Correct Answer: B. Left conductive hearing loss
Conductive hearing loss is defined by a significant air-bone gap (typically >15 dB) with normal bone conduction thresholds. The patient's left ear demonstrates exactly this pattern: air conduction is impaired while bone conduction remains normal. The central tympanic membrane perforation is the anatomical basis—it disrupts the mechanical transmission of sound through the ossicular chain, preventing efficient coupling of airborne vibrations to the inner ear. Bone conduction bypasses the middle ear entirely (vibrations travel directly through bone to the cochlea), explaining why it remains unaffected. The "popping" sensation and recurrent ear infections are classic signs of middle ear pathology. In India, tympanic perforation from chronic suppurative otitis media (CSOM) is endemic, especially in children and young adults with poor otologic care access. The PTA pattern—air-bone gap on the affected side with normal bone conduction—is pathognomonic for conductive loss. This is the fundamental discriminator: bone conduction normal + air conduction impaired = conductive loss. Sensorineural loss would show both air and bone conduction thresholds elevated equally (no air-bone gap).
Why the other options are wrong
A. Left sensorineural hearing loss — Sensorineural loss would elevate BOTH air and bone conduction thresholds equally, producing no air-bone gap. The patient's bone conduction is normal, ruling out inner ear or retrocochlear pathology. This is the classic NBE trap—students who forget the definition of air-bone gap may confuse any hearing loss with sensorineural loss. C. Right conductive hearing loss — The right ear shows normal air and bone conduction thresholds bilaterally—no hearing loss at all. The clinical findings (perforation, popping, recurrent infections) are all localized to the LEFT ear. Choosing the wrong ear reflects failure to correlate PTA results with otoscopic findings. D. Right sensorineural hearing loss — The right ear is completely normal on PTA. This option combines two errors: wrong ear selection AND wrong type of hearing loss. It represents a fundamental misreading of the audiometric data and clinical presentation.
High-Yield Facts
- Air-bone gap >15 dB with normal bone conduction = conductive hearing loss (pathognomonic pattern on PTA).
- Tympanic membrane perforation disrupts ossicular chain coupling, impairing air conduction while bone conduction remains intact.
- Chronic suppurative otitis media (CSOM) is the most common cause of tympanic perforation and conductive loss in India.
- Bone conduction pathway bypasses the middle ear entirely—vibrations travel through bone directly to the cochlea, unaffected by ossicular or tympanic pathology.
- Central perforation (vs. marginal) typically causes conductive loss; marginal perforations may lead to ossicular erosion and mixed loss.
Mnemonics
ABC of Hearing Loss on PTA Air-bone gap present → Conductive loss. Air-bone gap absent (both elevated equally) → Sensorineural loss. Use this to instantly classify any PTA result. Bone Conduction = Bypass Bone conduction bypasses the middle ear—if bone is normal but air is down, the problem is in the middle ear (conductive). If bone is also down, the problem is in the inner ear (sensorineural).
NBE Trap
NBE pairs tympanic perforation with hearing loss to lure students into reflexively choosing sensorineural loss. The trap is forgetting that perforation causes conductive loss (mechanical disruption), not sensorineural loss (neural/cochlear damage). The air-bone gap is the discriminator.
Clinical Pearl
In Indian outpatient ENT clinics, CSOM with tympanic perforation is the most common cause of conductive hearing loss in young adults. Recognizing the air-bone gap on PTA is critical for triaging patients to ossiculoplasty or myringoplasty rather than unnecessary imaging or cochlear evaluation.
_Reference: Bailey & Love Ch. 60 (Otology); Robbins Ch. 29 (Ear pathology); Harrison Ch. 29 (Hearing and equilibrium)_