Otosclerosis (stapes fixation)

Type AsReflex: absentDecay: n/aAir–bone gap: Conductive, with Carhart notch

A shallow (type As) peak at normal pressure. Reflexes are often absent; early disease may show a biphasic on–off pattern.

Audiogram & tympanogram

Audiogram

0204060801001202505001k2k4k8kFrequency (Hz)Hearing level (dB HL)[[[[[[○ air conduction[ bone conduction

Tympanogram

-400-300-200-10001002000.00.51.01.52.02.53.0Ear-canal pressure (daPa)Admittance (mmho)

Reading the two together

Loss type: conductiveMean air-bone gap: 23 dBAir PTA: 40 dB HLDegree: mildCarhart notch: ~13 dB at 2 kHz

An air-bone gap with normal bone thresholds — the lesion is in the outer or middle ear.

An upsloping conductive loss — worst in the low frequencies — with the classic Carhart notch: a bone-conduction dip maximal at 2 kHz. The notch is a mechanical artefact of stapes fixation, not a true cochlear loss, and often resolves after stapes surgery.

The audiogram tells you how much hearing is lost and where the lesion sits (conductive vs sensorineural); the tympanogram tells you what the middle ear is doing mechanically. Read as a pair, they pin down the diagnosis far more tightly than either does alone.

Teaching point

Otosclerosis can produce a marked conductive loss with a near-normal-looking tympanogram — the absent acoustic reflex is often the more sensitive sign.

References

  • Jerger J (1970). Clinical experience with impedance audiometry. Archives of Otolaryngology, 92(4), 311–324.
  • Hunter LL, Shahnaz N (2013). Acoustic Immittance Measures: Basic and Advanced Practice. Plural Publishing.
  • Carhart R (1950). Clinical application of bone conduction audiometry. Archives of Otolaryngology, 51(6), 798–808.