Otosclerosis

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.

• 1704:Antonio Maria Valsalva identified fixation of stapes as a cause of hearing loss.^[1][2][3].
• 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.

Based on Symons/fanning grading system otosclerosis can be classified into:^[4]

• 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)

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.^[5][6]
• 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.

• Accumulation of bone deposits because of increased bone remodeling which is bone resorption followed by bone deposition in the otic capsule result in otosclerosis.^[7]
• Audiological findings are directly proportionate to the extent of bone remodeling.^[8][9]
• 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.

Conditions associated with otosclerosis include:^[10]

• Pregnancy

There is no strong evidence why pregnancy worsens hearing loss in some patients with otosclerosis.However 33% women with otosclerosis are found to deteriorate in hearing after one pregnancy.^[11]

• Measles

RNA of measles virus was detected at the footplate of stapes in otosclerotic patients , suggesting its role in causing 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.^[12]

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.^[13]

Genetic Cause

• Studies have been conducted and found Type 1 collagen gene(COL1A1), a component essential for bone metabolism plays a role in otosclerosis.^[14]
• 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.^[15][16]
• 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

• 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.

Common risk factors in the development of otosclerosis include^[17].

• 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.^[18]

• 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^[19]

Even though otosclerosis appears to be genetic deafness, early prevention can help in combating the disorder and its prevention.^[20]

1. 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.
2. Systematic Bone-conducted audiometry screening: It is done in young children with a family history of otosclerosis.

Post-op complications of otosclerosis include:^[21]

• Perilymph fistula: Progressive hearing loss, Tinnitus, or vertigo.
• Taste disturbance
• Facial nerve injury
• Sensorineural hearing loss
• Post stapedectomy granulomas
• Vertigo

• Most of the patients find improvement in their hearing ability after the surgery.^[22][23]
• 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.

There are no established criteria for the diagnosis of otosclerosis.

Patients present with the following:^[24][25]

• 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

• Pros of using a tuning fork for diagnosis:^[26][27]
  • 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.

• Carhart’s notch: Bone conduction depression in threshold at 2000 Hz.
• After stapedectomy carhart’s notch disappears.^[28]
• 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.

There are no diagnostic laboratory findings associated with otosclerosis.

There are no ECG findings associated with otosclerosis.

There are no x-ray findings associated with otosclerosis.

There are no echocardiography/ultrasound findings associated with otosclerosis.

• High resolution computed tomography (CT) of the temporal bones is the imaging technique of choice in the diagnosis of otosclerosis.^[29][30]
• 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.

There are no MRI findings associated with otosclerosis.

There are no other imaging findings associated with otosclerosis.

There are no other diagnostic studies associated with otosclerosis.

Surgery is the mainstay of treatment for otosclerosis.^{[31][32][33][34][35]}

• Sodium fluoride: Though controversial, it is used to slow the progression of otosclerosis.^[36]
• Bisphosphonates: By inducing osteoclastic apoptosis, bisphosphonates cause antiresorptive action, with promising results.

• Stapedotomy or Stapedectomy along with placement of a prosthesis, has shown a good prognosis with improved hearing ability.^[37][38][39]
• 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.

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

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

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