Relationship of Pure Tone Audiometry and Ossicular Discontinuity in Chronic Suppurative Otitis Media

Abstract

Background: Pure tone audiometry is routinely used to determine conductive and sensorineural hearing status. Ossicular discontinuity is usually assessed intra-operatively. If ossicular discontinuity can be predicted by pure tone audiometry, perhaps the operative procedure of choice and prognosis for hearing can also be anticipated.   Objective: To determine the predictive value of preoperative pure tone audiometry on the presence of gross ossicular discontinuity in chronic otitis media.   Methods: Records of 205 patients, 7 to 75 years of age undergoing their first operation for chronic otitis media were reviewed. Preoperative audiograms and operative records for tympanomastoidectomy were evaluated. A total of 162 patients meeting inclusion criteria were included in the study. Likelihood ratios for positive and negative ossicular discontinuity for frequency-specific air-bone gap cut-offs were determined. Multiple logistic regression analysis for pure tone audiometry and operative findings to predict ossicular discontinuity was performed and a model for predicting ossicular discontinuity using logistic regression obtained.   Results and Conclusion: Frequency-specific air bone gap (ABG) cut-off values can predict ossicular discontinuity in chronic suppurative otitis media namely: < 20 dB ABG at 500 Hz predicts absence of ossicular discontinuity while > 50 dB ABG at 500 Hz, >30 dB ABG at 2 KHz, and > 50 dB ABG at 4 KHz best predict the presence of ossicular discontinuity in general. In the absence of cholesteatoma, the air bone gaps of <30 dB at 500 Hz and <20 dB at 1 KHz decrease probability of ossicular discontinuity from 32.97% to 2.54%. Combination of air bone gaps of >50 dB at 500 Hz, >20 dB at 2 KHz and >40 dB at 4 KHz increase the probability of ossicular discontinuity from 32.97% to 85.9%. These findings suggest that ossicular exploration may not be necessary for the former while an evaluation of the ossicular chain may be mandatory for the latter in the setting where cholesteatoma is not present or suspected.             Presence of cholesteatoma, granulation tissue and size of tympanic membrane perforation are important factors to consider in predicting ossicular discontinuity.   Keywords: air bone gap; audiometry, pure tone; ossicular discontinuity; otitis media, suppurative; logistic reg