A 35-year-old man from rural India presents with a 2-year history of intermittent ear discharge and progressive hearing loss. Otoscopy reveals a central tympanic membrane perforation with mucoid discharge. Audiometry shows an air-bone gap of 35 dB at low frequencies with reduced bone conduction thresholds at high frequencies, creating the pattern marked **C** in the diagram. Which of the following best explains the audiological findings in this patient?

Explanation

## Why Mixed hearing loss (option B) is right The pattern marked **C** in the diagram represents a mixed hearing loss pattern — both conductive and sensorineural components. In chronic suppurative otitis media (CSOM), the initial conductive loss results from tympanic membrane perforation and ossicular discontinuity. However, in long-standing disease (>3 months with persistent otorrhea), chronic exposure to bacterial toxins and inflammatory mediators causes cochlear damage, producing a superimposed sensorineural hearing loss. This creates the characteristic mixed audiogram with an air-bone gap AND reduced bone conduction thresholds — exactly the pattern shown at **C**. Dhingra ENT 7e emphasizes that CSOM progresses from pure conductive loss to mixed loss as cochlear involvement develops, and this progression is a key reason for early intervention to prevent irreversible sensorineural damage. ## Why each distractor is wrong - **Conductive hearing loss alone**: This describes only the early phase of CSOM (TM perforation + ossicular damage). The presence of reduced bone conduction thresholds at high frequencies rules out pure conductive loss and indicates sensorineural involvement — the hallmark of the mixed pattern at **C**. - **Sensorineural hearing loss alone**: CSOM primarily causes conductive loss initially. Pure SNHL would show normal air-bone gap and symmetrically reduced bone conduction — not the pattern shown. The air-bone gap of 35 dB is diagnostic of a conductive component. - **Conductive loss that resolves with myringoplasty alone**: While myringoplasty may improve the conductive component, it cannot restore cochlear function once sensorineural damage has occurred. The reduced bone conduction thresholds indicate irreversible cochlear damage that will persist despite TM repair. **High-Yield:** CSOM audiogram evolution: early = pure conductive (air-bone gap, normal bone conduction); chronic = mixed (air-bone gap + reduced bone conduction from cochlear toxin damage). This distinction drives management — early intervention prevents progression to mixed loss. [cite: Dhingra ENT 7e — CSOM pathophysiology and audiological progression]