Otosclerosis
Synonyms and keywords:

# Overview
Otosclerosis is a word derived from the Greek word "skleros" meaning hardening and oto meaning ear. Otosclerosis is an osseous dyscrasia of the otic capsule, which should be an endochondral dense bony part in the labyrinth, replaced by irregularly laid spongy bone leading to the fixation of stapes. It is one of the most common causes of conductive deafness with normal tympanic membranes. Thereby affecting sound transmission to the inner ear at the level of the oval window  Though majority of cases are observed at the oval window, otosclerosis can also affect the round window, cochlear apex, posterior to the oval window, posterior and anterior wall of the internal auditory canal (IAC), cochlear aqueduct, semicircular canals, and within the stapes footplate. It can be asymptomatic or in advanced cases extend into the bony labyrinth and affect cochlea which causes mixed conductive and sensorineural hearing loss depending on the position of foci. Otosclerosis is common in Caucasians and predominantly women. Hormonal fluctuations in women like during pregnancy and menopause may aggravate the disease. Many genetic factors contribute to the development of otosclerosis. And it is an autosomal dominant inheritance with incomplete penetrance. Measles was found to be one of the reasons for otosclerosis. Other factors include inflammatory cytokine and cytotoxic mediators secondary to inflammation. (CT) scanning of the temporal bone can often demonstrate foci of demineralization in the otic capsule in cases of cochlear otosclerosis. The treatment for hearing loss is essentially stapes surgery with successful improvement of 90%-95% in the first 5 years; decreases to 63% after 30years and rarely need revision surgery. Additionally, hearing aid and cochlear implants could be used along with surgery.

# Historical Perspective
- 1704:Antonio Maria Valsalva identified fixation of  stapes as a cause of hearing loss..
- 1841:Toyn bee stated, "osseous ankylosis of the stapes to the fenestra ovalis as one of the causes of deafness".
- 1876:Johannes Kessel described stapes surgery as the treatment.
- 1930-1950: Used Julius Lemperts single-stage fenestration of stapes as treatment.
- 1956:John Shea modernized stapedectomy.

# Classification
- Grade 1: Fenestral Otosclerosis
- Grade 2: Cochlear Otosclerosis
Grade 2A:Basal cochlear turn Otosclerosis
Grade 2B:Middle/Apical turn Otosclerosis
Grade 2C:Both Basal and Middle/apical Otosclerosis
- Grade 2A:Basal cochlear turn Otosclerosis
- Grade 2B:Middle/Apical turn Otosclerosis
- Grade 2C:Both Basal and Middle/apical Otosclerosis
- Grade 3:Diffuse confluent cochlear involvement (with or without fenestral involvement)

# Pathophysiology

## Embryology
Table explains the embryological process for the development of bony labyrinth
- In certain cases, completion of the third stage of bone formation doesn't occur leading to cartilages between bony structures.
- During labyrinth bone formation, the anterior to the oval window is usually the last area to develop. This area is the most common site for otosclerosis.

## Pathogenesis
- Accumulation of bone deposits because of increased bone remodeling which is bone resorption followed by bone deposition in the otic capsule result in otosclerosis.
- Audiological findings are directly proportionate to the extent of bone remodeling.
- Bone remodeling happens  in 3 phases:
- The lesions occur mostly in the anterior to the oval window by calcifying of annular ligament or by involving stapes footplate (80%).
- While 30% of cases have the lesion at the round window,21% have it at peri cochlear region, and 19% at the anterior segment of the internal auditory canal.

## Associated Conditions
Conditions associated with otosclerosis include:
- Pregnancy
- Measles
- Trauma and Major surgeries also cause otosclerosis.
- Autoimmune

# Causes
Common causes of otosclerosis include:
- During the maturation of the otic capsule of the labyrinth, certain places skip the complete conversion to endochondral, leading to irregularly laid spongy bone. This most commonly is seen at fissula ante fenestram.
- Studies have been conducted and found Type 1 collagen gene(COL1A1), a component essential for bone metabolism plays a role in otosclerosis.
- TGF-beta 1(BMP 2 and BMP 4 gene and Angiotensin II (AGT M235T and ACE I/D genes) are also found associated with otosclerosis.
- Other genetic causes for otosclerosis include sex hormones, autoimmune reaction, human leucocyte antigen, inflammatory and regulatory cytokines, parathyroid hormone, and expression of parathyroid hormone-related peptides receptors, and oxidative stress

# Differentiating otosclerosis from other diseases

# Epidemiology and Demographics
- Though a variable pattern of inheritance is observed, 60% of patients report a family with a history of otosclerosis. Thus researchers conclude this condition as an autosomal dominant with incomplete penetrance.
- Greater preponderance in women compared to men in a ratio of 2:1.
- Even though the disease begins in the second and third decade of life, it doesn't result in hearing loss until the fourth decade.
- Clinical prevalence of otosclerosis is found to be higher in Caucasians by 0.04%-1% while the histological incidence of otosclerosis increases to 10% in the same..The incidence  of histological otosclerosis is 1% and 5% in African and Asian population respectively.

# Risk Factors
Common risk factors in the development of otosclerosis include.
- Genetic factor
- Hormonal conditions
- Measles

# Screening
Even though otosclerosis appears to be genetic deafness, early prevention can help in combating the disorder and its prevention.
- Systematic Impedance-audiometry screening: The purpose of this screening is to detect a possible diphasic impedance change (on-off effect) by eliciting stapedius reflex. It is done in school going-children and helps in the early detection of stapedial fixation.
- Systematic Bone-conducted audiometry screening: It is done in young children with a family history of otosclerosis.

# Natural History, Complications, and Prognosis

## Complications
Post-op complications of otosclerosis include:
- Perilymph fistula: Progressive hearing loss, Tinnitus, or vertigo.
- Taste disturbance
- Facial nerve injury
- Sensorineural hearing loss
- Post stapedectomy granulomas
- Vertigo

## Prognosis
- Most of the patients find improvement in their hearing ability after the surgery.
- Only a few don't have any change post-surgery and rarely hearing loss worsens.
- There have been cases where the prosthesis was found displaced from its original position, causing conductive hearing loss again in some patients.
- The second surgery was observed to be less successful than the first.

# Diagnosis

## Diagnostic Study of Choice
There are no established criteria for the diagnosis of otosclerosis.

## History and Symptoms
Patients present with the following:
- Most cases are asymptomatic and diagnosed as an incidental finding in temporal autopsies.
- Bilateral(80%) or unilateral involvement earlier in the disease.
- Progressive hearing loss, which might worsen with lower tone and frequencies like male voices and vowels.
- vertigo(10%)
- tinnitus (50%)
- Schwartz sign or flamingos pink sign(not necessary for diagnosis): redness along the promontory of tympanic membrane on otoscopic examination

## Physical Examination

### Tuning fork
- Pros of using a tuning fork for diagnosis:
Negative Rinne test
Weber test lateralizes to the ear with severe conductive loss.
- Negative Rinne test
- Weber test lateralizes to the ear with severe conductive loss.
- Cons of using tuning fork for diagnosis
Rinne test cannot differentiate between sensorineural hearing loss and normal hearing loss.
Weber test's inability to differentiate a bilateral hearing loss.
- Rinne test cannot differentiate between sensorineural hearing loss and normal hearing loss.
- Weber test's inability to differentiate a bilateral hearing loss.

## Audiometry and tympanometry
- Carhart's notch: Bone conduction depression in threshold at 2000 Hz.
- After stapedectomy carhart's notch disappears.
- Tympanometry normal at early disease.
- In severe cases, flattening and stiffening of curve representing low compliance of ossicular chain and tympanic membrane.
- Good test to differentiate between otosclerosis and pathologies with low resonance.

## Laboratory Findings
There are no diagnostic laboratory findings associated with otosclerosis.

## Electrocardiogram
There are no ECG findings associated with otosclerosis.

## X-ray
There are no x-ray findings associated with otosclerosis.

## Echocardiography or Ultrasound
There are no echocardiography/ultrasound  findings associated with otosclerosis.

## CT scan
- High resolution computed tomography (CT) of the temporal bones is the imaging technique of choice in the diagnosis of otosclerosis.
- However, preoperative CT has little to add in establishing otosclerosis diagnosis and may not even be necessary to confirm diagnosis.
- CT is recommended to be reserved for those patients with presumed additional abnormalities, for specific preoperative planning, or for legal necessity.
- Common CT findings diagnostic of otosclerosis include increased bony radiolucency in the otic capsule around the anterior footplate, thickening of the stapes, and widening of the oval window.
- Early sign on CT: halo sign; demineralized area outlining the cochlea.

## MRI
There are no MRI findings associated with otosclerosis.

## Other Imaging Findings
There are no other imaging findings associated with otosclerosis.

## Other Diagnostic Studies
There are no other diagnostic studies associated with otosclerosis.

# Treatment
Surgery is the mainstay of treatment for otosclerosis.

## Medical Therapy
- Sodium fluoride: Though controversial, it is used to slow the progression of otosclerosis.
- Bisphosphonates: By inducing osteoclastic apoptosis, bisphosphonates cause antiresorptive action, with promising results.

## Surgery
- Stapedotomy or Stapedectomy along with placement of a prosthesis, has shown a good prognosis with improved hearing ability.
- Only rare cases have shown no benefit.
- Revision surgery is controversial but proposed for patients with no improvement of hearing loss, facial nerve damage, or persistent vertigo.
- Most common cause of stapedectomy failure is prosthesis displacement with or without incus erosion.
- Revision surgery is also recommended post surgery for patients with footplate fixation, perilymph fistula, otosclerotic regrowth.
- Post surgery, some are still encouraged to use a hearing aid.

## Primary Prevention
Otosclerosis cannot be prevented but early detection of the disease can help in combating the disease better.

## Secondary Prevention
There are no established measures for the secondary prevention of otosclerosis.