OTOSCLEROSIS: From Causes to Complications

Definition

Otosclerosis is a common disorder of the bony labyrinth with a normal tympanic membrane.

It is characterized by gradually progressive CHL as a result of stapes fixation. Though there is no cure, the treatment of choice is surgery which is stapedectomy.

Anatomy

The labyrinth consists of three parts: membranous labyrinth, perilymphatic labyrinth and bony labyrinth.

The bony labyrinth has three layers: endosteal, bony (enchondral), and periosteal

1. Membranous labyrinth (Otic labyrinth or endolymphatic labyrinth): Otic labyrinth consists of the utricle, saccule, cochlear duct (scala media), semicircular ducts, and endolymphatic duct, and sac.
   It is filled with endolymph.
2. Perilymphatic labyrinth or space (Periotic labyrinth): Periotic labyrinth surrounds the otic labyrinth and is filled with perilymph. It consists of a vestibule, scala tympani, scala vestibuli and perilymphatic spaces of semicircular and endolym[1]phatic ducts.
3. Bony labyrinth (Otic capsule): It consists of three layers: endosteal, enchondral and periosteal.

Etiology

The exact cause of the disease is yet not known. The following factors have been documented in the literature:

• Heredity: About 50% of the cases give positive family history. The remaining cases are sporadic. An autosomal dominant inheritance with penetrance in range of 20–40 has been reported.

• Osteogenesis imperfecta: About 50% of cases of type I osteogenesis imperfecta develop hearing loss, histological changes, and COL1A1 expression that are indistinguishable from otosclerosis.
  Patients of osteogenesis imperfecta have a history of multiple fractures. The van der Hoeve syndrome presents with the triad of osteogenesis imperfecta, otosclerosis, and blue sclera.

• Viral: Many reports suggest that otosclerosis may be related to a persistent measles virus infection of the otic capsule.

Types of OTOSCLEROSIS

1. Stapedial otosclerosis:

Stapedial otosclerosis is the most common variety. It causes stapes fixation and presents with conductive deafness.

2. Cochlear otosclerosis:

It involves a region of the round window and areas in the bony labyrinth, and the petrous part of the temporal bone.
It presents with irreversible SNHL, which is probably caused by toxic materials liberated into the inner ear fluid.

3. Histologic otosclerosis:

Histologic otosclerosis is diagnosed only on histological examination. The patient remains asymptomatic.

Clinical Features

• Hearing loss: Gradually progressive Conductive Hearing Loss with the normal tympanic membrane. In most cases, the disease is bilateral.
• Race: White races are affected more than blacks. It is common in Indians but rare among Chinese and Japanese.
• Age of onset: Patients are usually between 20–30 years of age. The disease is rare before 10 and after 40 years.
• Hormonal effect: In females, deafness seems to worsen or manifest during pregnancy and menopause.
• Trauma: Some patients try to correlate deafness with an accident or a major operation.
• Paracusis willisii: In this phenomenon the patient’s hearing improves in noisy background. It happens because a normal person raises his voice in noisy surroundings and patient takes advantage of that. The speech discrimination is not affected in pure conductive hearing loss.
• Tuning fork tests and audiometry show CHL.
• Tinnitus: It is usually present in cochlear otosclerosis and active lesions.
• Vertigo: It is an uncommon symptom. the cause of it is not well understood. Hypertension and metabolic disorders are usually present in these cases.
• Speech: Low, monotonous, well-modulated soft speech.  
• Otoscopy: Tympanic membrane is normal and mobile. Schwartz sign: It is a reddish hue seen through the tympanic membrane on the promontory. It indicates active focus, which is vascular.
• Eustachian tube: Its functions are normal.

Audiometry

1) Conductive hearing loss is more for lower frequencies.

2) Carhart’s notch: There is a dip (from 500–4,000 Hz) in bone conduction curve, which is maximum (15 dB) at 2,000 Hz (5 dB at 500 Hz, 10 dB at 1,000Hz, 15 dB at 2,000 Hz and 5 dB at 4,000 Hz). The Carhart’s notch disappears after successful stapedectomy surgery.

3) Air-bone gap: The degree of footplate fixation is estimated by the size of air-bone gap.

4) Audiometry does not predict the pattern and extent of oval window involvement. It is determined on exploratory tympanotomy during the stapedectomy surgery.

5) Mixed hearing loss with SNHL element indicates cochlear otosclerosis.

Differential Diagnosis

They include the following causes of CHL. They can be differentiated with the help of ear micro examination, siegalization, impedance audiometry, and exploratory tympanotomy:

 1. Serous otitis media

2. Adhesive otitis media

3. Tympanosclerosis

4. Attic fixation of head of malleus

5. Ossicular discontinuity

6. Congenital stapes fixation

Treatment

There is no curative treatment.

Earlier, the treatment of choice is STAPEDECTOMY, where the stapes footplate was completely removed.

Now, the TREATMENT OF CHOICE IS STAPEDOTOMY AND STAPES PISTON PLACEMENT.

A stapedotomy is a small hole drilled and/or lasered in the footplate to facilitate the placement of a prosthesis/piston through the footplate. Surgery is considered successful if the air-bone gap is closed to 10 dB or less.

Other modalities of management include —–

a) Sodium fluoride therapy, and

b) Hearing aids.

c) Stapes mobilization and fenestration operations are performed occasionally.

Sodium fluoride: Sodium fluoride hastens the maturity of active focus and arrests further SNHL.

Stapedectomy: Stapedectomy operation consists of removal of the fixed stapes and insertion of prosthesis between the incus and oval window. Various types of prosthesis include Teflon piston, stainless steel piston, Tefwire or fat and stainless steel wire. In 90% cases, hearing improves.

Stapes mobilization: About 1% of otosclerotic ears have fibrous fixation of stapes. Stapes mobilization provides good permanent hearing in these cases. Simple mobilization of stapes is not indicated in most of the cases as it commonly results in refixation.

Fenestration operation: In fenestration operation, which is almost abandoned, an alternative window is created in the lateral semicircular canal. The main disadvantage is a postoperative mastoid cavity and an inherent hearing loss of 25 dB.

Hearing aid: Hearing aids offer good hearing results and are indicated in patients who refuse surgery or are unfit for surgery.

Contraindication for surgery

• The only hearing ear: There are about 1% chances of developing dead ear.
• Vertigo: History of vertigo in recent months is usually associated with Meniere’s disease. There is heightened risk of postoperative SNHL.
• Young children: Recurrent Eustachian tube dysfunction commonly causes AOM in children and can displace the prosthesis. The otosclerotic focus is usually active and progresses rapidly in children and can close the oval window.
• Certain occupations:
• Postoperative vertigo can interfere the working in some professions such as athletes and high construction workers.
•  In divers and frequent fliers, air pressure changes can damage the hearing and induce severe vertigo.
• Industrial workers who work in noisy surroundings are more vulnerable to occupational SNHL.
• Local diseases: Otitis externa, tympanic membrane perforation and exostosis should be treated before the stapedectomy.
• Pregnancy: Stapedectomy is avoided.

Complications of STAPES SURGERY

• Sensorineural hearing loss: 2% patients develop SNHL. Slowly progressive high frequency loss has been seen in long term follow-up. 0.5% patients get a “dead” ear.
• Vertigo.
• Loss or distortion of taste sensation.
• Unhealed perforation of tympanic membrane.
• Facial paresis/palsy.
• Perilymphatic fistula.

Postoperative Care and Follow-Up

• Analgesics and antibiotics if needed.
• Avoid straining and blowing of nose.
• Outpatient surgery and discharged after several hours.
• First follow-up the day after surgery
• The patients can begin their office work 1 week after the surgery.
• Second follow-up 2 weeks to a month.
• Annual follow-up for audiometry. SNHL requires sodium fluoride therapy.
• Imbalance, ear fullness, tinnitus and hearing loss indicate perilymph fistula (requiring tympanotomy) or endolymphatic hydrops (responding to medical treatment).##

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