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Significance of auditory brain stem response and gadolinium-enhanced magnetic resonance imaging for idiopathic sudden sensorineural hearing loss
Significance of auditory brain stem response and gadolinium-enhanced magnetic resonance imaging for idiopathic sudden sensorineural hearing loss NICOLASY. BUSABA,MD, and STEVEND. RAUCH,MD, Boston, Massachusetts Previous studies tried to correlate prognosis and response to oral corticosteroids in patients with idiopathic sudden sensorineural hearing loss to such factors as the age of the patient, presence of vertigo, shape of the audiogram, or severity of the hearing loss. However, temporal bone histopathologic evidence shows that idiopathic sudden sensorineural hearing loss may be caused by cochleitis or cochlear nerve neuritis. Herein we report results of a retrospective study of 96 consecutive patients with idiopathic sudden sensorineural hearing loss who were evaluated with auditory brain stem responses and gadolinium-enhanced magnetic resonance imaging. Results of the auditory brain stem response and magnetic resonance imaging were correlated with hearing outcome. Follow-up was available for 65 patients: 14 with abnormal and 51 with normal auditory brain stem responses. The overall rate of hearing recovery or improvement was 65% in the normal auditory brain stem response group compared with 43% in the abnormal auditory brain stem response group (p = 0.07]. Among the 38 patients treated with a tapering course of oral corticosteroids, the recovery or improvement rate was 83% for those with normal auditory brain stem responses and 56% for those with abnormal auditory brain stem responses (p < 0.05]. Of the 27 patients who did not receive steroid therapy, the improvement rate was 41% in those with normal auditory brain stem responses and 20% in those with abnormal auditory brain stem responses (p = 0.09]. Magnetic resonance imaging with gadolinium was obtained on all 14 patients with abnormal auditory brain stem responses but on none with normal auditory brain stem responses. Only I magnetic resonance image of 14 demonstrated an abnormality, showing a high signal intensity in the distal internal auditory canal; this resolved 6 weeks later on a follow-up magnetic resonance image. We conclude that idiopathic sudden sensorineural hearing loss patients with abnormal auditory brain stem responses have poorer hearing prognoses compared with those patients with normal auditory brain stem responses, irrespective of treatment. Idiopathic sudden sensorineural hearing loss patients with abnormal auditory brain stem responses may have cochlear neuritis causing their hearing loss or may have a more extensive involvement of their auditory system, and this "lesion" may have a lower spontaneous recovery rate and less response to therapy. Magnetic resonance imaging with gadolinium may show abnormal signal intensities along the course of the eighth nerve in patients with idiopathic sudden sensorineural hearing loss, but this is infrequent, and its prognostic implications are not clear. [OTOLARYNGOLHEADNECKSURG 1995; 113:271-5.]
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From the Department of Otolaryngology-Head and Neck Surgery, Massachusetts Eye and Ear Infirmary; and the Department of Otology and Laryngology, Harvard Medical School. Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, San Diego, Calif., Sept. 18--21, 1994. Received for publication Oct. 21, 1994; accepted March 10, 1995. Reprint requests: Nicolas Y. BuSaba, MD, Department of Otolaryngology-Head and Neck Surgery, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114. Copyright © 1995 by the American Academy of Otolaryngolo~Head and Neck Surgery Foundation, Inc. 0194-5998/95/$3.00 + 0 23/1/64761
I d i o p a t h i c s u d d e n s e n s o r i n e u r a l h e a r i n g loss ( I S S H L ) is t h e clinical m a n i f e s t a t i o n of a g r o u p of h e t e r o g e n e o u s d i s o r d e r s . S u g g e s t e d causes i n c l u d e viral infections, v a s c u l a r occlusion, a n d i n n e r e a r m e m b r a n e r u p t u r e s . M a n y factors, such as t h e age of t h e p a t i e n t , 1,2 i n t e r v a l b e t w e e n t h e o n s e t of sympt o m s a n d i n i t i a t i o n o f therapy, 3 severity o f t h e h e a r ing loss, 13 p r e s e n c e o f vertigo, 2 r e d u c e d calorics o n e l e c t r o n y s t a g m o g r a p h y , 2,3 d i s c r i m i n a t i o n s c o r @ a n d s h a p e o f t h e a u d i o g r a m , 3 have b e e n c o r r e l a t e d with r e c o v e ~ a n d s t e r o i d r e s p o n s i v e n e s s in I S S H L p a 271
Head
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BUSABA and RAUCH
tients. However, no attempt has been made to classify ISSHL by possible cause or site of involvement or to study their impact on prognosis. Temporal bone histopathologic evidence shows that ISSHL may be caused by cochleitis or cochlear nerve neuritis. 4 Auditory brain stem responses (ABRs) are abnormal in up to 29% of the cases with the presumed diagnosis of viral neuritis, as in Bell's palsy patients. 58 In a study by BuSaba et al., 9 two patients with ISSHL had abnormal ABRs; one patient recovered his hearing, with the ABR reverting to normal on follow-up. Gadolinium DTPA-enhanced magnetic resonance imaging (Gd-MRI) has been found to sometimes show high signal intensity along the course of the seventh and eighth cranial nerves or in the cochlea during the acute stages of Bell's palsy,1° ISSHL, 11 or Ramsay-Hunt syndrome. 12-14The clinical significance of this observation is not known. However, we propose the hypothesis that abnormal ABR and/or abnormal Gd-MRI are signs of cochlear neuritis and represent a more severe process than cochleitis alone. The purpose of our study was to test this hypothesis by classifying patients with the diagnosis of ISSHL as those with cochleitis vs. those with cochlear neuritis on the basis of ABR and Gd-MRI findings and to correlate each class with hearing outcome and steroid responsiveness. METHODS AND MATERIAL
We performed a retrospective study on 96 consecutive patients who Came to our institution with the diagnosis of ISSHL and had ABR and Gd-MRI studies as part of their workup. ISSHL was defined as a greater than 30 dB loss in three or more contiguous frequencies on pure-tone thresholds during a period of less than 3 days without any identifiable cause. Clinical and audiologic information, such as the age of the patient, sex, duration of symptoms, associated vertigo, severity of the hearing loss, and shape of the audiogram, ABR results, MRI findings, and corticosteroids treatment, was reviewed. Adequate follow-up of at least 6 weeks was available for 65 subjects, and those patients comprised our study group. Patients were divided on the basis of the results of their ABR testing and MRI findings. ABR test results were classified as normal or abnormal as reported in the medical record by the audiologist. Judgments of abnormality were based on the analysis of ABR wave latencies, interwave latencies, and interear-interwave latencies, referenced to laboratory normative values, with a p < 0.01 criterion for each measure. The cutoff criteria for I-III, I-V, and
Otolaryngology and Neck Surgery September 1 9 9 5
wave V interear latency differences were 0.41, 0.46, and 0.52 milliseconds, respectively. MRI results were based on the report of the interpreting radiologist for scans done outside our hospital or by reviewing the films with our radiology faculty for those performed at our facility. Hearing outcome, with or without systemic corticosteroid therapy, was studied in both groups. Hearing was considered improved when pure-tone thresholds for two consecutive frequencies (excluding 8 kHz) were lower by more than 10 dB and/or the discrimination score was higher by more than 15% on follow-up audiograms. Statistical analysis by testing for the difference between two proportions with normal approximation was used, and the level of significance was set at p < 0.05. RESULTS
Ninety-six patients came to our institution with the diagnosis of ISSHL during a 2-year period. Their workup included ABR testing and Gd-MRI studies. ABR was abnormal in 25 patients for an incidence of 26%. Adequate clinical data were available for 65 subjects: 14 with abnormal and 51 with normal ABR results. The abnormal ABR group was composed of nine men and five women. The mean age was 43.6 years (range, 22 to 70 years). Nine patients sought treatment within 2 weeks of onset of their symptoms, and five sought treatment after a 2-week interval. Three (21%) patients had associated vertigo. The puretone average (PTA) on audiometric studies was less than 40 dB in two, 40 to 80 dB in eight (57%), and more than 80 dB in the remaining four subjects. The most common ABR abnormality was wave V interear latency (10 of 14) followed by I-V interwave latency (9 of 14). Nine (64%) patients were treated with a 2-week tapering course of oral corticosteroids (Table I). The normal ABR group consisted of 51 patients, 25 men and 26 women. The mean age was 47.1 years (range, 17 to 80 years). Thirty-nine (76%) patients sought treatment within 2 weeks of the onset of their symptoms. Nine (18%) patients reported vertigo. PTA was less than 40 dB in 13, 40 to 80 dB in 36 (71%), and greater than 80 dB in 2 patients. Twentynine (57%) subjects were treated with oral corticosteroids (Table 1). No significant difference h a s been found between normal and abnormal ABR groups with regard to age, duration of symptoms, vertigo, or PTA. The male-to-female ratio showed a difference ofp -- 0.16, with a predominance of men in the abnormal ABR group. On follow-up, hearing improved in 6 (43%) of 14
Otolaryngology Head and Neck Surgery
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Table
BUSABAand RAUCH 273
Number 3
I. Epidemiologic d a t a of patients with ISSHL Characteristics
Sex (M/F) Age (yr) Mean Range Duration of symptoms <2 wk >2 wk Vertigo Present Absent PTA < 40 dB 40-8O dB > 80 dB Steroid therapy Treated Not treated TOTAL
patients with abnormal ABRs compared with 33 (65%) of 51 patients with normal ABRs (p -- 0.07). Among those treated with corticosteroids, 5 (56%) of 9 patients with abnormal ABRs and 24 (83%) of 29 with normal A B R s had hearing improvement (p < 0.05). This statistically significant difference was independent of other variables such as PTA, age of the patient, or presence of vertigo. Of the 27 patients not treated with systemic corticosteroids, the rate of improvement was 20% in those with abnorma1 ABRs compared with 41% in those with normal ABRs (p = 0.09) (Tables 2 and 3). All patients with abnormal ABRs had Gd-MRI studies. Only one of them showed high signal intensity i~ the distal portion of the internal auditory canal (IAC). That enhancement resolved without any steroid therapy by 6 weeks with concomitant hearing improvement on follow-up audiogram. None of the patients with normal ABRs had an MRI scan. The very small number of patients with abnormal MRI scans precluded statistical analysis. DISCUSSION
ISSHL is believed to be the clinical presentation of a group of heterogeneous disorders. Many potential causes have been implicated, including viral infections, vascular occlusion, cochlear membrane breaks, and neurologic disorders. Wilson et al. ~studied the effect of steroid therapy on hearing recovery rate in 119 ISSHL patients who sought treatment within 10 days of onset of their symptoms. They found that patients with mild hearing loss tended to recover regardless of treatment, whereas those with hearing loss greater than 90 dB in all frequencies had no response to corticosteroid
Normal ABR
25/26 47,1 17-80
Abnormal ABR
9/5 43.6 22-70
39 (76%) 12 (24%)
9 (64%) 5 (36%)
9 (18%) 42 (82%)
3 (21%) 11 (79%)
13 36 (71%) 2
2 8 (57%) 4
29 (57%) 22 (43%) 51
9 (64%) 5 (36%) 14
therapy and had a very limited recovery rate. The study identified a zone of moderate hearing loss (40 to 90 dB), in which a 12-day tapering course of prednisone was beneficial, yielding a 78% recovery" rate compared with 38% in the placebo group, Other favorable prognostic factors include age younger than 40 years, normal electronystagmogram at the time of presentation, or the absence of vertigo.2 In studying 166 patients with sudden hearing loss, Mattox and Simmons3 found that the shape of the audiogram had a strong correlation with recovery; those with upward-sloping audiograms had a better outcome. However, these data did not reflect any specific pathophysiologic mechanism of the hearing loss or indicate the possible site of involvement. Temporal bone histopathologic evidence shows that ISSHL may be due to cochleitis or cochlear neuritis. Schuknecht and Donovan4 reported a cochlear neuritis incidence of 25% in 12 temporal bones of patients with sudden hearing loss. Indirect clinical evidence also shows that diseases probably caused by a viral infection may involve the cochlear nerve, as reflected by ABR abnormalities in up to 29% of patients with Bell's palsy.58 In a prospective study by BuSaba et al. 9 of 21 patients with falsepositive ABRs, 2 patients had ISSHL. One of them recovered hearing, and the ABR reverted to normal on follow-up. In our study, 26% of the ISSHL patients had abnormal ABRsl This figure is similar to the percentage of cochlear neuritis (25%) in temporal bones of patients with sudden hearing loss in the Schuknecht and Donovan studyi4 Our normal ABR and abnormal ABR groups were well matched re-
274
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Table 2. Hearing outcome in ISSHLpatients with
Table 3. Hearing outcome in ISSHLpatients with
normal ABR
abnormal ABR
Groups
Improved [%]
Unchanged[%]
Groups
Improved [%]
Unchanged[%]
Treated with steroids Not treated with steroids Overall
83 41
17 59
56 20
44 80
65
35
Treated with steroids Not treated with steroids Overall
43
57
garding patient age, duration of symptoms, presence of vertigo, and severity of hearing loss (Table 1). Thirty-six (71%) of the 51 patients with normal ABRs and PTAs in the 40 to 80 dB range compared with 8 (57%) of 14 with abnormal ABRs (p = 0.16). The percentages of patients with PTAs less than 40 dB in both groups were also comparable (p = 0.2). Patients with normal A B R results had a higher recovery rate than those with abnormal A B R results, but the difference did not achieve statistical significance (p -- 0.07). This difference was more notably seen in the patients treated with corticosteroids: 83% of those with normal ABRs improved vs. 56% with abnormal ABRs (p < 0.05). The 83% recovery rate of patients with ISSHL and normal ABRs treated with oral steroids agrees well with the "moderate" hearing loss group in the Wilson et al. study 1 (78%). ISSHL patients with abnormal ABRs may have cochlear neuritis causing their hearing loss or may have a more extensive involvement of their auditory system; this "lesion" seems to have a lower spontaneous recovery rate and less responsiveness to corticosteroid treatment. In a prospective study by Schwaber et al., 1° 16 of 17 patients with Bell's palsy had contrast enhancement along the course of the facial nerve on GdMRI lasting for more than 4 months. The most commonly involved site was the distal portion of IAC. This enhancement was thought to denote inflammation of the nerve. However, it had no correlation with the severity of facial paralysis or longterm outcome. These data were corroborated in a recent study by Koshsyu et al. ~5Similar findings were also reported in patients with Ramsay-Hunt syndrome. 12-14Enhancement of the eighth cranial nerve and/or the inner ear was also found in patients with Ramsay-Hunt syndrome who had cochleovestibular symptoms. 12'~4 No correlation was found between MRI enhancement and the severity of symptoms or recovery. Mark et al. 1~reviewed the MRI findings in 12 patients with sudden deafness. Nine of the patients were presumed to have a viral cause of their hearing loss. Cochlear enhancement on G d - M R I
was seen in all of those patients. In two cases, the resolution of symptoms 4 to 6 months later correlated with resolution of the enhancement on MRI. In our study, on the other hand, only 1 of 14 patients with ISSHL and abnormal ABR had high signal intensity in the distal IAC on Gd-MRI. The MRI reverted to normal in 6 weeks, which was associated with hearing improvement. Patients with ISSHL and normal ABRs did not have MRI. Because of the small number of ISSHL patients that showed MRI enhancement in our study group, the implications of such finding could not be determined. CONCLUSION
Approximately a fourth of the patients with ISSHL have abnormal ABRs. ISSHL patients with abnormal ABRs seem to have a less favorable hearing outcome compared with those with normal ABRs, irrespective of treatment. This difference becomes statistically significant when responsiveness to corticosteroid therapy is compared. T h e A B R abnormality may reflect cochlear neuritis or a more extensive involvement of the auditory system. High signal intensity along the course of the eighth cranial nerve may be seen on G d - M R I of patients with ISSHL. Such a finding is not common, and its clinical implications are not known. A long-term prospective study is desirable to better understand the prognostic value of the above findings. REFERENCES 1. Wilson WR, Byl FM, Laird N. The efficacy of steroids in the treatment of idiopathic sudden hearing loss. Arch Otolaryngol 1980;106:772-6. 2. Laird N, Wilson WR. Predicting recovery from idiopathic sudden hearing loss. Am J Otolaryngol 1983;4:161-4. 3. Mattox DE, Simmons FB. Natural history of sudden sensorineural hearing loss. Ann Otol 1977;86:463-80. 4. Schuknecht HF, Donovan ED. The pathology of idiopathic sudden sensorineural hearing loss. Am J Otol 1985;7:1-15. 5. Shanon E, Himelfarb MZ, Zikk D. Measurement of auditory brain stem potentials in Bell's palsy. Laryngoscope 1985;95: 206-9. 6. Rosenthal U, Edstrom S, Hanner P, Badr G, Vahlne A.
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7. 8.
9.
10.
11.
Number 3
Auditory brain stem response abnormalities in patients with Bell's palsy. OTOLARYNGOLHEAD NECKSURG 1983;91:412-6. Uri N, Schuchman G, Pratt H. Auditory brain-stem evoked potentials in Bell's palsy. Arch Otolaryngol 1984;110:301-4. Hendrix RA, Melnick W. Auditory brain stem response and audiologic tests in idiopathic facial nerve paralysis. OTOLARYNGOLH E ~ NECZ~SURG 1983;91:686-90. BuSaba NY, Rebeiz EE, Salman SD, Thornton AR, West C. Significance of false-positive auditory brainstem response: a clinical study. Am J Otol 1994;15:233-6. Scgwaber MK, Larson TC, Zealear DL, Creasy J. Gadolinium-enhancedmagnetic resonance imaging in Bell's palsy. Laryngoscope 1990;100:1264-9. Mark AS, Seltzer S, Nelson-Drake J, Chapman JC, Fitzgerald DC, Gulya AJ. Labyrinthine enhancement on gadoliniumenl~anded magnetic resonance imaging in sudden deafness
BUSABA a n d RAUCH
12.
13.
14.
15.
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and vertigo: correlation with audiologic and electronystagmographic studies. Ann Otol Rhinol Laryngol 1992;101:45964. Yanagida M, Ushiro K, Yamashita T, Kumazawa T, Katoh T. Enhanced MRI in patients with Ramsay-Hunt's syndrome. Acta Otolaryngol Suppl (Stockh) 1993;500:58-61. Li J, Xiong L, Jinkins JR. Gadolinium-enhanced MRI in a patient with AIDS and Ramsay-Hunt syndrome. Neuroradiology 1993;35:269-73. Tada Y, Aoyagi M, Tojima H, et al. Gd-DPTA enhanced MRI in Ramsay Hunt syndrome. Acta Otolaryngol Suppl (Stockh) 1994;511:170-4. Kohsyu H, Aoyagi M, Tojima H. Facial nerve enhancement in Gd-MRI in patients with Bell's palsy. Acta Otolaryngol Suppl (Stockh) 1994;511:165-9.
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From the Department of Otolaryngology-Head and Neck Surgery, Massachusetts Eye and Ear Infirmary; and the Department of Otology and Laryngology, Harvard Medical School. Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, San Diego, Calif., Sept. 18--21, 1994. Received for publication Oct. 21, 1994; accepted March 10, 1995. Reprint requests: Nicolas Y. BuSaba, MD, Department of Otolaryngology-Head and Neck Surgery, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114. Copyright © 1995 by the American Academy of Otolaryngolo~Head and Neck Surgery Foundation, Inc. 0194-5998/95/$3.00 + 0 23/1/64761
I d i o p a t h i c s u d d e n s e n s o r i n e u r a l h e a r i n g loss ( I S S H L ) is t h e clinical m a n i f e s t a t i o n of a g r o u p of h e t e r o g e n e o u s d i s o r d e r s . S u g g e s t e d causes i n c l u d e viral infections, v a s c u l a r occlusion, a n d i n n e r e a r m e m b r a n e r u p t u r e s . M a n y factors, such as t h e age of t h e p a t i e n t , 1,2 i n t e r v a l b e t w e e n t h e o n s e t of sympt o m s a n d i n i t i a t i o n o f therapy, 3 severity o f t h e h e a r ing loss, 13 p r e s e n c e o f vertigo, 2 r e d u c e d calorics o n e l e c t r o n y s t a g m o g r a p h y , 2,3 d i s c r i m i n a t i o n s c o r @ a n d s h a p e o f t h e a u d i o g r a m , 3 have b e e n c o r r e l a t e d with r e c o v e ~ a n d s t e r o i d r e s p o n s i v e n e s s in I S S H L p a 271
Head
272
BUSABA and RAUCH
tients. However, no attempt has been made to classify ISSHL by possible cause or site of involvement or to study their impact on prognosis. Temporal bone histopathologic evidence shows that ISSHL may be caused by cochleitis or cochlear nerve neuritis. 4 Auditory brain stem responses (ABRs) are abnormal in up to 29% of the cases with the presumed diagnosis of viral neuritis, as in Bell's palsy patients. 58 In a study by BuSaba et al., 9 two patients with ISSHL had abnormal ABRs; one patient recovered his hearing, with the ABR reverting to normal on follow-up. Gadolinium DTPA-enhanced magnetic resonance imaging (Gd-MRI) has been found to sometimes show high signal intensity along the course of the seventh and eighth cranial nerves or in the cochlea during the acute stages of Bell's palsy,1° ISSHL, 11 or Ramsay-Hunt syndrome. 12-14The clinical significance of this observation is not known. However, we propose the hypothesis that abnormal ABR and/or abnormal Gd-MRI are signs of cochlear neuritis and represent a more severe process than cochleitis alone. The purpose of our study was to test this hypothesis by classifying patients with the diagnosis of ISSHL as those with cochleitis vs. those with cochlear neuritis on the basis of ABR and Gd-MRI findings and to correlate each class with hearing outcome and steroid responsiveness. METHODS AND MATERIAL
We performed a retrospective study on 96 consecutive patients who Came to our institution with the diagnosis of ISSHL and had ABR and Gd-MRI studies as part of their workup. ISSHL was defined as a greater than 30 dB loss in three or more contiguous frequencies on pure-tone thresholds during a period of less than 3 days without any identifiable cause. Clinical and audiologic information, such as the age of the patient, sex, duration of symptoms, associated vertigo, severity of the hearing loss, and shape of the audiogram, ABR results, MRI findings, and corticosteroids treatment, was reviewed. Adequate follow-up of at least 6 weeks was available for 65 subjects, and those patients comprised our study group. Patients were divided on the basis of the results of their ABR testing and MRI findings. ABR test results were classified as normal or abnormal as reported in the medical record by the audiologist. Judgments of abnormality were based on the analysis of ABR wave latencies, interwave latencies, and interear-interwave latencies, referenced to laboratory normative values, with a p < 0.01 criterion for each measure. The cutoff criteria for I-III, I-V, and
Otolaryngology and Neck Surgery September 1 9 9 5
wave V interear latency differences were 0.41, 0.46, and 0.52 milliseconds, respectively. MRI results were based on the report of the interpreting radiologist for scans done outside our hospital or by reviewing the films with our radiology faculty for those performed at our facility. Hearing outcome, with or without systemic corticosteroid therapy, was studied in both groups. Hearing was considered improved when pure-tone thresholds for two consecutive frequencies (excluding 8 kHz) were lower by more than 10 dB and/or the discrimination score was higher by more than 15% on follow-up audiograms. Statistical analysis by testing for the difference between two proportions with normal approximation was used, and the level of significance was set at p < 0.05. RESULTS
Ninety-six patients came to our institution with the diagnosis of ISSHL during a 2-year period. Their workup included ABR testing and Gd-MRI studies. ABR was abnormal in 25 patients for an incidence of 26%. Adequate clinical data were available for 65 subjects: 14 with abnormal and 51 with normal ABR results. The abnormal ABR group was composed of nine men and five women. The mean age was 43.6 years (range, 22 to 70 years). Nine patients sought treatment within 2 weeks of onset of their symptoms, and five sought treatment after a 2-week interval. Three (21%) patients had associated vertigo. The puretone average (PTA) on audiometric studies was less than 40 dB in two, 40 to 80 dB in eight (57%), and more than 80 dB in the remaining four subjects. The most common ABR abnormality was wave V interear latency (10 of 14) followed by I-V interwave latency (9 of 14). Nine (64%) patients were treated with a 2-week tapering course of oral corticosteroids (Table I). The normal ABR group consisted of 51 patients, 25 men and 26 women. The mean age was 47.1 years (range, 17 to 80 years). Thirty-nine (76%) patients sought treatment within 2 weeks of the onset of their symptoms. Nine (18%) patients reported vertigo. PTA was less than 40 dB in 13, 40 to 80 dB in 36 (71%), and greater than 80 dB in 2 patients. Twentynine (57%) subjects were treated with oral corticosteroids (Table 1). No significant difference h a s been found between normal and abnormal ABR groups with regard to age, duration of symptoms, vertigo, or PTA. The male-to-female ratio showed a difference ofp -- 0.16, with a predominance of men in the abnormal ABR group. On follow-up, hearing improved in 6 (43%) of 14
Otolaryngology Head and Neck Surgery
Volume t t 3
Table
BUSABAand RAUCH 273
Number 3
I. Epidemiologic d a t a of patients with ISSHL Characteristics
Sex (M/F) Age (yr) Mean Range Duration of symptoms <2 wk >2 wk Vertigo Present Absent PTA < 40 dB 40-8O dB > 80 dB Steroid therapy Treated Not treated TOTAL
patients with abnormal ABRs compared with 33 (65%) of 51 patients with normal ABRs (p -- 0.07). Among those treated with corticosteroids, 5 (56%) of 9 patients with abnormal ABRs and 24 (83%) of 29 with normal A B R s had hearing improvement (p < 0.05). This statistically significant difference was independent of other variables such as PTA, age of the patient, or presence of vertigo. Of the 27 patients not treated with systemic corticosteroids, the rate of improvement was 20% in those with abnorma1 ABRs compared with 41% in those with normal ABRs (p = 0.09) (Tables 2 and 3). All patients with abnormal ABRs had Gd-MRI studies. Only one of them showed high signal intensity i~ the distal portion of the internal auditory canal (IAC). That enhancement resolved without any steroid therapy by 6 weeks with concomitant hearing improvement on follow-up audiogram. None of the patients with normal ABRs had an MRI scan. The very small number of patients with abnormal MRI scans precluded statistical analysis. DISCUSSION
ISSHL is believed to be the clinical presentation of a group of heterogeneous disorders. Many potential causes have been implicated, including viral infections, vascular occlusion, cochlear membrane breaks, and neurologic disorders. Wilson et al. ~studied the effect of steroid therapy on hearing recovery rate in 119 ISSHL patients who sought treatment within 10 days of onset of their symptoms. They found that patients with mild hearing loss tended to recover regardless of treatment, whereas those with hearing loss greater than 90 dB in all frequencies had no response to corticosteroid
Normal ABR
25/26 47,1 17-80
Abnormal ABR
9/5 43.6 22-70
39 (76%) 12 (24%)
9 (64%) 5 (36%)
9 (18%) 42 (82%)
3 (21%) 11 (79%)
13 36 (71%) 2
2 8 (57%) 4
29 (57%) 22 (43%) 51
9 (64%) 5 (36%) 14
therapy and had a very limited recovery rate. The study identified a zone of moderate hearing loss (40 to 90 dB), in which a 12-day tapering course of prednisone was beneficial, yielding a 78% recovery" rate compared with 38% in the placebo group, Other favorable prognostic factors include age younger than 40 years, normal electronystagmogram at the time of presentation, or the absence of vertigo.2 In studying 166 patients with sudden hearing loss, Mattox and Simmons3 found that the shape of the audiogram had a strong correlation with recovery; those with upward-sloping audiograms had a better outcome. However, these data did not reflect any specific pathophysiologic mechanism of the hearing loss or indicate the possible site of involvement. Temporal bone histopathologic evidence shows that ISSHL may be due to cochleitis or cochlear neuritis. Schuknecht and Donovan4 reported a cochlear neuritis incidence of 25% in 12 temporal bones of patients with sudden hearing loss. Indirect clinical evidence also shows that diseases probably caused by a viral infection may involve the cochlear nerve, as reflected by ABR abnormalities in up to 29% of patients with Bell's palsy.58 In a prospective study by BuSaba et al. 9 of 21 patients with falsepositive ABRs, 2 patients had ISSHL. One of them recovered hearing, and the ABR reverted to normal on follow-up. In our study, 26% of the ISSHL patients had abnormal ABRsl This figure is similar to the percentage of cochlear neuritis (25%) in temporal bones of patients with sudden hearing loss in the Schuknecht and Donovan studyi4 Our normal ABR and abnormal ABR groups were well matched re-
274
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September 1995
Table 2. Hearing outcome in ISSHLpatients with
Table 3. Hearing outcome in ISSHLpatients with
normal ABR
abnormal ABR
Groups
Improved [%]
Unchanged[%]
Groups
Improved [%]
Unchanged[%]
Treated with steroids Not treated with steroids Overall
83 41
17 59
56 20
44 80
65
35
Treated with steroids Not treated with steroids Overall
43
57
garding patient age, duration of symptoms, presence of vertigo, and severity of hearing loss (Table 1). Thirty-six (71%) of the 51 patients with normal ABRs and PTAs in the 40 to 80 dB range compared with 8 (57%) of 14 with abnormal ABRs (p = 0.16). The percentages of patients with PTAs less than 40 dB in both groups were also comparable (p = 0.2). Patients with normal A B R results had a higher recovery rate than those with abnormal A B R results, but the difference did not achieve statistical significance (p -- 0.07). This difference was more notably seen in the patients treated with corticosteroids: 83% of those with normal ABRs improved vs. 56% with abnormal ABRs (p < 0.05). The 83% recovery rate of patients with ISSHL and normal ABRs treated with oral steroids agrees well with the "moderate" hearing loss group in the Wilson et al. study 1 (78%). ISSHL patients with abnormal ABRs may have cochlear neuritis causing their hearing loss or may have a more extensive involvement of their auditory system; this "lesion" seems to have a lower spontaneous recovery rate and less responsiveness to corticosteroid treatment. In a prospective study by Schwaber et al., 1° 16 of 17 patients with Bell's palsy had contrast enhancement along the course of the facial nerve on GdMRI lasting for more than 4 months. The most commonly involved site was the distal portion of IAC. This enhancement was thought to denote inflammation of the nerve. However, it had no correlation with the severity of facial paralysis or longterm outcome. These data were corroborated in a recent study by Koshsyu et al. ~5Similar findings were also reported in patients with Ramsay-Hunt syndrome. 12-14Enhancement of the eighth cranial nerve and/or the inner ear was also found in patients with Ramsay-Hunt syndrome who had cochleovestibular symptoms. 12'~4 No correlation was found between MRI enhancement and the severity of symptoms or recovery. Mark et al. 1~reviewed the MRI findings in 12 patients with sudden deafness. Nine of the patients were presumed to have a viral cause of their hearing loss. Cochlear enhancement on G d - M R I
was seen in all of those patients. In two cases, the resolution of symptoms 4 to 6 months later correlated with resolution of the enhancement on MRI. In our study, on the other hand, only 1 of 14 patients with ISSHL and abnormal ABR had high signal intensity in the distal IAC on Gd-MRI. The MRI reverted to normal in 6 weeks, which was associated with hearing improvement. Patients with ISSHL and normal ABRs did not have MRI. Because of the small number of ISSHL patients that showed MRI enhancement in our study group, the implications of such finding could not be determined. CONCLUSION
Approximately a fourth of the patients with ISSHL have abnormal ABRs. ISSHL patients with abnormal ABRs seem to have a less favorable hearing outcome compared with those with normal ABRs, irrespective of treatment. This difference becomes statistically significant when responsiveness to corticosteroid therapy is compared. T h e A B R abnormality may reflect cochlear neuritis or a more extensive involvement of the auditory system. High signal intensity along the course of the eighth cranial nerve may be seen on G d - M R I of patients with ISSHL. Such a finding is not common, and its clinical implications are not known. A long-term prospective study is desirable to better understand the prognostic value of the above findings. REFERENCES 1. Wilson WR, Byl FM, Laird N. The efficacy of steroids in the treatment of idiopathic sudden hearing loss. Arch Otolaryngol 1980;106:772-6. 2. Laird N, Wilson WR. Predicting recovery from idiopathic sudden hearing loss. Am J Otolaryngol 1983;4:161-4. 3. Mattox DE, Simmons FB. Natural history of sudden sensorineural hearing loss. Ann Otol 1977;86:463-80. 4. Schuknecht HF, Donovan ED. The pathology of idiopathic sudden sensorineural hearing loss. Am J Otol 1985;7:1-15. 5. Shanon E, Himelfarb MZ, Zikk D. Measurement of auditory brain stem potentials in Bell's palsy. Laryngoscope 1985;95: 206-9. 6. Rosenthal U, Edstrom S, Hanner P, Badr G, Vahlne A.
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Auditory brain stem response abnormalities in patients with Bell's palsy. OTOLARYNGOLHEAD NECKSURG 1983;91:412-6. Uri N, Schuchman G, Pratt H. Auditory brain-stem evoked potentials in Bell's palsy. Arch Otolaryngol 1984;110:301-4. Hendrix RA, Melnick W. Auditory brain stem response and audiologic tests in idiopathic facial nerve paralysis. OTOLARYNGOLH E ~ NECZ~SURG 1983;91:686-90. BuSaba NY, Rebeiz EE, Salman SD, Thornton AR, West C. Significance of false-positive auditory brainstem response: a clinical study. Am J Otol 1994;15:233-6. Scgwaber MK, Larson TC, Zealear DL, Creasy J. Gadolinium-enhancedmagnetic resonance imaging in Bell's palsy. Laryngoscope 1990;100:1264-9. Mark AS, Seltzer S, Nelson-Drake J, Chapman JC, Fitzgerald DC, Gulya AJ. Labyrinthine enhancement on gadoliniumenl~anded magnetic resonance imaging in sudden deafness
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and vertigo: correlation with audiologic and electronystagmographic studies. Ann Otol Rhinol Laryngol 1992;101:45964. Yanagida M, Ushiro K, Yamashita T, Kumazawa T, Katoh T. Enhanced MRI in patients with Ramsay-Hunt's syndrome. Acta Otolaryngol Suppl (Stockh) 1993;500:58-61. Li J, Xiong L, Jinkins JR. Gadolinium-enhanced MRI in a patient with AIDS and Ramsay-Hunt syndrome. Neuroradiology 1993;35:269-73. Tada Y, Aoyagi M, Tojima H, et al. Gd-DPTA enhanced MRI in Ramsay Hunt syndrome. Acta Otolaryngol Suppl (Stockh) 1994;511:170-4. Kohsyu H, Aoyagi M, Tojima H. Facial nerve enhancement in Gd-MRI in patients with Bell's palsy. Acta Otolaryngol Suppl (Stockh) 1994;511:165-9.