## Understanding CSOM Pathophysiology **Key Point:** In uncomplicated CSOM with intact ossicles, bone conduction should be normal and air-bone gap should be present. However, when ossicular erosion occurs (especially stapes footplate involvement), bone conduction can be affected, creating a mixed or sensorineural component. ### Analysis of Each Statement | Statement | Accuracy | Explanation | |-----------|----------|-------------| | Central perforation in mucosal CSOM | ✓ Correct | Mucosal (safe) CSOM presents with central perforation; squamous (unsafe) CSOM has marginal/attic perforation | | Squamous metaplasia | ✓ Correct | Chronic inflammation causes replacement of normal mucosa with stratified squamous epithelium | | Bone conduction always preserved | ✗ **INCORRECT** | Ossicular erosion (especially stapes) can impair bone conduction, particularly if stapes footplate is eroded | | Ossicular erosion via osteoclasts | ✓ Correct | Chronic inflammation produces cytokines (TNF-α, IL-6) that activate osteoclasts, leading to bone resorption | **High-Yield:** The statement "bone conduction is always preserved" is FALSE because: 1. Ossicular erosion is common in CSOM (incus most frequent, then stapes) 2. Stapes footplate erosion specifically impairs bone conduction 3. This creates a mixed hearing loss pattern, not purely conductive **Clinical Pearl:** A patient with CSOM presenting with bone-conduction threshold worse than normal (>20 dB HL) should raise suspicion for ossicular erosion or cochlear involvement, requiring imaging (HRCT temporal bone) before surgery. **Warning:** Do not assume all conductive hearing loss in CSOM has intact bone conduction—always measure bone conduction thresholds before surgery to detect sensorineural or mixed components.
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