Making the diagnosis

Differential diagnosis

The mistake that matters is mistaking the air–bone gap for otosclerosis and operating on the stapes. One bedside test — the acoustic reflex — usually prevents it.

The otosclerosis trap

Trainee

Both give a low-frequency air–bone gap. But otosclerosis abolishes the acoustic reflexes and gives normal VEMPs, whereas SSCD preserves the reflexes, shows supranormal bone conduction and enhanced VEMPs.1 A stapedectomy for a misattributed SSCD gap does not help and may worsen it.

SSCD against its mimics

SSCD is the reference row; tap a mimic to surface the discriminator. The acoustic-reflex column is the fastest tell.

ConditionKey featureAcoustic reflexes
SSCDreferenceLow-freq air–bone gap + third-window signsPresent
Low-freq air–bone gap (true conductive)Absent
Fluctuating low-frequency SNHLPresent
Pressure-induced vertigoPresent
Autophony of voice & breathingPresent

Tap a mimic to reveal the discriminator. Note the reflex column: absent reflexes flag otosclerosis.

The third-window family & the other vertigos

Posterior- and lateral-canal dehiscence, large vestibular aqueduct and cochlear dehiscence share the third-window mechanism. Among the episodic vertigos, distinguish Ménière’s disease (fluctuating low-frequency SNHL, no sound/pressure provocation), BPPV (brief positional spells) and vestibular migraine. A patulous Eustachian tube causes autophony of the voice and breathing — but not of bodily sounds, and with normal hearing.

Key points

  • Otosclerosis is the key mimic: same air–bone gap, but ABSENT reflexes, normal VEMP, no third-window symptoms.
  • Never proceed to stapedectomy for an SSCD air–bone gap.
  • Related third-window lesions (posterior/lateral canal, large vestibular aqueduct) share the mechanism.
  • Patulous Eustachian tube gives voice/breathing autophony — not bodily sounds — with normal hearing.