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Asymmetric sensorineural hearing loss in a community-based population
Asymmetric sensorineural hearing loss in a communitybased population SUSAN L. URBEN, MD, MICHAEL S. BENNINGER, MD, and NOREEN D. GIBBENS, MS, Detroit, Michigan
Asymmetric sensorineural hearing loss (ASNHL) is fairly common, but it can be an indication of retrocochlear pathology. The incidence of acoustic neuroma (AN) has been estimated at 1/100,000; however, the incidence of AN in patients with ASNHL is unknown. The limitation of health care resources challenges otolaryngologists to develop reasonable cost-containment guidelines for the evaluation of patients with ASNHL for the presence of retrocochlear pathology. A 5-year (1990 to 1994) retrospective study of all patients with ASNHL who were evaluated in a community-based general otolaryngology practice was performed. Demographic, historic, and audiologic data and results from ABRs and radiologic studies were summarized. ASNHL was present in 325 patients. Auditory brain stem response tests were performed in 179 patients (55%), and 92% (164 of 179) were normal. Patients with abnormal or inconclusive auditory brain stem responses and patients with severe SNHL were evaluated with radiologic studies (46 patients). Among the 193 patients who had diagnostic studies, 4 were found to have ANs, for a prevalence of 2.1%. The charge of diagnosis per AN was more than $41,000. In summary, a small percentage of patients with ASNHL have retrocochlear pathology, and the charge of diagnosis per AN can be excessive. A cost-containment approach for the evaluation and management of patients with ASNHL is proposed. (Otolaryngol Head Neck Surg 1999;120:808-14.)
Asymmetric sensorineural hearing loss (ASNHL) is fairly common, but it can be an early indication of retrocochlear pathology. The incidence of acoustic neuroma
(AN) has been estimated at 1 in 100,000 in the general population1; however, the incidence of AN in patients with ASNHL remains unknown. The limitation of health care resources challenges otolaryngologists to develop reasonable cost-containment guidelines for the evaluation of patients with ASNHL for the presence of retrocochlear pathology. Gadolinium-enhanced MRI scanning of the temporal bones has become the gold standard for the diagnosis of AN, and MRIs are capable of demonstrating more than 99% of tumors and tumors as small as 3 mm.1-7 An alternative screening method is the auditory brain stem response (ABR), which has a reported sensitivity of at least 90% in detecting the presence of retrocochlear pathology.1-10 Although several recent studies have reported that the false-negative rate of the ABR increases with small intracanalicular ANs, these were retrospective studies of patients known to have AN.2,3,8 The sensitivity and predictive value of the ABR increases with the size of the AN.3,4,8,9 Early diagnosis of AN is important because hearing can often be preserved with resection of tumors smaller than 2 cm.2-4 Because ABR testing is considerably less expensive than MRI scanning, ABR testing may continue to be a useful screening method to check for the presence of retrocochlear pathology. The goals of this study were to evaluate the characteristics associated with ASNHL and the prevalence of abnormal ABRs, abnormal radiologic studies, and AN in a community-based population of patients with ASNHL. With this information, a cost-containment approach for the evaluation and management of the patient with ASNHL who seeks treatment from the general otolaryngologist is proposed. METHODS
Department of Otolaryngology–Head and Neck Surgery, Henry Ford Health System. Presented at the Annual Meeting of the American Academy of Otolaryngology–Head and Neck Surgery, San Francisco, CA, September 7-10, 1997. Reprint requests: Michael S. Benninger, MD, Chairman, Department of Otolaryngology–Head and Neck Surgery, Henry Ford Health System, 2799 W Grand Blvd, Detroit, MI 48202-2689. Copyright © 1999 by the American Academy of Otolaryngology– Head and Neck Surgery Foundation, Inc. 0194-5998/99/$8.00 + 0 23/1/92771
A 5-year (January 1, 1990, through December 31, 1994) retrospective study of all patients older than 17 years with ASNHL who were evaluated in a community-based general otolaryngology practice of the Henry Ford Health System in Sterling Heights, MI, was performed. No diagnostic coding is available for ASNHL; therefore patients were identified for inclusion by review of all audiograms performed during the study period. The definition of ASNHL varies among different studies in the literature. In this study and several others, ASNHL is 809
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Table 1. Characteristics of patients with ASNHL Characteristics
Data
Patients with ASNHL Age (y) Median Mean Sex Male Female Ear with greater hearing loss Right Left Hearing loss at presentation* Duration of hearing loss (y) Median Mean History Subjective tinnitus† Vertigo Noise exposure Family history of hearing loss Head or ear trauma Ear surgery Ototoxin exposure
325 51 51.3 ± 13.2 66% (214/324) 34% (110/324) 47% (152/325) 53% (173/325) 73% (222/303) 1 4.6 ± 8.4 65% (188/291) 26% (70/267) 73% (169/232) 41% (31/75) 27% (16/60) 16% (22/32) 30% (3/10)
*Most
patients did not discriminate between the presence of asymmetric or generalized hearing loss. †Most patients did not distinguish between unilateral and bilateral tinnitus.
Table 2. Audiologic characteristics of patients with ASNHL Characteristics
Data
Low-frequency hearing loss Mid-frequency hearing loss High-frequency hearing loss SRT (dB) Median Mean Interaural difference SDS Median Mean Interaural difference Pure-tone threshold dB Gap (dB) Median Mean
29% (95/323) 72% (231/323) 85% (275/323) 15 21.7 ± 19.6 9.9 ± 15.1 92% 83.3% ± 22.2% 9.5% ± 19.0 20 23.4 ± 15.8
gram for public health (Epi Info, version 6, 1995; Division of Surveillance and Epidemiology at the Centers for Disease Control and Prevention, Atlanta, GA, in collaboration with the World Health Organization, Geneva, Switzerland). Appropriate biostatistical measures were performed with Epi Info and were confirmed by a biostatistician. RESULTS
defined as an interaural difference in pure-tone thresholds ≥10 dB at 2 frequencies or ≥15 dB at 1 frequency.5,6 This strict criterion was used by the audiologists and otolaryngologists in this practice during the study period to refer patients with ASNHL for ABR testing to screen for the presence of retrocochlear pathology. All patients’ medical records and audiograms were reviewed for demographic, historic, and audiologic data and results from ABRs and radiologic studies. Audiograms were assessed for the presence of asymmetric low-, mid-, or highfrequency hearing loss. For the purposes of this study, low frequency is defined as ≤750 Hz, mid-frequency is defined as >750 through ≤3000 Hz, and high frequency is defined as > 3000 Hz. The speech reception threshold (SRT), the speech discrimination score (SDS), and the average interaural puretone threshold decibel difference (dB gap) were recorded. The interaural differences in SRT and SDS were also noted. Patients’ subsequent audiograms were compared with the baseline audiogram for the same information, and any progression, stability, or improvement of the patients’ ASNHL was noted. An abnormal ABR was defined as the presence of a wave I-V interpeak latency greater than or equal to 4.4 msec, a wave V interaural latency difference greater than or equal to 0.4 msec, or a poor wave V morphology despite adequate hearing. All radiologic studies were performed in the Henry Ford Health System and were reviewed by a neuroradiologist. All data were entered into a database and statistics pro-
We reviewed 1534 audiograms; 325 adult patients (21%) met the audiologic criteria for ASNHL, and all patients were enrolled in the study. The frequency of ASNHL in all patients who had an audiogram was 21%. Population numbers were not available; therefore the prevalence of ASNHL in this general otolaryngology patient population was not determined. Patient characteristics are summarized in Table 1. Historic information was available for most patients and is shown in Table 1. Historic data about head or ear trauma, ear surgery, family history of hearing loss, ear infections, or ototoxin exposure were less complete, and no significant trends were apparent. Audiologic characteristics are summarized in Table 2. The right and left ears were affected with nearly equal frequency within the low-, mid-, and high-frequency ASNHL groups. Patients were more likely to have simultaneous mid- and high-frequency asymmetry than any other combination. Only 30% (97 of 325) of patients had follow-up audiograms. Audiograms were generally performed at least 1 year after the baseline audiogram. Among these patients, 67% had stable or improved hearing (65 of 97), and 33% (32 of 97) of patients had progressive ASNHL. Only 34 patients had a third audiogram, and 70% of these demonstrated stability or improvement in comparison with the baseline audiogram.
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Table 3. Results of diagnostic studies
811
Table 4. Summary of charges for diagnostic studies
Study
Normal
Abnormal
Total
Study
Number
ABR MRI CT
164 30 19
15 4 0
179 34 19
ABR MRI with Gd CT
179 34 19
TOTAL
Among the 325 patients identified with ASNHL, 193 patients (59%) had diagnostic studies (Table 3). Patients with abnormal or inconclusive ABRs (15 patients) and patients with hearing loss exceeding 60 dB at 3 or 4 kHz were evaluated with radiologic studies. This included 34 gadolinium-enhanced MRIs of the temporal bones and 19 temporal bone CTs with intravenous contrast (46 patients). Four gadolinium-enhanced MRIs of the temporal bones demonstrated retrocochlear pathology. All 4 patients were found to have an AN at surgical resection. If only those patients who had diagnostic studies are considered, the prevalence of AN among patients with ASNHL is 2.1% (4 of 193). Among the 4 patients with ASNHL and AN, half were women, and half were on the left side. The patient’s ages ranged from 29 to 68 years. At presentation, 3 patients had hearing loss (duration range 2 to 30 years). Vertigo, subjective tinnitus, and ASNHL at all frequencies were present in 3 patients each. All 4 patients had low-frequency ASNHL. The interaural dB gap ranged from 10 to 90 dB. SDSs ranged from 0% to 92%. ABRs were done in 3 patients, and all were abnormal. One patient with neurofibromatosis type 2 initially had a temporal bone CT with intravenous contrast that was interpreted as normal. All 4 patients had abnormal findings on gadolinium-enhanced MRIs of the temporal bones. A cost analysis of the evaluation of ASNHL was performed. To assess the cost of diagnosis per AN, we determined the charges for diagnostic studies. Charges may differ from patient costs. Because audiograms were used in the inclusion criteria for the study, the charge for audiograms was excluded. The charges for diagnostic studies were multiplied by the number of studies performed, and a charge of $166,955 was incurred in identifying 4 patients with AN and ASNHL (Table 4). The charge of diagnosis per AN was more than $41,000 ($166,955/4 = $41,738). Of note, more than 8 ABRs can be done for the charge of 1 gadolinium-enhanced MRI of the temporal bones. COST-CONTAINMENT PROPOSAL
Some institutions perform ABRs and/or MRIs in all patients with ASNHL. If all patients in this study had
Charge
× × ×
305 2595 1270
Total
= = =
$54,595 $88,230 $24,130 $166,955
both an ABR and an MRI, the charge of diagnosis per AN would be as high as $128,000, given a prevalence of 2.1%. It would become more reasonable to perform MRIs on patients with ASNHL if the charge for an MRI is reduced to approximate the charge for an ABR. To address the issue of when it is reasonable to perform an ABR or an MRI in patients with ASNHL, we propose a cost-containment approach for the evaluation and management of patients with ASNHL (Fig 1). This approach was developed after review of the information obtained in this study, the experience of our otolaryngologists, and the literature.1-10 It represents a general set of guidelines that have not been validated by this study. For these guidelines to be effective, patients with ASNHL should be evaluated by both otolaryngology and audiology and should have long-term follow-up. It is imperative to evaluate and treat each patient on an individual basis. It is important to take into consideration patient preference, other medical problems, the likelihood of intervention if an AN is diagnosed, and the likelihood of reliable patient follow-up in determining the best clinical approach to each patient. When a patient has a known cause of ASNHL, such as prior ear surgery, trauma, or significant asymmetric noise exposure, and has had no recent changes in his or her hearing, SDSs, or associated symptoms such as subjective tinnitus or vertigo, the recommendation is to repeat an audiogram in 6 months. At that time, if the patient’s hearing, degree of asymmetry, and SDSs are stable or improved in comparison with his or her baseline audiogram, the patient should have annual followup. If the patient’s hearing, degree of asymmetry, or SDSs demonstrate progression or there are other findings that raise the clinical suspicion of the otolaryngologist, the recommendation is to perform an ABR. If the patient has a hearing loss exceeding 60 dB at 3 or 4 kHz, a gadolinium-enhanced MRI of the temporal bones is recommended. When a patient has new-onset ASNHL, progressive ASNHL, or ASNHL of unknown cause, it is important to take into consideration the otolaryngologist’s clinical suspicion for the presence of retrocochlear pathology. If the otolaryngologist has a high clinical suspicion, a gadolinium-enhanced MRI of the temporal bones is rec-
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Fig 1. Proposed cost-containment approach for the evaluation and management of the patient with ASNHL to screen for the presence of retrocochlear pathology.
ommended. If the clinical suspicion is low, an ABR is recommended. If the ABR is normal, the patient should have annual follow-up. If the ABR is abnormal or inconclusive or the patient has a hearing loss exceeding 60 dB at 3 or 4 kHz, a gadolinium-enhanced MRI of the temporal bones is recommended. Patients unable to have an MRI may be evaluated with temporal bone CT with intravenous contrast. If the MRI is normal, the patient should have annual follow-up. If the MRI is abnormal, the patient should be treated according to the pathology. The impact of false-negative ABRs is not known. A small number of patients with AN and ASNHL may not be diagnosed by this cost-containment approach. If there is a high clinical suspicion for the presence of retrocochlear pathology, a definitive study such as a gadolinium-enhanced MRI of the temporal bones should be performed. Additionally, the appropriate duration of follow-up for patients with stable ASNHL
remains undetermined. Until more is understood about the natural history of ASNHL, we encourage long-term evaluation of these patients. DISCUSSION
Within the study population, a cost-containment approach for the evaluation and treatment of patients with ASNHL has been followed by otolaryngologists for several years. The allocation of resources for the evaluation of patients with ASNHL in this study is reasonable. Some institutions and otolaryngologists continue to perform ABRs and/or radiologic studies in all patients with ASNHL. Because AN is rare and ASNHL is commonly seen in otolaryngology and audiology, the cumulative charges for diagnostic studies can be excessive. The guidelines proposed in this study provide the otolaryngologist with a cost-containment approach for the evaluation and treatment of the patient with ASNHL in screening for the presence of retrocochlear pathology.
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Prospective studies using these guidelines are necessary and in progress to determine the accuracy and validity of this approach for the evaluation of patients with ASNHL for the presence of retrocochlear pathology. Although others have proposed algorithms for the evaluation of ASNHL, these have been developed primarily by otolaryngologists with a special interest in otology and retrocochlear pathology. Our approach is unique in that it is based on the experiences of a community-based general otolaryngology practice. Limitations of this study include the retrospective study design, difficulty identifying patients for inclusion in the study, and inconsistencies within the evaluation and management of patients with ASNHL. The creation of a diagnostic code for ASNHL would enable more accurate identification of the incidence and natural history of ASNHL. Inconsistencies in the evaluation and treatment of patients with ASNHL included audiology evaluation without otolaryngology evaluation, variable recommendations for diagnostic studies and follow-up, and patient refusal of diagnostic studies or failure to return for follow-up. An assessment of patients with AN was beyond the scope of this study. A comparison of the cost of diagnosis per AN between this and other studies is difficult because the charges, not the costs, were used in this study. Previous studies, though, have reported a cost of diagnosis per AN ranging from $25987 to $76631 to $18,356.1,7,10 The costs of diagnostic studies, especially that of the MRI, varied widely.1,7 A true cost comparison would require either the patient costs or the charges. The definition of ASNHL varies among different studies in the literature. In this study and several others, ASNHL is defined as an interaural difference in puretone thresholds of ≥10 dB at 2 frequencies or ≥15 dB at 1 frequency.5,6 Another definition of ASNHL is an asymmetry in 2 or more pure-tone thresholds of at least 15 dB or an asymmetry in SDSs of ≥15%.8 A third definition is a pure-tone threshold asymmetry >15 dB at any frequency from 500 to 4000 Hz.7 As more is learned about the natural history of ASNHL, the definition of ASNHL may be modified. Several others have proposed guidelines for the evaluation and treatment of patients with ASNHL. The proposal of Welling et al7 is based on cost-effectiveness and the clinical suspicion of the otolaryngologist. For patients in whom there was a high clinical suspicion for the presence of retrocochlear pathology, an MRI was recommended.7 Abnormal results were treated according to the pathology. Patients with a normal MRI had an ABR, and if the ABR was abnormal, the MRI was repeated. Patients with an intermediate clinical suspicion were also evaluated with an MRI.7 Patients with a
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low clinical suspicion had an ABR, followed by an MRI if the ABR was abnormal. If patients with intermediate and low clinical suspicion had normal results, they were reevaluated.7 Bu-Saba et al5 recommended screening patients with ASNHL with an ABR. Patients with a normal ABR and a low clinical suspicion of retrocochlear pathology were followed up annually. The authors performed an MRI on patients with a high clinical suspicion even if the ABR was normal.5 Patients with abnormal ABRs were evaluated with an imaging study. If the imaging study was normal, annual follow-up with an ABR was recommended with repeat imaging if the ABR remained abnormal.5 Hendrix et al6 also recommended ABR screening of patients with ASNHL. If the ABR was normal, patients were recommended to have a repeat ABR on follow-up in 6 to 12 months.6 If the ABR was abnormal, an MRI was recommended. If the MRI was normal, a repeat MRI in 6 to 12 months was recommended.6 In general, each of these algorithms regards the clinical suspicion of the otolaryngologist and long-term patient follow-up as very important concepts.3,5-7 They generally recommend the ABR as an initial screening method. An MRI is recommended if the ABR is abnormal or the otolaryngologist has a high or intermediate level of clinical suspicion for the presence of retrocochlear pathology.5,7 Repetition of diagnostic studies is common in each of these algorithms. It is unclear, however, whether this is necessary and whether more patients with retrocochlear pathology will be diagnosed with these methods. Mangham10 established a diagnostic cost-effective strategy that would diagnose as many ANs as possible without excessive expenditure. He recommended an MRI for patients with an average difference of ≥20 dB at 1, 2, 4, and 8 kHz and an ABR for patients with a difference of 5 to 20 dB.10 Patients with a high risk (>10%) of an AN should be referred for an MRI. He recognized that some ANs may be missed by this and other cost-effective strategies.10 An MRI is accepted as the gold standard for the detection of retrocochlear pathology1-7,10; however, the cost of this study limits its widespread recommendation. A recent study proposed focused enhanced MRI as a cost-effective alternative.4 This protocol includes pregadolinium- and postgadolinium-enhanced MRI T1weighted images through the internal auditory canal and the region of the cerebellopontine angle, and T2weighted images through the entire brain.4 The total scanning time would be about 12 minutes, and the estimated cost would range from $300 to $500.4 The authors concluded that not only is performance of an MRI less expensive, it is more sensitive and specific, and it limits the need to perform follow-up electrophys-
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iologic and audiometric studies in patients with normal results.4 If focused enhanced MRI were available to most otolaryngologists at a patient cost approximating that of an ABR, it would become more reasonable and cost-effective to perform MRI in patients with ASNHL for whom the otolaryngologist has a high or intermediate clinical suspicion for the presence of retrocochlear pathology. However, until this imaging study is available to more otolaryngologists, we recommend following the costcontainment guidelines proposed herein. CONCLUSION
In summary, ASNHL involves the right and left ears nearly equally. It is often associated with subjective tinnitus and a history of significant noise exposure and less often with vertigo. ASNHL most commonly involves the high frequency followed by the mid-frequency range. ABRs were performed in 55% of patients in this study, and 92% were normal. Only 14% of patients had radiologic studies. AN was an infrequent finding among patients with ASNHL, and the prevalence was 2.1% in this study. The impact of false-negative ABRs is not known, so the actual incidence of AN among patients with ASNHL may be slightly higher than 2.1%. The charge of diagnosis per AN was more than $41,000.
We thank Julie A. Masura, MS, Biostatistics and Research Epidemiology, Henry Ford Hospital, Detroit, for her assistance in data analysis. REFERENCES 1. Kotlarz JP, Eby TL, Borton TE. Analysis of the efficiency of retrocochlear screening. Laryngoscope 1992;102:1108-12. 2. Wilson DF, Hodgson RS, Gustafson MF, et al. The sensitivity of auditory brainstem response testing in small acoustic neuromas. Laryngoscope 1992;102:961-4. 3. Chandrasekhar SS, Brackmann DE, Devgan KK. Utility of auditory brainstem response audiometry in diagnosis of acoustic neuromas. Am J Otol 1995;16:63-7. 4. Carrier DA, Arriaga MA. Cost-effective evaluation of asymmetric sensorineural hearing loss with focused magnetic resonance imaging. Otolaryngol Head Neck Surg 1997;116:567-74. 5. Bu-Saba NY, Reveiz EE, Salman SD, et al. Significance of falsepositive auditory brainstem response: a clinical study. Am J Otol 1994;15:233-6. 6. Hendrix RA, DeDio RM, Sclafani AP. The use of diagnostic testing in asymmetric sensorineural hearing loss. Otolaryngol Head Neck Surg 1990;103:593-8. 7. Welling DB, Glasscock ME, Woods CI, et al. Acoustic neuroma: a cost-effective approach. Otolaryngol Head Neck Surg 1990; 103:364-70. 8. Ruckenstein MJ, Cueva RA, Morrison DH, et al. A prospective study of ABR and MRI in the screening for vestibular schwannomas. Am J Otol 1996;17:317-20. 9. Selters WA, Brackmann DE. Acoustic tumor detection with brain stem electric response audiometry. Arch Otolaryngol 1977;103: 181-7. 10. Mangham CA. Hearing threshold difference between ears and risk of acoustic tumor. Otolaryngol Head Neck Surg 1991;105:814-7.
Management of the Tinnitus Patient
This seventh annual conference, sponsored by the University of Iowa Departments of Otolaryngology–Head and Neck Surgery and Speech Pathology and Audiology, will be held September 30–October 2, 1999, at the University of Iowa Hospitals and Clinics, Iowa City, IA. For further information, contact the Center for Conferences and Institutes, University of Iowa, 249 Iowa Memorial Union, Iowa City, IA 52242-1317; phone, 900-551-9029; fax, 319-335-3533.
Asymmetric sensorineural hearing loss (ASNHL) is fairly common, but it can be an indication of retrocochlear pathology. The incidence of acoustic neuroma (AN) has been estimated at 1/100,000; however, the incidence of AN in patients with ASNHL is unknown. The limitation of health care resources challenges otolaryngologists to develop reasonable cost-containment guidelines for the evaluation of patients with ASNHL for the presence of retrocochlear pathology. A 5-year (1990 to 1994) retrospective study of all patients with ASNHL who were evaluated in a community-based general otolaryngology practice was performed. Demographic, historic, and audiologic data and results from ABRs and radiologic studies were summarized. ASNHL was present in 325 patients. Auditory brain stem response tests were performed in 179 patients (55%), and 92% (164 of 179) were normal. Patients with abnormal or inconclusive auditory brain stem responses and patients with severe SNHL were evaluated with radiologic studies (46 patients). Among the 193 patients who had diagnostic studies, 4 were found to have ANs, for a prevalence of 2.1%. The charge of diagnosis per AN was more than $41,000. In summary, a small percentage of patients with ASNHL have retrocochlear pathology, and the charge of diagnosis per AN can be excessive. A cost-containment approach for the evaluation and management of patients with ASNHL is proposed. (Otolaryngol Head Neck Surg 1999;120:808-14.)
Asymmetric sensorineural hearing loss (ASNHL) is fairly common, but it can be an early indication of retrocochlear pathology. The incidence of acoustic neuroma
(AN) has been estimated at 1 in 100,000 in the general population1; however, the incidence of AN in patients with ASNHL remains unknown. The limitation of health care resources challenges otolaryngologists to develop reasonable cost-containment guidelines for the evaluation of patients with ASNHL for the presence of retrocochlear pathology. Gadolinium-enhanced MRI scanning of the temporal bones has become the gold standard for the diagnosis of AN, and MRIs are capable of demonstrating more than 99% of tumors and tumors as small as 3 mm.1-7 An alternative screening method is the auditory brain stem response (ABR), which has a reported sensitivity of at least 90% in detecting the presence of retrocochlear pathology.1-10 Although several recent studies have reported that the false-negative rate of the ABR increases with small intracanalicular ANs, these were retrospective studies of patients known to have AN.2,3,8 The sensitivity and predictive value of the ABR increases with the size of the AN.3,4,8,9 Early diagnosis of AN is important because hearing can often be preserved with resection of tumors smaller than 2 cm.2-4 Because ABR testing is considerably less expensive than MRI scanning, ABR testing may continue to be a useful screening method to check for the presence of retrocochlear pathology. The goals of this study were to evaluate the characteristics associated with ASNHL and the prevalence of abnormal ABRs, abnormal radiologic studies, and AN in a community-based population of patients with ASNHL. With this information, a cost-containment approach for the evaluation and management of the patient with ASNHL who seeks treatment from the general otolaryngologist is proposed. METHODS
Department of Otolaryngology–Head and Neck Surgery, Henry Ford Health System. Presented at the Annual Meeting of the American Academy of Otolaryngology–Head and Neck Surgery, San Francisco, CA, September 7-10, 1997. Reprint requests: Michael S. Benninger, MD, Chairman, Department of Otolaryngology–Head and Neck Surgery, Henry Ford Health System, 2799 W Grand Blvd, Detroit, MI 48202-2689. Copyright © 1999 by the American Academy of Otolaryngology– Head and Neck Surgery Foundation, Inc. 0194-5998/99/$8.00 + 0 23/1/92771
A 5-year (January 1, 1990, through December 31, 1994) retrospective study of all patients older than 17 years with ASNHL who were evaluated in a community-based general otolaryngology practice of the Henry Ford Health System in Sterling Heights, MI, was performed. No diagnostic coding is available for ASNHL; therefore patients were identified for inclusion by review of all audiograms performed during the study period. The definition of ASNHL varies among different studies in the literature. In this study and several others, ASNHL is 809
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Table 1. Characteristics of patients with ASNHL Characteristics
Data
Patients with ASNHL Age (y) Median Mean Sex Male Female Ear with greater hearing loss Right Left Hearing loss at presentation* Duration of hearing loss (y) Median Mean History Subjective tinnitus† Vertigo Noise exposure Family history of hearing loss Head or ear trauma Ear surgery Ototoxin exposure
325 51 51.3 ± 13.2 66% (214/324) 34% (110/324) 47% (152/325) 53% (173/325) 73% (222/303) 1 4.6 ± 8.4 65% (188/291) 26% (70/267) 73% (169/232) 41% (31/75) 27% (16/60) 16% (22/32) 30% (3/10)
*Most
patients did not discriminate between the presence of asymmetric or generalized hearing loss. †Most patients did not distinguish between unilateral and bilateral tinnitus.
Table 2. Audiologic characteristics of patients with ASNHL Characteristics
Data
Low-frequency hearing loss Mid-frequency hearing loss High-frequency hearing loss SRT (dB) Median Mean Interaural difference SDS Median Mean Interaural difference Pure-tone threshold dB Gap (dB) Median Mean
29% (95/323) 72% (231/323) 85% (275/323) 15 21.7 ± 19.6 9.9 ± 15.1 92% 83.3% ± 22.2% 9.5% ± 19.0 20 23.4 ± 15.8
gram for public health (Epi Info, version 6, 1995; Division of Surveillance and Epidemiology at the Centers for Disease Control and Prevention, Atlanta, GA, in collaboration with the World Health Organization, Geneva, Switzerland). Appropriate biostatistical measures were performed with Epi Info and were confirmed by a biostatistician. RESULTS
defined as an interaural difference in pure-tone thresholds ≥10 dB at 2 frequencies or ≥15 dB at 1 frequency.5,6 This strict criterion was used by the audiologists and otolaryngologists in this practice during the study period to refer patients with ASNHL for ABR testing to screen for the presence of retrocochlear pathology. All patients’ medical records and audiograms were reviewed for demographic, historic, and audiologic data and results from ABRs and radiologic studies. Audiograms were assessed for the presence of asymmetric low-, mid-, or highfrequency hearing loss. For the purposes of this study, low frequency is defined as ≤750 Hz, mid-frequency is defined as >750 through ≤3000 Hz, and high frequency is defined as > 3000 Hz. The speech reception threshold (SRT), the speech discrimination score (SDS), and the average interaural puretone threshold decibel difference (dB gap) were recorded. The interaural differences in SRT and SDS were also noted. Patients’ subsequent audiograms were compared with the baseline audiogram for the same information, and any progression, stability, or improvement of the patients’ ASNHL was noted. An abnormal ABR was defined as the presence of a wave I-V interpeak latency greater than or equal to 4.4 msec, a wave V interaural latency difference greater than or equal to 0.4 msec, or a poor wave V morphology despite adequate hearing. All radiologic studies were performed in the Henry Ford Health System and were reviewed by a neuroradiologist. All data were entered into a database and statistics pro-
We reviewed 1534 audiograms; 325 adult patients (21%) met the audiologic criteria for ASNHL, and all patients were enrolled in the study. The frequency of ASNHL in all patients who had an audiogram was 21%. Population numbers were not available; therefore the prevalence of ASNHL in this general otolaryngology patient population was not determined. Patient characteristics are summarized in Table 1. Historic information was available for most patients and is shown in Table 1. Historic data about head or ear trauma, ear surgery, family history of hearing loss, ear infections, or ototoxin exposure were less complete, and no significant trends were apparent. Audiologic characteristics are summarized in Table 2. The right and left ears were affected with nearly equal frequency within the low-, mid-, and high-frequency ASNHL groups. Patients were more likely to have simultaneous mid- and high-frequency asymmetry than any other combination. Only 30% (97 of 325) of patients had follow-up audiograms. Audiograms were generally performed at least 1 year after the baseline audiogram. Among these patients, 67% had stable or improved hearing (65 of 97), and 33% (32 of 97) of patients had progressive ASNHL. Only 34 patients had a third audiogram, and 70% of these demonstrated stability or improvement in comparison with the baseline audiogram.
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Table 3. Results of diagnostic studies
811
Table 4. Summary of charges for diagnostic studies
Study
Normal
Abnormal
Total
Study
Number
ABR MRI CT
164 30 19
15 4 0
179 34 19
ABR MRI with Gd CT
179 34 19
TOTAL
Among the 325 patients identified with ASNHL, 193 patients (59%) had diagnostic studies (Table 3). Patients with abnormal or inconclusive ABRs (15 patients) and patients with hearing loss exceeding 60 dB at 3 or 4 kHz were evaluated with radiologic studies. This included 34 gadolinium-enhanced MRIs of the temporal bones and 19 temporal bone CTs with intravenous contrast (46 patients). Four gadolinium-enhanced MRIs of the temporal bones demonstrated retrocochlear pathology. All 4 patients were found to have an AN at surgical resection. If only those patients who had diagnostic studies are considered, the prevalence of AN among patients with ASNHL is 2.1% (4 of 193). Among the 4 patients with ASNHL and AN, half were women, and half were on the left side. The patient’s ages ranged from 29 to 68 years. At presentation, 3 patients had hearing loss (duration range 2 to 30 years). Vertigo, subjective tinnitus, and ASNHL at all frequencies were present in 3 patients each. All 4 patients had low-frequency ASNHL. The interaural dB gap ranged from 10 to 90 dB. SDSs ranged from 0% to 92%. ABRs were done in 3 patients, and all were abnormal. One patient with neurofibromatosis type 2 initially had a temporal bone CT with intravenous contrast that was interpreted as normal. All 4 patients had abnormal findings on gadolinium-enhanced MRIs of the temporal bones. A cost analysis of the evaluation of ASNHL was performed. To assess the cost of diagnosis per AN, we determined the charges for diagnostic studies. Charges may differ from patient costs. Because audiograms were used in the inclusion criteria for the study, the charge for audiograms was excluded. The charges for diagnostic studies were multiplied by the number of studies performed, and a charge of $166,955 was incurred in identifying 4 patients with AN and ASNHL (Table 4). The charge of diagnosis per AN was more than $41,000 ($166,955/4 = $41,738). Of note, more than 8 ABRs can be done for the charge of 1 gadolinium-enhanced MRI of the temporal bones. COST-CONTAINMENT PROPOSAL
Some institutions perform ABRs and/or MRIs in all patients with ASNHL. If all patients in this study had
Charge
× × ×
305 2595 1270
Total
= = =
$54,595 $88,230 $24,130 $166,955
both an ABR and an MRI, the charge of diagnosis per AN would be as high as $128,000, given a prevalence of 2.1%. It would become more reasonable to perform MRIs on patients with ASNHL if the charge for an MRI is reduced to approximate the charge for an ABR. To address the issue of when it is reasonable to perform an ABR or an MRI in patients with ASNHL, we propose a cost-containment approach for the evaluation and management of patients with ASNHL (Fig 1). This approach was developed after review of the information obtained in this study, the experience of our otolaryngologists, and the literature.1-10 It represents a general set of guidelines that have not been validated by this study. For these guidelines to be effective, patients with ASNHL should be evaluated by both otolaryngology and audiology and should have long-term follow-up. It is imperative to evaluate and treat each patient on an individual basis. It is important to take into consideration patient preference, other medical problems, the likelihood of intervention if an AN is diagnosed, and the likelihood of reliable patient follow-up in determining the best clinical approach to each patient. When a patient has a known cause of ASNHL, such as prior ear surgery, trauma, or significant asymmetric noise exposure, and has had no recent changes in his or her hearing, SDSs, or associated symptoms such as subjective tinnitus or vertigo, the recommendation is to repeat an audiogram in 6 months. At that time, if the patient’s hearing, degree of asymmetry, and SDSs are stable or improved in comparison with his or her baseline audiogram, the patient should have annual followup. If the patient’s hearing, degree of asymmetry, or SDSs demonstrate progression or there are other findings that raise the clinical suspicion of the otolaryngologist, the recommendation is to perform an ABR. If the patient has a hearing loss exceeding 60 dB at 3 or 4 kHz, a gadolinium-enhanced MRI of the temporal bones is recommended. When a patient has new-onset ASNHL, progressive ASNHL, or ASNHL of unknown cause, it is important to take into consideration the otolaryngologist’s clinical suspicion for the presence of retrocochlear pathology. If the otolaryngologist has a high clinical suspicion, a gadolinium-enhanced MRI of the temporal bones is rec-
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Fig 1. Proposed cost-containment approach for the evaluation and management of the patient with ASNHL to screen for the presence of retrocochlear pathology.
ommended. If the clinical suspicion is low, an ABR is recommended. If the ABR is normal, the patient should have annual follow-up. If the ABR is abnormal or inconclusive or the patient has a hearing loss exceeding 60 dB at 3 or 4 kHz, a gadolinium-enhanced MRI of the temporal bones is recommended. Patients unable to have an MRI may be evaluated with temporal bone CT with intravenous contrast. If the MRI is normal, the patient should have annual follow-up. If the MRI is abnormal, the patient should be treated according to the pathology. The impact of false-negative ABRs is not known. A small number of patients with AN and ASNHL may not be diagnosed by this cost-containment approach. If there is a high clinical suspicion for the presence of retrocochlear pathology, a definitive study such as a gadolinium-enhanced MRI of the temporal bones should be performed. Additionally, the appropriate duration of follow-up for patients with stable ASNHL
remains undetermined. Until more is understood about the natural history of ASNHL, we encourage long-term evaluation of these patients. DISCUSSION
Within the study population, a cost-containment approach for the evaluation and treatment of patients with ASNHL has been followed by otolaryngologists for several years. The allocation of resources for the evaluation of patients with ASNHL in this study is reasonable. Some institutions and otolaryngologists continue to perform ABRs and/or radiologic studies in all patients with ASNHL. Because AN is rare and ASNHL is commonly seen in otolaryngology and audiology, the cumulative charges for diagnostic studies can be excessive. The guidelines proposed in this study provide the otolaryngologist with a cost-containment approach for the evaluation and treatment of the patient with ASNHL in screening for the presence of retrocochlear pathology.
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Prospective studies using these guidelines are necessary and in progress to determine the accuracy and validity of this approach for the evaluation of patients with ASNHL for the presence of retrocochlear pathology. Although others have proposed algorithms for the evaluation of ASNHL, these have been developed primarily by otolaryngologists with a special interest in otology and retrocochlear pathology. Our approach is unique in that it is based on the experiences of a community-based general otolaryngology practice. Limitations of this study include the retrospective study design, difficulty identifying patients for inclusion in the study, and inconsistencies within the evaluation and management of patients with ASNHL. The creation of a diagnostic code for ASNHL would enable more accurate identification of the incidence and natural history of ASNHL. Inconsistencies in the evaluation and treatment of patients with ASNHL included audiology evaluation without otolaryngology evaluation, variable recommendations for diagnostic studies and follow-up, and patient refusal of diagnostic studies or failure to return for follow-up. An assessment of patients with AN was beyond the scope of this study. A comparison of the cost of diagnosis per AN between this and other studies is difficult because the charges, not the costs, were used in this study. Previous studies, though, have reported a cost of diagnosis per AN ranging from $25987 to $76631 to $18,356.1,7,10 The costs of diagnostic studies, especially that of the MRI, varied widely.1,7 A true cost comparison would require either the patient costs or the charges. The definition of ASNHL varies among different studies in the literature. In this study and several others, ASNHL is defined as an interaural difference in puretone thresholds of ≥10 dB at 2 frequencies or ≥15 dB at 1 frequency.5,6 Another definition of ASNHL is an asymmetry in 2 or more pure-tone thresholds of at least 15 dB or an asymmetry in SDSs of ≥15%.8 A third definition is a pure-tone threshold asymmetry >15 dB at any frequency from 500 to 4000 Hz.7 As more is learned about the natural history of ASNHL, the definition of ASNHL may be modified. Several others have proposed guidelines for the evaluation and treatment of patients with ASNHL. The proposal of Welling et al7 is based on cost-effectiveness and the clinical suspicion of the otolaryngologist. For patients in whom there was a high clinical suspicion for the presence of retrocochlear pathology, an MRI was recommended.7 Abnormal results were treated according to the pathology. Patients with a normal MRI had an ABR, and if the ABR was abnormal, the MRI was repeated. Patients with an intermediate clinical suspicion were also evaluated with an MRI.7 Patients with a
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low clinical suspicion had an ABR, followed by an MRI if the ABR was abnormal. If patients with intermediate and low clinical suspicion had normal results, they were reevaluated.7 Bu-Saba et al5 recommended screening patients with ASNHL with an ABR. Patients with a normal ABR and a low clinical suspicion of retrocochlear pathology were followed up annually. The authors performed an MRI on patients with a high clinical suspicion even if the ABR was normal.5 Patients with abnormal ABRs were evaluated with an imaging study. If the imaging study was normal, annual follow-up with an ABR was recommended with repeat imaging if the ABR remained abnormal.5 Hendrix et al6 also recommended ABR screening of patients with ASNHL. If the ABR was normal, patients were recommended to have a repeat ABR on follow-up in 6 to 12 months.6 If the ABR was abnormal, an MRI was recommended. If the MRI was normal, a repeat MRI in 6 to 12 months was recommended.6 In general, each of these algorithms regards the clinical suspicion of the otolaryngologist and long-term patient follow-up as very important concepts.3,5-7 They generally recommend the ABR as an initial screening method. An MRI is recommended if the ABR is abnormal or the otolaryngologist has a high or intermediate level of clinical suspicion for the presence of retrocochlear pathology.5,7 Repetition of diagnostic studies is common in each of these algorithms. It is unclear, however, whether this is necessary and whether more patients with retrocochlear pathology will be diagnosed with these methods. Mangham10 established a diagnostic cost-effective strategy that would diagnose as many ANs as possible without excessive expenditure. He recommended an MRI for patients with an average difference of ≥20 dB at 1, 2, 4, and 8 kHz and an ABR for patients with a difference of 5 to 20 dB.10 Patients with a high risk (>10%) of an AN should be referred for an MRI. He recognized that some ANs may be missed by this and other cost-effective strategies.10 An MRI is accepted as the gold standard for the detection of retrocochlear pathology1-7,10; however, the cost of this study limits its widespread recommendation. A recent study proposed focused enhanced MRI as a cost-effective alternative.4 This protocol includes pregadolinium- and postgadolinium-enhanced MRI T1weighted images through the internal auditory canal and the region of the cerebellopontine angle, and T2weighted images through the entire brain.4 The total scanning time would be about 12 minutes, and the estimated cost would range from $300 to $500.4 The authors concluded that not only is performance of an MRI less expensive, it is more sensitive and specific, and it limits the need to perform follow-up electrophys-
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iologic and audiometric studies in patients with normal results.4 If focused enhanced MRI were available to most otolaryngologists at a patient cost approximating that of an ABR, it would become more reasonable and cost-effective to perform MRI in patients with ASNHL for whom the otolaryngologist has a high or intermediate clinical suspicion for the presence of retrocochlear pathology. However, until this imaging study is available to more otolaryngologists, we recommend following the costcontainment guidelines proposed herein. CONCLUSION
In summary, ASNHL involves the right and left ears nearly equally. It is often associated with subjective tinnitus and a history of significant noise exposure and less often with vertigo. ASNHL most commonly involves the high frequency followed by the mid-frequency range. ABRs were performed in 55% of patients in this study, and 92% were normal. Only 14% of patients had radiologic studies. AN was an infrequent finding among patients with ASNHL, and the prevalence was 2.1% in this study. The impact of false-negative ABRs is not known, so the actual incidence of AN among patients with ASNHL may be slightly higher than 2.1%. The charge of diagnosis per AN was more than $41,000.
We thank Julie A. Masura, MS, Biostatistics and Research Epidemiology, Henry Ford Hospital, Detroit, for her assistance in data analysis. REFERENCES 1. Kotlarz JP, Eby TL, Borton TE. Analysis of the efficiency of retrocochlear screening. Laryngoscope 1992;102:1108-12. 2. Wilson DF, Hodgson RS, Gustafson MF, et al. The sensitivity of auditory brainstem response testing in small acoustic neuromas. Laryngoscope 1992;102:961-4. 3. Chandrasekhar SS, Brackmann DE, Devgan KK. Utility of auditory brainstem response audiometry in diagnosis of acoustic neuromas. Am J Otol 1995;16:63-7. 4. Carrier DA, Arriaga MA. Cost-effective evaluation of asymmetric sensorineural hearing loss with focused magnetic resonance imaging. Otolaryngol Head Neck Surg 1997;116:567-74. 5. Bu-Saba NY, Reveiz EE, Salman SD, et al. Significance of falsepositive auditory brainstem response: a clinical study. Am J Otol 1994;15:233-6. 6. Hendrix RA, DeDio RM, Sclafani AP. The use of diagnostic testing in asymmetric sensorineural hearing loss. Otolaryngol Head Neck Surg 1990;103:593-8. 7. Welling DB, Glasscock ME, Woods CI, et al. Acoustic neuroma: a cost-effective approach. Otolaryngol Head Neck Surg 1990; 103:364-70. 8. Ruckenstein MJ, Cueva RA, Morrison DH, et al. A prospective study of ABR and MRI in the screening for vestibular schwannomas. Am J Otol 1996;17:317-20. 9. Selters WA, Brackmann DE. Acoustic tumor detection with brain stem electric response audiometry. Arch Otolaryngol 1977;103: 181-7. 10. Mangham CA. Hearing threshold difference between ears and risk of acoustic tumor. Otolaryngol Head Neck Surg 1991;105:814-7.
Management of the Tinnitus Patient
This seventh annual conference, sponsored by the University of Iowa Departments of Otolaryngology–Head and Neck Surgery and Speech Pathology and Audiology, will be held September 30–October 2, 1999, at the University of Iowa Hospitals and Clinics, Iowa City, IA. For further information, contact the Center for Conferences and Institutes, University of Iowa, 249 Iowa Memorial Union, Iowa City, IA 52242-1317; phone, 900-551-9029; fax, 319-335-3533.