Otosclerosis

Otosclerosis is a localised disorder of bone remodelling confined to the otic capsule (the dense endochondral bone of the labyrinth) in which normal lamellar bone is replaced by spongy, vascular, immature bone. When this focus fixes the stapes footplate in the oval window, it produces the classic slowly progressive conductive hearing loss of a young adult — a perennial NEET PG favourite because the clues (Carhart notch, paracusis Willisii, As tympanogram, absent reflexes) are crisp and almost pathognomonic.

Definition and key concepts

Otosclerosis (a misnomer — it is really otospongiosis in its active phase) is a primary, focal disease of the otic capsule and ossicles characterised by alternating phases of bone resorption and abnormal new bone deposition. It is histologically present in about 8–10% of temporal bones (histologic otosclerosis) but produces symptoms (clinical otosclerosis) in only about 0.5–1% of the population, because hearing loss occurs only when a focus reaches and fixes the stapes footplate.

High-yield: Otosclerosis affects only the otic capsule — it is a disease unique to the human temporal bone and does not occur in the rest of the skeleton (contrast with otosclerosis-like changes that can mimic but are separate from systemic bone disease).

• Sex: Twice as common in females; classically accelerated by pregnancy (oestrogen effect).
• Age: Symptoms usually begin in the 2nd–3rd decade (20–40 years).
• Race: Most common in whites, rarer in blacks and Asians.
• Laterality: Bilateral in ~70–80%, though often asymmetric.

Etiology and risk factors

The cause is multifactorial. Key associations for the exam:

• Genetic / hereditary: Autosomal dominant inheritance with incomplete (variable) penetrance (~40%) and variable expressivity. A positive family history is common.
• Hormonal: Worsens during pregnancy, lactation and the menopause — supports an oestrogen-sensitive remodelling process.
• Viral (measles): Persistent measles (rubeola) virus RNA has been detected in otosclerotic foci, and otosclerosis incidence has fallen with measles vaccination — a strongly tested association.
• Enzymatic: Increased local autolytic enzymes and proteolytic enzymes drive resorption.

High-yield: Three "favourite" exam associations — autosomal dominant inheritance, pregnancy as an aggravating factor, and the measles virus theory.

Pathology and pathophysiology

The disease passes through two histological phases:

Feature	Active phase (otospongiosis)	Inactive phase (otosclerosis)
Bone character	Spongy, vascular, immature woven bone	Dense, sclerotic, mature lamellar bone
Vascularity	High (numerous vascular spaces)	Low
Cellularity	Many osteoblasts/osteoclasts	Few cells
Otoscopic sign	Flamingo-pink (Schwartze) sign through TM	Absent
Activity on imaging	Lucent foci on HRCT	Sclerotic

Site of onset (the single most asked fact): the focus most commonly begins at the fissula ante fenestram, a small cleft of cartilage just anterior to the oval window. From here it spreads to fix the anterior part of the stapes footplate, gradually progressing to total fixation.

High-yield: Earliest and commonest site = fissula ante fenestram (anterior to oval window). This is why stapedial (fenestral) otosclerosis causes conductive loss.

Types by anatomical spread:

1. Stapedial (fenestral) otosclerosis → stapes fixation → conductive hearing loss (most common, most operable).
2. Cochlear (retrofenestral) otosclerosis → focus reaches the endosteum of the cochlea, releasing toxic enzymes into the inner ear → sensorineural hearing loss.
3. Mixed → both components.

The conductive loss results purely from mechanical fixation of the footplate stiffening the ossicular chain. Because the stiffness most affects low and mid frequencies first, the bone-conduction line itself is artefactually depressed at 2 kHz (the Carhart notch — see audiometry).

Clinical features

The classic patient is a young woman in her 20s–30s with bilateral, slowly progressive painless hearing loss and a normal-looking eardrum.

• Progressive conductive hearing loss — gradual, painless, often bilateral.
• Paracusis Willisii (paracusis of Willis): the patient hears better in noisy surroundings. In noise, people raise their voices; the conductively deaf patient is not bothered by the background noise and so receives a louder signal. Almost pathognomonic of conductive deafness, classically otosclerosis.
• Tinnitus — common, especially in active disease and cochlear involvement.
• Soft, monotonous voice (low-volume speech): because bone conduction is intact, the patient hears their own voice well and tends to speak softly (contrast with sensorineural loss where the patient speaks loudly).
• Vertigo — uncommon; if present consider cochlear otosclerosis or a coexisting balance disorder.
• Schwartze sign: a reddish/flamingo-pink hue seen through the tympanic membrane over the promontory, reflecting the hypervascular active focus.
• Tympanic membrane is normal and the external canal is normal — an important negative that distinguishes it from chronic otitis media.

High-yield: Paracusis Willisii (hears better in noise) + soft speaking voice + normal eardrum + young female = otosclerosis.

Diagnosis and investigations

Diagnosis is essentially clinical + audiological; imaging and surgery confirm it.

Tuning fork tests

Test	Finding in otosclerosis	Interpretation
Rinne	Negative (BC > AC)	Conductive loss; becomes negative once air–bone gap > ~20–25 dB at that frequency
Weber	Lateralises to the worse (more affected) ear	Conductive loss lateralises to poorer ear
Absolute Bone Conduction (ABC)	Normal	Cochlear reserve intact (early disease)
Gelle's test	Negative	Classic for stapes fixation

Gelle's test uses a Siegle's pneumatic speculum to vary middle-ear pressure while a tuning fork is on the mastoid: in a normal mobile ossicular chain, increasing pressure pushes the footplate in and reduces perceived loudness (positive Gelle). In stapes fixation the loudness does not change → negative Gelle, a classic sign of otosclerosis.

High-yield: Gelle's test is negative in otosclerosis (fixed footplate). Carhart notch + As tympanogram + absent reflexes complete the audiologic triad.

Pure tone audiometry (PTA)

• Conductive hearing loss with an air–bone gap, worse in the low frequencies early.
• Carhart's notch: an apparent dip (artefactual depression of the bone-conduction threshold) maximal at 2000 Hz (2 kHz), with smaller dips at 500, 1000 and 4000 Hz. It is not true sensorineural loss — the fixed stapes alters the normal resonance of the ossicular chain, so the masked BC reading at 2 kHz looks worse. The notch typically disappears (BC improves) after successful stapes surgery, confirming it was artefactual.

High-yield: Carhart notch = dip in BC threshold at 2 kHz, characteristic of otosclerosis, reversible after stapedectomy.

Impedance audiometry (tympanometry)

• Type As tympanogram: a shallow tympanogram with normal middle-ear pressure but reduced compliance ("s" = stiff/shallow) — reflects the stiff, fixed ossicular chain.
• Acoustic (stapedial) reflexes: absent (or show an on–off / biphasic "diphasic" pattern in very early disease) because the fixed stapes cannot move in response to reflex contraction.

Tympanogram type	Compliance	Pressure	Classic disease
A	Normal	Normal	Normal ear
As	Reduced (shallow)	Normal	Otosclerosis, malleus fixation
Ad	Increased (deep)	Normal	Ossicular discontinuity, flaccid TM
B	Flat	—	Middle-ear effusion / perforation
C	Normal/reduced	Negative	Eustachian tube dysfunction

Imaging

• HRCT temporal bone is the imaging investigation of choice — shows lucent (otospongiotic) foci around the oval window/fissula ante fenestram and is useful for cochlear otosclerosis ("double-ring" / halo sign around the cochlea) and surgical planning.

Diagnostic flow: Young adult, progressive CHL, normal TM → tuning forks (Rinne −ve, Weber to worse ear, Gelle −ve) → PTA shows air–bone gap + Carhart notch at 2 kHz → tympanometry As with absent stapedial reflexes → HRCT to confirm/plan → diagnosis of stapedial otosclerosis.

Management and treatment of choice

Surgery — the definitive treatment

• Stapedotomy (small-fenestra: a tiny hole is made in the footplate and a piston prosthesis placed) is today's preferred operation — safer, with fewer inner-ear complications and lower risk of dead ear than classical stapedectomy.
• Stapedectomy (the footplate or its posterior part is removed and replaced with a prosthesis, e.g. Teflon piston, with vein/fat/perichondrium graft over the oval window) is the classical procedure.
• Treatment of choice overall = stapes surgery (stapedectomy/stapedotomy).

	Stapedectomy	Stapedotomy
Footplate handling	Removal of (part/all of) footplate	Small calibrated fenestra (~0.6–0.8 mm) + piston
Inner-ear trauma	Higher	Lower (preferred)
Risk of dead/SNHL ear	Higher	Lower
Modern preference	Older standard	Current standard

High-yield: Modern operation of choice is small-fenestra stapedotomy with piston prosthesis; the classic procedure is stapedectomy. Surgery is done on the worse-hearing ear first.

Key surgical points:

• A minimum cochlear reserve / good bone conduction is needed; an air–bone gap of at least ~15–20 dB justifies surgery.
• The best candidate has an air–bone gap with good cochlear reserve and only one ear is operated at a time (never both simultaneously) — the better ear is left untouched in case of a dead ear.
• Single hearing ear is an absolute contraindication to surgery (risk of total deafness if that ear fails).
• Active focus (positive Schwartze sign / pregnancy) is a relative contraindication — surgery may be deferred.

Medical therapy

• Sodium fluoride (with calcium and vitamin D) is used to promote maturation and arrest the active (otospongiotic) focus. Fluoride converts the immature spongy bone to dense mature bone, halting progression of cochlear otosclerosis and reducing tinnitus; it does not reverse established conductive loss. Bisphosphonates are an alternative for active disease.

High-yield: Fluoride arrests (does not cure) active/cochlear otosclerosis by hastening bone maturation; it is given especially for progressive sensorineural loss (cochlear otosclerosis) and a positive Schwartze sign.

Non-surgical / supportive

• Hearing aid is an excellent, safe alternative — especially for patients unfit/unwilling for surgery, with a single hearing ear, or with bilateral disease awaiting surgery. Conductive losses amplify very well.
• Cochlear implant for advanced cochlear otosclerosis with profound SNHL.

Complications

• Cochlear otosclerosis → progressive sensorineural hearing loss and tinnitus.
• Surgical complications: dead ear (total SNHL) — the most feared, perilymph fistula / "gusher", vertigo, facial nerve injury, tinnitus, chorda tympani injury → altered taste, prosthesis displacement/incus necrosis, and recurrence/relapse of conductive loss.
• Floating footplate and perilymph gusher are recognised intra-operative hazards.

Key differentials

Condition	Distinguishing clue
Ossicular fixation/discontinuity	Trauma/COM history; discontinuity gives Ad tympanogram (not As)
Tympanosclerosis	Chalky plaques on TM; preceding chronic otitis media
Serous otitis media (OME)	Type B/C tympanogram, dull/retracted TM, fluid behind it
Adhesive otitis media	Retracted scarred TM, history of recurrent OM
Congenital ossicular fixation	Hearing loss from childhood, non-progressive
Paget's disease / osteogenesis imperfecta (van der Hoeve syndrome)	Systemic bone disease; van der Hoeve = blue sclera + bone fragility + otosclerosis-like CHL
Meniere's / cochlear otosclerosis	SNHL ± vertigo; tympanometry normal

High-yield: Van der Hoeve syndrome = osteogenesis imperfecta triad of blue sclerae + fragile bones + conductive (otosclerosis-like) deafness — a classic eponym MCQ.

Mnemonics and eponyms

• "FAMOUS PAW" to recall the picture: Female, Autosomal dominant, Measles, Otic capsule, Unremarkable (normal) eardrum, Schwartze sign — Paracusis Willisii, As tympanogram, Worse in worse ear (Weber).
• As = "A-shallow / A-stiff" tympanogram → stiff ossicular chain.
• Eponyms to know: Carhart notch (2 kHz BC dip), Schwartze sign (flamingo-pink promontory), Paracusis Willisii (Thomas Willis — hears better in noise), Gelle's test (negative), van der Hoeve syndrome (blue sclera + fragile bones + deafness), fissula ante fenestram (site of onset).

Recently asked / exam angle

• Site of earliest otosclerotic focus → fissula ante fenestram (anterior to oval window).
• Carhart notch is seen at → 2000 Hz (2 kHz) and disappears after successful stapes surgery.
• Tympanogram in otosclerosis → Type As (shallow, reduced compliance, normal pressure); stapedial reflexes are absent.
• Gelle's test negative indicates stapes fixation.
• Paracusis Willisii = hears better in noisy environment → think conductive deafness/otosclerosis.
• Schwartze sign indicates an active (vascular) focus.
• Investigation of choice (imaging) → HRCT temporal bone; double-ring sign in cochlear otosclerosis.
• Treatment of choice → stapedectomy/stapedotomy; modern preference = small-fenestra stapedotomy with piston.
• Sodium fluoride is used to arrest active/cochlear otosclerosis, not to reverse conductive loss.
• Worse ear operated first; never both ears together; single hearing ear is an absolute contraindication.
• Measles virus association and falling incidence after MMR vaccination.
• Pregnancy worsens otosclerosis (oestrogen) → a relative contraindication to surgery during active disease.

Rapid revision

1. Otosclerosis = focal otic-capsule bone remodelling; symptomatic in ~0.5–1%, histologic in ~10%.
2. Autosomal dominant, incomplete penetrance (~40%); commoner in young white females; worsens in pregnancy.
3. Earliest/commonest focus = fissula ante fenestram → anterior stapes footplate fixation.
4. Active phase = otospongiosis (vascular) → Schwartze sign (flamingo-pink promontory).
5. Hallmark = progressive painless bilateral conductive hearing loss with a normal eardrum.
6. Paracusis Willisii (hears better in noise) + soft monotonous voice = classic.
7. Rinne negative, Weber to worse ear, Gelle negative, ABC normal.
8. Carhart notch at 2 kHz on PTA — artefactual BC dip, reversible after surgery.
9. Type As tympanogram + absent stapedial reflexes.
10. Imaging of choice = HRCT temporal bone (lucent foci; double-ring sign in cochlear type).
11. Treatment of choice = stapedotomy (piston) / stapedectomy; worse ear first, never bilateral, single hearing ear contraindicated.
12. Sodium fluoride arrests active/cochlear disease; hearing aid is a safe non-surgical option; van der Hoeve = blue sclera + fragile bones + deafness.