Discrepancy in type of tympanogram obtained in cases of ossicular discontinuity appears to be related to frequency of probe tone used in the impedance unit. This suspicion was investigated by obtaining three tympanograms on each of ten patients with disruption of the ossicular chain. Each of three tympanograms utilized a different probe frequency: 220, 625, and 800 Hz.
Results show a clear undulating tympanographic pattern for every case when the 800-Hz probe tone was used, in the majority of cases for the 625-Hz tone, and in no case when the 220-Hz tone was employed. To obtain a tympanogram from a patient with ossicular discontinuity that can be easily distinguished from a version of a type A (normal tracing), we recommend using an electroacoustic impedance unit that employs an 800-Hz probe tone.
Lidén G, Harford E, Hallén O. Tympanometry for the Diagnosis of Ossicular Disruption. Arch Otolaryngol. 1974;99(1):23–29. doi:10.1001/archotol.1974.00780030027005
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