Otosclerosis

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List of terms related to Otosclerosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: CSN, M.D.

Synonyms and keywords:

Overview

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 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 Lempert’s single-stage fenestration of stapes as treatment.
• 1956:John Shea modernized stapedectomy.

Classification

Based on Symons/fanning grading system otosclerosis can be classified into

• 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)

Pathophysiology

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.

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:

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

Associated Conditions

Conditions associated with otosclerosis include:

• 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.

Causes

Common causes of otosclerosis include:

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

Differentiating ((Page name)) from other Diseases

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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

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Natural History, Complications, and Prognosis

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Diagnosis

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CT scan

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MRI

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Treatment

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Surgery

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References

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