almost always associated with tinnitus, the results of individuals with symmetrical hearing loss were compared to those of the control group. Tinnitus was always associated with significant lengthening of 0-I and I-V latencies on the tinnitus-affected side, with a significant reduction in amplitudes of waves I and III, and sometimes of wave V, particularly in the group with left-sided tinnitus. Comparison of tinnitus patients with symmetrical and asymmetrical hearing by sex showed that tinnitus patients of all groups had lengthening of right and left 0-I latencies, apart from the women in the group with right-sided tinnitus, and significant reduction in amplitudes of waves I and III in women and of left III only in men. When hearing loss was asymmetrical and on the tinnitus-affected side, there was also lengthening of 0-I latencies on the tinnitus-affected side in both sexes and of ipsi- and contralateral I-V latencies in women. Right- and left-sided tinnitus was associated with additional differences between the three groups. Correlation coefficient study confirmed that 0-I, I- III and I-V latencies were independent of the mean degree of deafness, deafness at high frequencies and at frequencies around the tinnitus, up to a threshold of hearing loss of 40 dB, above which 0-I and 0-V lengthened in addition to tinnitus. On the other hand, whatever the frequency, tinnitus involved significant lengthening of wave I latencies and modification of the previously recorded amplitudes. Two groups of tinnitus patients could be distinguished: the first, with symmetrical hearing loss, with symmetrical normal latencies, apart from 0-I latencies and the amplitude of the wave on the tinnitus side, and the second with hearing loss predominant on the tinnitus-affected side, with different latencies on each side, 0-I being shorter on the unaffected side, I-III and I-V being lengthened on the unaffected side and 0-I being lengthened on the tinnitus-affected side. Moreover, as disturbances of brainstem evoked responses caused by tinnitus particularly affected waves I and III, the hypothesis of possible involvement of the efferent systems could be proposed.

Specificity of auditory brainstem response audiometry criteria in acoustic neuroma screening as a function of deviations of reference values in patients with cochlear hearing loss

On the basis of 79 patients with cochlear hearing loss, the statistical distribution of two criteria commonly used in auditory brainstem response audiometry (ABR) was analyzed: the interaural V latency difference (ILD V) and the interaural difference of I-V interpeak interval (ID I-V). The distribution of both criteria was Gaussian. By evaluating their standard deviations the percentages of statistical false-positives were estimated. The estimated results were 24% false-positive findings using the decision criterion ILD V greater than 0.2 ms and 5.4% false-positive findings using ID I-V greater than 0.3 ms. This corresponds closely to the actual false-positive ABR rates obtained in this sample: 21.5% and 6.3%, respectively. In a separate series of 301 unselected cases with asymmetric sensorineural hearing loss, 29 ABRs were suspect for retrocochlear pathology. In 20 patients, ABRs were absent due to severe hearing loss. Retrocochlear pathology could be confirmed in only 2 cases (both from the group with ABR present). Thus, 47 ABRs (15.7% of 299) were false-positive.

Cochlear and neural dysfunction in acoustic neuroma: can they be separately revealed by auditory brain-stem wave V latency?

Cochlear and retrocochlear lesions may be differentiated by a diagnostic index (D5), which is derived from the patient's auditory brain-stem wave V latency and pure-tone hearing threshold at 2 to 4 kHz. The D5 values obtained from 49 cases of acoustic neuroma (AN) have been shown to share some properties with D5 values of patients with cochlear hearing loss (280 cases), indicating a lesser prolongation of wave V latency in cases with pronounced hearing loss. Assuming this finding is indicative of some degree of cochlear impairment concomitant to the neural dysfunction, AN data were corrected in an attempt to remove the effects of cochlear impairment. The resulting D5 values could reflect the delay in wave V solely due to the neural dysfunction. A significant relationship between these D5 values and tumour size seems to support this hypothesis.

Auditory brainstem responses in noise-induced permanent hearing loss

Fifty-four patients (108 ears) with presumed noise-induced hearing loss, were subjected to tonal and speech audiometry, impedance tests and measurements of auditory brainstem responses (ABR), in order to check for possible retrocochlear involvement. ABR data indicated that latency values of waves I, III and V, as well as III-I, V-III and V-I intervals fell within the normal range in all cases (M +/- 2 SD), even for fast repetition rates (51 stim/s). Poor waveform resolution of early components, particularly of wave I, was found in 12 ears (11.1%) and a total absence of evoked potentials not always related to the hearing loss, occurred in 5 ears (4.6%).

Influences of birthweight upon brainstem maturation as reflected by auditory brainstem response (ABR) evaluation

The authors have studied auditory brainstem responses (ABR) in 49 preterm (Group A) and in 54 fullterm (Group B) newborns, classified according to the birthweight related to conceptional age, in order to verify the influences of this latter parameter upon ABR. In Group A newborns, 4 recording sessions were performed, while only 3 in Group B, to evaluate data obtained at the same extra-uterine age. The obtained data show that birthweight related to conceptional age seems to play a major role on the development of ABR, since no significant differences were detected between preterm and fullterm newborns, provided the birthweight was appropriate for conceptional age (ACA). On the contrary, small for conceptional age (SCA) newborns showed an abnormal ABR pattern at birth, which tended to normalize at the following recording sessions. The authors conclude that birthweight related to conceptional age represents an important factor in the development of auditory brainstem responses and that the audiological diagnosis has to be very cautious in SCA newborns, regardless if they are pre- or fullterm.

Auditory brain-stem response and hearing threshold in cerebellopontine angle tumours

The auditory brain-stem responses (ABR) in 19 patients with confirmed cerebellopontine angle tumours are evaluated in relation to the hearing threshold as obtained by pure-tone audiometry. ABR pathological alterations, in terms of either absence or presence of components, appear to relate to the suprathreshold stimulus intensity and to match the changes which can be observed in subjects with normal hearing, when stimulated at the equivalent suprathreshold intensity. Of the diagnostic indexes considered (I-V interval, IT5, delta V), IT5 and delta V could be evaluated in the largest patient population. They may be used in combination to enhance their sensitivity in retrocochlear lesion detection.