Analysis of 4 kHz Notch Audiogram as a Sign of Noise Induced Hearing Loss / 대한이비인후과학회지

ABSTRACT

BACKGROUND AND OBJECTIVES: In this study, we tried to study the criteria and characteristics of patients with noise-induced hearing loss by analyzing the pure tone audiogram such as "C5 dip" or "4 kHz notch". SUBJECTS AND METHOD: Out of 553 patients who complained of tinnitus and hearing loss, medical examination by interview, physical examination, hearing test, brain MRI and survey of tinnitus were performed from January 2010 to December 2012, targeting 81 patients who underwent pure tone hearing test. We analyzed the clinical characteristics of 81 patients with the exception of systemic disease or a history of otologic disease, conductive hearing loss, and vestibular schwannomas. Patients consisted of 70 men and 11 women (34 persons on both sides, 31 persons on right side, and 16 persons on left side), with an average of 48.1+/-12.9 years. 4 kHz notch-type sensorineural hearing loss was compared with contralateral hearing. RESULTS: The audiogram of 4 kHz notch was analyzed, and the results were as follows; 0.5 kHz (11.2+/-9.9 dB HL), 1 kHz (13.2+/-9.9 dB HL), 2 kHz (19.4+/-15.4 dB HL), 3 kHz (38.1+/-18.7 dB HL), 4 kHz (49.3+/-16.2 dB HL), 8 kHz (27.2+/-16.2 dB HL). Among all frequencies of 4 kHz notch audiogram, there was no significant hearing loss in 0.5 kHz and 1 kHz, but significant hearing loss was noted in higher frequencies (paired t-test, p>0.05). The contralateral ear showed a ski-slope hearing loss in about half of the patients. CONCLUSION: Remarkable points of the 4 kHz notch audiogram analysis, known as a typical characteristic of noise-induced hearing loss, were as follows; First, there was hearing loss of about 50 dB HL at 4 kHz. Second, the hearing threshold was improved to about 30 dB HL at 8 kHz. Third, the 4 kHz-notch audiogram showed a significant hearing loss in a high-pitched tone of over 2 kHz, but otherwise there were no significant hearing loss observed in 0.5 kHz and 1 kHz. Fourth, even if there were no symptoms, contralateral ear can still show the ski-slope type of hearing loss.