A 4-year-old boy with acute suppurative otitis media and a bulging tympanic membrane is brought to the ENT clinic. The parents are concerned about possible hearing loss. Which investigation is most appropriate to assess the type and degree of conductive hearing loss in this child?

## Assessment of Conductive Hearing Loss in Acute Suppurative Otitis Media **Key Point:** Air–bone gap audiometry is the gold-standard investigation to characterize and quantify conductive hearing loss by comparing air conduction (affected by middle ear pathology) with bone conduction (bypasses middle ear). ### Why Air–Bone Gap? In acute suppurative otitis media: - **Air conduction (AC) threshold** is elevated (worse) because sound transmission through the middle ear is impaired by fluid/effusion - **Bone conduction (BC) threshold** remains normal because sound bypasses the middle ear and reaches the cochlea directly via skull vibration - The **air–bone gap (AC – BC)** quantifies the conductive component and confirms middle ear pathology ### Audiometric Patterns in ASOM | Hearing Type | AC Threshold | BC Threshold | Air–Bone Gap | Interpretation | |---|---|---|---|---| | **Normal ear** | ≤20 dB HL | ≤20 dB HL | ≤10 dB | No hearing loss | | **Conductive loss (ASOM)** | >20 dB HL | ≤20 dB HL | >20 dB | Middle ear pathology | | **Sensorineural loss** | >20 dB HL | >20 dB HL | ≤10 dB | Inner ear pathology | | **Mixed loss** | >20 dB HL | >20 dB HL | >20 dB | Both middle and inner ear | **High-Yield:** An air–bone gap of **>20 dB** is diagnostic of conductive hearing loss and confirms middle ear involvement in ASOM. ### Mnemonic: **ABC of Audiometry** - **A** = Air conduction (affected in conductive loss) - **B** = Bone conduction (normal in conductive loss) - **C** = Comparison (air–bone gap tells the story) ### Clinical Pearl In children with ASOM, conductive hearing loss is **reversible** once the middle ear effusion resolves. Documenting the air–bone gap at presentation provides a baseline to assess recovery of hearing post-treatment and helps identify persistent conductive loss that may require further investigation (e.g., ossicular fixation, cholesteatoma). ### Why Not the Other Options? **Bone conduction alone (Option 0):** Does not assess the air conduction component and cannot identify the air–bone gap, which is essential for diagnosing and quantifying conductive loss. **Speech discrimination testing (Option 2):** Assesses the clarity of speech perception but does not differentiate conductive from sensorineural loss or quantify the degree of hearing impairment. **Acoustic reflex testing (Option 3):** Assesses stapedial reflex function and can suggest middle ear pathology (absent or elevated thresholds) but does NOT quantify the degree of hearing loss or confirm conductive vs. sensorineural loss.