A 35-year-old man presents with a 10-year history of chronic ear discharge that is scanty, foul-smelling, and occasionally blood-stained. Otoscopy reveals an attic perforation with white pearly debris and granulation tissue. Audiometry shows the pattern marked **B** in the diagram. CT temporal bone confirms erosion of the long process of incus and a labyrinthine fistula. Which of the following BEST explains the hearing loss pattern marked **B**?
A. Sensorineural loss alone from chronic suppuration, with normal air-bone gap
B. Mixed loss: conductive component from ossicular chain disruption plus sensorineural component from labyrinthine inflammation and toxin penetration through the round window
C. Conductive loss alone from ossicular erosion, with normal bone conduction thresholds
D. Progressive conductive loss from Eustachian tube dysfunction without ossicular involvement
Explanation
Why option 2 is correct
The pattern marked B represents MIXED HEARING LOSS, which is the hallmark audiometric finding in CSOM with cholesteatoma. The conductive component arises from progressive destruction of the ossicular chain—most commonly erosion of the long process of incus—due to pressure necrosis and osteolytic enzymes secreted by the keratinizing squamous epithelium. The sensorineural component results from labyrinthine inflammation, penetration of bacterial toxins through the round window membrane, and in this case, direct labyrinthine fistula formation (confirmed on CT). This dual mechanism—ossicular damage plus inner ear involvement—produces the characteristic mixed loss with a persistent air-bone gap and elevated bone conduction thresholds. [Dhingra ENT 8e; Scott-Brown's Otorhinolaryngology 8e]
Why each distractor is wrong
Option 1 (Conductive loss alone): While ossicular erosion does cause a conductive component, it does NOT account for the sensorineural elevation seen in cholesteatoma. The presence of a labyrinthine fistula and chronic suppuration causes additional inner ear damage, raising bone conduction thresholds—this is NOT pure conductive loss.
Option 3 (Sensorineural loss alone): This pattern would show a normal air-bone gap. In cholesteatoma, the air-bone gap is LARGE because of ossicular chain destruction; bone conduction is also elevated due to labyrinthine involvement. Pure sensorineural loss does not fit this clinical picture.
Option 4 (Progressive conductive loss from Eustachian tube dysfunction): While Eustachian tube dysfunction initiates the retraction pocket that leads to cholesteatoma, the hearing loss in established disease is NOT simple conductive loss from tube dysfunction alone. The ossicular erosion and labyrinthine fistula drive the mixed pattern, not tube dysfunction.
