OTOSCLEROSIS

Otosclerosis- syn. Otospongiosis, Hardening of inner ear tissue

Oto - Ear
Sclerosis- Hardening of tissue

Therefore, literally meaning hardening of ear tissue.

Otosclerosis or Otospongiosis is primary disease of bony labyrinth or the inner ear. The irregularly laid spongy bone replace the normal enchondral layer of bony otic capsule. Otosclerosis can cause Conductive deafness mostly, or sensorineural deafness or none depending on the region of disease.

Causes of Otosclerosis

Otosclerosis can be attributed to various facts:

Anatomical basis- Bony labyrinth is indeed hard, made of enchondral bone, which changes rarely. But sometimes, some cartilaginous areas in this bony labyrinth can form new spongy bone, hence hardening the normal structural composition of inner ear.
Hereditary- Otosclerosis has autosomal dominant trait and 50% cases have positive family history.
Race- White races are more prone to otosclerosis and it is common in india but rarely found in chinese and japanese.
Sex- Female:Male is 2:1 but reverse in india.
Age of onset- As disease progresses, hearing loss generally occurs at 2nd-3rd decade of life.
Viral infection- Presence of otosclerotic foci has relation with measles virus just like Paget's disease.

Types of Otosclerosis

Otosclerosis can be classically categorised into 3 types as follows:

1. Stapedial Otosclerosis

Hardening at stapes causes stapedial otosclerosis. Fixation of stapes result in Conductive deafness. The hardening occurs most commonly at "Fistula ante fenestram" which is present just in front of oval window and can occur at other foci too. The different sites of stapedial otosclerosis can be better understood by the following image:

Types of Otosclerosis: (A) Anterior focus (B) Posterior focus (C) Circumferential (D) Biscuit type (E) Obliterative

2. Cochlear Otosclerosis

Hardening occurs around round window. Liberation of toxic materials into inner ear fluid causes Sensorineural hearing loss.

3. Histologic Otosclerosis

Asymptomatic, there is neither conductive nor sensorineural hearing loss.

Pathology of Otosclerosis

Grossly- Chalky white, greyish or yellow when inactive but red (due to increased vascularity) when active.

Microscopically- In immature active lesion, there are plenty osteoblasts and osteoclasts with cement substance, while mature lesion has more layered bone and fibrilllar substance than cementum.

Symptoms of Otosclerosis

Hearing loss- The patient presents with bilateral (both sides) conductive hearing loss without any pain.
Paracusis Willsii- The patient hears better in noisy surrounding as compared to quiet surrounding. This can be attributed to hardened ear ossicles which respond well to stronger vibrations than normal optimal vibrations.
Tinnitus- Ringing sound in ear appears commonly in cochlear otosclerosis active lesion.
Vertigo- Uncommon though
Speech- Patient has monotonous, well-modulated and soft speech.

Diagnosis of Otosclerosis

Otoscopy- Tympanic membrane is normal; Schwartze sign can be demonstrated, i.e, reddish hue on promontory through tympanic membrane.
Tuning fork tests- Negative rinne test (i.e, Bone conduction > Air conduction) for 256,512 and 1026 Hz when stapes fixation is complete.
Weber test- Lateralized to ear with greater conductive loss.
ABC (Absolute Bone Conduction)- Normal, decreased in cochlear otosclerosis.
6. Pure tone audiometry shows loss of air conduction for lower frequencies. Carhart's notch appears best at 2000hz when there is highest hearing loss. Carhart's sign disappears after stapedectomy.

Carhart's notch: Notice sharp notch at 2000Hz

Speech audiometry- Normal
Tympanometry- In later stages, curve of ossicular stiffness is seen.

Treatment of Otosclerosis

1. Medical

There is no medical treatment that cures otosclerosis. Bisphosphonate and sodium flouride have been tried but proved ineffective.

2. Hearing aids-

Less risky and efficient, BIHA (Bone Implanted Hearing Aids) are most convenient.

3. Surgical-

TOR (Total Ossicular Replacement) is performed which involves removal of otosclerotic stapes called Stapedectomy (removal of stapes) /Stapedotomy creation of hole in stapes) followed by placement of a prosthesis between incus and oval window.

(A) Pre-stapedectomy (B) Post-stapedectomy

The Prosthesis so inserted can be either Teflon piston, Stainless steel piston, Platinum-teflon or Titanium teflon piston. The improvement is noteworthy, but may fail for reasons like erosion of incus, displacement of prosthesis or reclosure of window.

Types of prosthesis: (A) Teflon piston (B) Platinum-teflon piston (C) Titanium-teflon piston

Selection of Patient for Stapedectomy

Conductive hearing loss should be around 25-30dB with average air-borne gap of atleast 15dB with Rinne test negative for 256 and 512Hz. The patient should be hearing better with hearing aids and speech discrimination should be more than 60% to exclude any substantial sensory component.

Contraindications of Stapedectomy

Only hearing ear
Associated with Menieres disease- Sensorineural hearing loss can occur
Young children- Repeated eustachian tube dysfunction can displace prosthesis.
Profession of athletes, frequent air travelers, divers and construction workers- Post-operative vertigo can cause hindrance in their jobs.
Noisy surrounding occupation- Can cause snsorineural hearing loss due to trauma.
Pregnancy
Otitis externa, TM perforation and exostosis(syn. osteoma, benign overgrowth of per-existing bone)