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Otosclerosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] CSN, M.D. Christina Ninan, M.D.

Synonyms and keywords: Otospongiosis

Overview

Otosclerosis -https://commons.wikimedia.org/wiki/File:Gray919.png#/media/File:Gray919.png

Otosclerosis is a word derived from the Greek word "sklērós" 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 infammatory cytokine and cytotxic 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 Lempert’s single-stage fenestration of stapes as treatment.
• 1956:John Shea modernized stapedectomy.

Classification

Based on Symons/fanning grading system

• 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 3:Diffuse confluent cochlear involvement (with or without fenestral involvement)

Embryology

Table explains the embryological process for the development of bony labyrinth

Gestational week	Developmental process
4th week	Development of otic canal from mesenchyme of otic vesicle by forming an otic capsule around it
8th week	Initiation of the cartilaginous framework
16th week	Endochondrial replacement of the cartilaginous framework.

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.

Pathophysiology

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:

Phase	Mechanism of action
Otospongiosis	Increase in both osteoclast activity and microvascularity
Transitional phase	begins with deposits of spongy bone by osteoblasts in areas of previous bone reabsorption
Otosclerotic phase	characterized by spongy bone deposits developing into dense bone that narrows the microcirculation previously developed in the otospongiosis phase

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 pericochlear region, and 19% at the anterior segment of the internal auditory canal.

Etiology

Though the exact cause of otosclerosis is unknown and multiple research studies are still ongoing, several etiologies are the following:

Embryological Cause

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.

Genetic Cause

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

Gender

Women are more likely to have otosclerosis than men , suggesting the role of sex hormones.

Ethinicity

Otosclerosis is more common in Caucasians and Japanese compared to African populations.

Age

Even though otosclerosis could be seen in patients at their twenties and thirties, it usually causes hearing loss only in or after their forties.

Pregnancy

There is no strong evidence why pregnancy worsens hearing loss in some patients with otosclerosis.However 33% women with otosclerosis are found to deteriote in hering after one pregnancy.

Measles

RNA of measles virus was detected at the footplate of stapes in otosclerotic patients , suggesting its role in casuing it, while incidence has reduced significantly in vaccinated populations.

Trauma and Major surgeries also cause otosclerosis.

Autoimmune

Though research on this is in the initial stages, inflammatory cytokine like TNF-alpha and cytotoxic mediators were found at the otosclerotic bone suggesting its role in the pathology.

Differentiating otosclerosis from other diseases

Conditions mimicking Otosclerosis
Serous otitis media Adhesive otitis media Congenital stapes fixation Meniere disease Tympanosclerosis Attic fixation of head of the malleus Ossicular discontinuity Paget's disease

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

Genetic factor

Otosclerosis is an autosomal dominant disease with incomplete penetrance. When 60% of patients were found with family history, 40-50% of patients have it with variable patterns of inheritance. But hearing loss in otosclerosis is found only with family history of the same.

Hormonal conditions

Puberty, pregnancy, and menopause increase the occurrence of hearing loss in pre-existing otosclerosis.

Measles

Persistent measles virus infection of stapes footplate results in activated osteoclast and inflammatory pathways by TNF-alpha mRNA. The protective function of osteoprotegerin at the otic capsule is inhibited by TNF-alpha and its action on RANK production

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.

Clinical presentaion

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%)
• tinnitis (50%)
• Schwartz sign or flemingo's pink sign(not necessary for diagnosis): redness along the promontory of tymphanic membrane on otoscopic examination

Diagnosis

Tuning fork

• Pros of using a tuning fork for diagnosis:
  • 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.

Audiometry and tympanometry

• Caharts notch: Bone conduction depression in threshold at 2000Hz. After stapedectomy caharts notch diappears.
• Tympanometry normal at early disease. In severe cases, flattening and stiffening of curve representing low complaince of ossicular chain and tympanic membrane. Good test to differentiate between otosclerosis and pathologies with low resonance.

CT Imaging

• 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.
• CT Finding: 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.

Treatment

• Medical Management
  • Sodium flouride: Though controversial, it is used to slow the progression of otosclerosis.
  • Bisphosphonates: By inducing osteoclastic apoptosis, bisphosphates cause antiresorptive action, with promising results.
• Hearing aid:It is used alone or in combination with other treatments.
• Surgical Management: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..