Page 5 of 29

EN4.13 | Otosclerosis — SDL Guide (Part 2)

Diagnosis and Differential Diagnosis

The diagnosis of otosclerosis is a clinical-audiological diagnosis: a young adult (typically female) with bilateral progressive CHL, normal TMs, absent stapedial reflex, type As tympanogram, and the Carhart's notch on PTA — in the absence of a history of ear disease — constitutes a classic presentation that does not require histological confirmation. Definitive diagnosis is intraoperative: the surgeon confirms stapes fixation directly at surgery.

The diagnostic confidence is strengthened by a positive family history, onset in the second or third decade, worsening with pregnancy, and the finding of paracusis Willisii. When the presentation is atypical — early onset, unilateral, or associated with sensorineural loss — HRCT temporal bone adds important information.

Differential diagnosis — causes of CHL with intact TM in a young adult:

The critical clinical skill is to distinguish otosclerosis from other causes of CHL without perforation:

Condition	Key differentiating features
Otosclerosis	Bilateral, young adult, positive FH, As tympanogram, absent reflex, Carhart's notch, no ear disease history
Tympanosclerosis	Calcified plaques visible on TM or in middle ear; usually follows CSOM or trauma
Ossicular chain discontinuity	Large air-bone gap (50–60 dB), Ad tympanogram (hypermobile), history of trauma or CSOM
Malleus/incus fixation	Rarer; similar audiogram to otosclerosis but fixation confirmed at surgery
Superior semicircular canal dehiscence (SSCD)	CHL + bone conduction thresholds apparently better than 0 dB (pseudo-CHL); positive Tullio's phenomenon; CT confirms bony defect
Middle ear effusion (glue ear)	Type B tympanogram (flat, no peak); common in children; seen in adults with Eustachian tube dysfunction

The most practically important differential is tympanosclerosis versus otosclerosis: both cause CHL with an intact TM. The distinction is usually clear — tympanosclerosis leaves visible white calcified plaques on the TM or in the middle ear, and there is typically a history of recurrent ASOM or CSOM. If in doubt, HRCT is helpful, but the final distinction is made at surgery.

Management of Otosclerosis

Management of otosclerosis follows three pathways — medical therapy, surgical correction, and hearing amplification — chosen based on disease activity, degree of hearing loss, patient preference, and surgical fitness. Surgery remains the gold standard for patients with significant air-bone gap and serviceable cochlear function.

1. Medical management — sodium fluoride

Sodium fluoride (20–40 mg/day orally, typically combined with calcium carbonate and vitamin D) is used to arrest the progression of active otosclerosis. Fluoride ions are incorporated into the hydroxyapatite crystal of the newly forming otosclerotic bone, making it more resistant to further resorption and stabilising the disease process. Critically, sodium fluoride does NOT restore hearing that has already been lost — it only arrests further deterioration. Indications include active disease (rising bone conduction thresholds indicating progression, positive CT activity/halo sign), pregnancy (avoiding surgery during pregnancy while suppressing disease progression), elderly or medically unfit patients who are not surgical candidates, and patients who decline surgery. Treatment is typically given for 2–3 years. Side effects include gastrointestinal upset; very high doses (not used therapeutically) can cause skeletal fluorosis.

2. Surgical management

Surgery aims to restore mechanical sound transmission by replacing the fixed stapes with a mobile prosthesis. Two closely related operations are performed:

Stapedectomy: The original Shea procedure (1958). The entire stapes (arch and footplate) is removed, and a prosthesis is placed from the incus long process to the oval window (which is covered with a tissue graft — typically a vein or fat graft). This provides excellent hearing restoration but carries a risk of perilymph gusher (rupture of the inner ear membrane) with total SNHL.

Stapedotomy: The modern standard of care. Instead of removing the entire footplate, a small fenestra (0.6–0.8 mm) is drilled or lasered in the footplate using a microdrill or CO2/KTP laser. A piston prosthesis (most commonly a Teflon-wire or titanium piston) is inserted through this fenestra from the long process of the incus into the vestibule. Stapedotomy has largely replaced stapedectomy because:
- Smaller oval window opening reduces risk of perilymph fistula and sensorineural loss
- Better long-term hearing results
- Easier revision if needed

Outcomes of surgery:
- Closure of air-bone gap to within 10 dB: achieved in >90% of cases in expert hands
- Disappearance of Carhart's notch on post-operative audiogram (confirms the notch was mechanical)
- Sensorineural hearing loss ('dead ear') risk: approximately 1–2% per operation
- Taste disturbance (chorda tympani injury): 10–20%, usually temporary
- Vertigo: transient in most; persistent in <5%
- Perilymph fistula, infection, prosthesis displacement: rare complications

3. Hearing aids

A well-fitted hearing aid is an effective non-surgical option for patients who are poor surgical candidates, those with bilateral disease who wish to defer surgery, or those who decline surgery. Bone-anchored hearing aids (BAHA) are an option when conventional aids are poorly tolerated. Hearing aids are also the preferred option when the cochlear reserve is poor and the air-bone gap is primarily from cochlear otosclerosis.

Self-Assessment: Otosclerosis

Use the following retrieval questions to consolidate your understanding before moving on. For each question, formulate your answer without looking back — then verify. When self-assessing clinical content, it is more useful to attempt a brief verbal explanation than simply to pick an option. Otosclerosis has a high examination yield because it combines physiology (bone remodelling, ossicular mechanics, tuning-fork interpretation), histopathology (spongiotic bone), audiological pattern recognition (As tympanogram, Carhart's notch), and surgical technique — making it a rich OSCE and written-examination topic. Before checking answers, try to reconstruct from memory the full diagnostic picture — the typical patient, the audiological findings, the mechanism of Carhart's notch, and the choice between observation, sodium fluoride, stapedotomy, and hearing aid. This integrative recall is the most reliable preparation for clinical viva questions.

Key concept checks:
- Why is the otic capsule uniquely susceptible to otosclerosis compared to other skull bones?
- What is the Schwartze sign and what does its presence imply clinically?
- In which direction does Weber lateralise in unilateral otosclerosis, and why?
- Why does sodium fluoride arrest disease but not restore hearing?
- Name two ways stapedotomy differs from stapedectomy.
- What happens to the Carhart's notch after successful stapedotomy, and what does this confirm?
- What tympanogram type would you expect in otosclerosis, and how does it differ from glue ear?