ORIGINAL ARTICLE Chronic Conductive Hearing Loss in Adults Effects on the Auditory Brainstem Response and Masking-Level Difference Michael O. Ferguson, MD; Raymond D. Cook, MD; Joseph W. Hall III, PhD; John H. Grose, PhD; Harold C. Pillsbury III, MD Objective: To determine whether chronic conductive Results: When comparing the patients’ diseased ears hearing loss in adults results in changes in the auditory with their healthy ears, significant delays were seen for brainstem response (ABR) similar to those observed in wave V as well as for the I-V and III-V interwave inter- children with histories of otitis media with effusion. vals. For comparison with the control population, sig- nificant prolongations were again seen for wave V and Design: Test of effect of unilateral conductive hearing for the III-V interwave intervals. In addition, reduced loss on adult ABR using age-matched control group and masking-level differences and significant correlations subjects as their own controls. between the masking-level differences and the ABRs, independent of hearing threshold, were noted. Subjects: Twelve adults with a history of unilateral con- ductive ear disease. An age-matched control group of 21 Conclusions: The results suggest that chronic con- adults was also tested. ductive impairment in adults leads to changes in the ABR similar to those observed in children with histo- Methods: The ABR, an electrophysiologic test of audi- ries of otitis media with effusion. As such, these tory brainstem functioning, was used to evaluate pos- changes do not appear to be related to a critical period sible brainstem abnormalities in the impaired listeners. of development. In addition, the masking-level difference, a behavioral test of binaural auditory processing in the brainstem, was used. Arch Otolaryngol Head Neck Surg. 1998;124:678-685 EVERAL investigations1-7 have tent. Whereas Anteby et al1 found abnor- demonstrated that the audi- mally long wave III-V and wave I-V laten- tory brainstem response cies for children with a history of OME, (ABR) often shows abnor- Folsom et al3 noted significant increases malities in children having in the I-III and III-V interwave intervals, Sa history of otitis media with effusion with significant increases in the absolute (OME) and associated hearing loss. The latencies of waves III and V. Similarly, hypothesis underlying these investiga- Gunnarson and Finitzo5 found signifi- tions is that fluctuation of hearing levels cant delays in the absolute latencies of (HLs) during development may result in waves III and V as well as in the I-III and changes in auditory neural structure and I-V interwave intervals when comparing function, particularly if there is a critical controls with children with OME. In ad- period during maturation in which the dition, they noted an abnormality in the central neurophysiologic condition is rela- binaural interaction response in children tively labile.3 with OME. An investigation by Hall and A common finding in these ABR stud- Grose6 also found increases in the I-III and ies of the juvenile population is an in- I-V interwave intervals and significant de- crease in the interwave intervals com- lays in the absolute latencies of waves III From the Division of pared with a control population, despite and V. Chambers2 noted prolongations in Otolaryngology–Head and resolution of effusion and the presence of the I-III interwave interval, but no in- Neck Surgery, University of normal audiometric thresholds at the time crease in either the III-V or I-V intervals. North Carolina School of Medicine, Chapel Hill. Dr Cook of testing. Although findings of altered A general synopsis of these studies is that is now with the Division of brainstem electrophysiologic features have early conductive impairment results in sig- Otolaryngology–Head and been universal among these studies, the nificant increases in the absolute laten- Neck Surgery, Duke University, specific nature of the interwave changes cies of wave III or V (or both) and 1 or Durham, NC. reported have been somewhat inconsis- more of the interwave intervals. ARCH OTOLARYNGOL HEAD NECK SURG/ VOL 124, JUNE 1998 678 ©1998 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/25/2021 SUBJECTS AND METHODS hearing impairment was about 14 years (range, 2-25 years). None of the patients acquired the hearing loss prior to 12 years of age. SUBJECTS ABR STIMULI AND PROCEDURE Control Group Audiological testing took place in a single-walled sound The control group consisted of 21 adults (10 women and 11 suite. Otoscopic examination was performed by 1 of 2 in- men) ranging in age from 24 to 50 years (mean age, 31.4 years). vestigators (M.O.F. and R.D.C.). The ABR evaluation was Use of the adults as subjects was approved by the human sub- conducted in a quiet examination room after the proce- ject institutional review board. Adults older than 51 years were dures were fully explained and signed consents were ob- excluded from the study because of the possible changes in tained. Subjects were awake and encouraged to relax with the ABR secondary to the degenerative effects of age on the their eyes closed. They were tested in the prone position auditory system.23 Control subjects had no history of hear- in a comfortable reclining chair. The ABR evaluation was ing impairment, ear trauma, or ear surgery. Inclusion in the performed using a Nicolet Spirit evoked potential system control group required that an audiogram with normal results (Nicolet, Madison, Wis). Electroencephalographic activ- be obtained at the time of ABR data collection. ity was recorded for each ear by a midline forehead (non- inverting) electrode (Cz) and an ipsilateral ear canal (in- Experimental Group verting) electrode (A1 or A2), with a ground electrode placed 1 to 2 cm above the nasion. Nicolet gold foil TIPtrodes were This group was composed of 12 adults (10 women and 2 used in the ear canal since it was determined that they op- men) ranging in age from 19 to 49 years (mean age, 37.3 timized the recording of wave I amplitudes, otherwise sil- years). The subjects were drawn either from a list of pa- ver electroencephalographic electrodes were used.24 Inter- tients with conductive hearing impairment scheduled to electrode impedance was maintained at 5000 V or less. undergo corrective middle ear surgery or from conduc- Click stimuli were produced via 100-micosecond rect- tively impaired patients seen for a routine visit in the out- angular electrical pulses transduced through tube phones patient clinic. The cause of impairment was varied, includ- (ER-3A tube phones, Etymotic Research, Elk Grove Vil- ing otosclerosis, cholesteatoma, tympanic membrane lage, Ill). Insert earphones were deeply inserted to obtain perforation, and chronic infection. Inclusion in the experi- maximal interaural attenuation.25-27 Clicks had peak en- mental group required a unilateral chronic conductive hear- ergy at 3000 Hz. Each ear in the control group was stimu- ing loss between 25 and 55 dB HL at 2000 Hz and 4000 lated at click intensity levels of 60, 70, and 90 dB nHL. The Hz, confirmed by repeated audiograms at the time of the diseased ears in the patient group were additionally stimu- study. Individual patient audiograms (air conduction) are lated at 100 dB nHL, and the healthy ears in this group were shown in Table 1. Bone conduction thresholds were always 15 dB HL or better. Average length of time for Continued on next page Animal research has provided additional support brainstem in children with recurrent OME.6,13-15 These for an association between attenuated auditory input studies have shown that the MLD is typically reduced and abnormalities in the auditory brainstem develop- when OME is present, remains significantly decreased ment. Experimentally induced conductive hearing even after the placement of tympanostomy tubes and the impairments during critical periods are known to pro- subsequent return of normal bilateral pure tone audio- duce neural alterations central to the cochlea. Specific metric thresholds in quiet (ie, no noise present),13 but studies have demonstrated abnormalities in the devel- often returns to normal 1 to 2 years following restora- opment of binaural neural elements in the auditory tion of normal hearing thresholds.16 Further study6 ex- brainstem, especially in cases of unilaterally induced amining both MLDs and ABRs in children having a his- conductive hearing loss.8-11 tory of OME with hearing loss showed both reduced MLDs In addition to the use of the ABR as a means of evalu- and abnormalities in the ABRs. In addition, the study ating auditory brainstem function, behavioral evidence showed a significant correlation between the decreased of abnormalities in the brainstem auditory processing can MLDs and the degree of ABR waveform asymmetry. Al- be obtained through the use of the masking-level differ- though the MLD is based on low-frequency stimulation ence (MLD).12 The MLD is a psychoacoustic test that mea- and the ABR is based primarily on high-frequency stimu- sures the sensitivity of the auditory system to interaural lation, both rely critically on brainstem function, and pre- differences of time and amplitude. In the basic configu- vious studies17,18 of listeners with presumed brainstem ration, the masking noise is presented in phase to the 2 pathologic features have shown a significant relation be- ears (No). The signal is presented either in phase to the tween ABR and MLD results. 2 ears (So) or p radians out of phase at the 2 ears (Sp). Interestingly, studies19-22 of adults with acquired con- The MLD is the difference in the levels of the signal at ductive hearing impairment have also indicated re- masked threshold in these 2 configurations.