Study Of Auditory Characteristics And Diagnosis Of Acute Low-frequency Sensorineural Hearing Loss

ObjectiveTo analyze the characteristic of pure-tone auditory threshold, measurement of acoustic immittance, auditory brainstem response(ABR), distortion product otoacou-stic emission(DPOAE) and electrocochleogram(ECochG) of acute low-frequency sensorineural hearing loss(ALHL) patients. Investigate the clinical features, audiological symptoms, etiology, pathogenesy and diagnosis of acute low-frequency sensorineural hearing loss.Methods46 patients (47 ears) with a diagnosis of ALHL in ENT department of the first central hospital from September 2007 to July 2009 were involved in the study.20 normal-hearing volunteers (40 ears) were taken in the control group.8 patients (9 ears) with Meniere's disease,7 patients (14 ears) with AN and 18 patients with Sensorineural hearing loss were also selected for this study. Detailed history collection, otological examination, CT/MRI examination and systematic audiological evaluations were conducted. The hearing tests included pure tone audiometry, acoustic immittance, ABR, DPOAE and ECochG. To analyze every examination results, summarize the audiological character of ALHL. All dates were analyzed with statistic method by the software SPSS for Windows Ver 16.0.Results1. Clinical manifestations:46 ALHL patients (47 ears) have low-frequency sensorineural hearing loss of acute onset with unknown cause. The age of the patients were from 16 to 59 years with average on (39.13±11.01) years. Male patients accounted for 16 cases (34.78%) while female for 30 cases (65.22%). Among them,97.83% had unilateral hearing loss and only 2.17% had a bilateral hearing loss.82.98% had low frequency tinnitus, sensation of fullness or occlusion.2. Audiological results2.1 PTT:The average pure tone threshold (APTT) from 0.125 to 1 kHz was (35.00±8.30) dB HL, and (13.62±3.53) dB HL 2 to 8 kHz. Statistical significant differences(P<0.01) of APTT were detected between the ill ears and the healthy ears of ALHL.There also statistical significant differences(P<0.01) between the ill ears of ALHL and the ears of the normal-hearing volunteers at 0.125kHz,0.25kHz,0.5kHz and 1kHz.2.2 Acoustic immitance:All ALHL patients'tympanograms were type "A". Tympanum pressure and static compliance were normal. At 0.5kHz,74.47% of the ill ears acoustic stapedial reflexes were elicited and 65.96% of them had positive results on the Metz test. At 1kHz,82.98% of the ill ears acoustic stapedial reflexes were elicited and 14.89% of them had positive results on the Metz test.2.3 ABR:The responses of ABR were normal in all 47 tested ears of ALHL.2.4 DPOAE:For all the cases of ALHL, DPOAE passed accounted for 19.15% at 0.553-1.105 kHz,90.23% at 2.211-8.837 kHz. Statistical significant differences(P<0.01) of DP-gram were discovered between the ill ears of ALHL and the ears of the normal-hearing volunteers at 0.553kHz,0.783kHz,1.105kHz and 2.211kHz.2.5 ECochG:Statistical significant differences(P<0.01) were found between the ill ears and the healthy ears of ALHL, the ill ears of ALHL and the ears of the normal-hearing volunteers in both-SP amplitude(P<0.01) and-SP/AP(P<0.01). In the 47 ill ears, there were-SP amplitude abnormal increasing in 24 ears (51.06%),-SP/AP ratio abnormal increasing in 30 ears (63.83%).Conclusions1. ALHL patients are clinically characterized by acute onset, mainly unilateral and accompanied by low frequency tinnitus, sensation of fullness or occlusion, female preponderance, with peak incidence during the fourth decade of life.2. ALHL patients'tympanograms were type "A". Tympanum pressure and static compliance were normal which indicated that the function of auris media was normal. The normal ABR showed that the transmission of the auditory neuropathy was complete.3. The hearing loss of ALHL is usually at low frequency suggested that low frequency region cochlear impairment. The positive results on the Metz test showed that the cochlear were affected. The descent of DP-gram at 0.553～1.105kHz revealed the damage of the cochlear apical turn OHCs'function. About 2/3 ALHL patients'ECochG showed abnormal increase in-SP and-SP/AP ratio, characterized by endolymphatic hydrops. These results suggest that ALHL may be caused by endolymphatic hydrops confined to the cochlea apical turn and had specified clinical features.4. The diagnostic criteria of ALHL should be that the average pure tone threshold (APTT) at low-frequency(0.125～1kHz) exceed 26 dB HL. So we can have higher rates of diagnosis.