Otosclerosis 

Ankylosis of the stapes was first described by Valsalva in 1704. Toynbee described fixation of the stapes to the margins of the oval window in 1841 and found similar cases in 136 of 1,000 temporal bone dissections.^[1] The histologic features of otosclerosis were demonstrated by Politzer, who identified the problem as an otic capsule disorder characterized by abnormal new bone formation.

Otosclerosis surgery has developed through 3 distinct eras. The mobilization era began in the late 1800s when Kessel attempted stapes mobilization without ossicular chain reconstruction in cases where it was noted to be fixed. Later, Jack removed the stapes, leaving the oval window open.^[2] Both techniques allowed increased transmission of sound through the oval window but did not use middle ear amplification structures. Furthermore, fatal cases of meningitis from intraoperative exposure of perilymph to bacteria occurred, and any gains in hearing frequently were temporary because any remaining stapes footplate often refixed.

The fenestration era began in 1923, when Holmgren created a fistula in the horizontal semicircular canal and sealed it immediately with periosteum.^[3] This procedure allowed sound conduction preferentially through the fistula, rather than the ossicular chain. Sourdille popularized the procedure when his 3-stage technique was widely published during the 1930s.^[4] Lempert developed a 1-stage technique for horizontal semicircular fenestration, which went on to gain worldwide acceptance after it proved to enhance hearing.^[5] Results, however, were short-lived because the fenestra often resealed with bone.

The stapedectomy era began before the fenestration era closed. Rosen revisited stapes mobilization in 1952.^[6] Later, Shea removed the stapes, sealed the oval window with an autograft vein wall, and then reconstructed the sound-conducting mechanism with an artificial prosthesis.^[7]

This technique gained wide acceptance and has been improved since inception. In the 1970s, Myers conducted stapedotomy using a piston prosthesis. In the early 1980s, Perkins began using the laser for stapedotomy in a procedure in which a small hole is made in the footplate, as opposed to complete or subtotal removal. Several techniques and approaches are commonly used today, with largely excellent results. A few challenges remain, such as those patients enduring sensorineural hearing loss and unsteadiness, but many think surgical treatment for otosclerosis has reached perfection.

Evidence has recently mounted that the measles virus plays an important role in gene activation of otosclerosis. This hypothesis is supported by a declining incidence of otosclerosis since measles vaccinations became widespread as well as finding measles virus RNA in the footplate of otosclerosis specimens.

Otosclerosis is an osseous dyscrasia limited to the temporal bone. Slowly, progressive conductive hearing loss results.

Frequency

Otosclerosis affects 10% of the white population. Frequency, as mentioned above, is thought to be decreasing secondary to measles vaccination.

Otosclerosis is inherited in an autosomal dominant pattern with incomplete penetrance. Women are 2 times more likely to develop the disease than men. Otosclerosis is generally limited to the white population.

The exact cause of otosclerosis is unknown. Measles virus RNA is found in otosclerotic foci in footplates removed during surgery. Measles virus infection may activate the gene responsible for otosclerosis. Otosclerosis, however, is not responsible for all cases of stapes ankylosis. A heterogeneous group of disorders, including other bone degenerative disorders, appears to cause stapes fixation and conductive hearing loss.

The lesion is a pleomorphic replacement of normal bone with spongiotic or sclerotic bone. The histiologic disease progresses in stages. Bony resorption and replacement with new spongy bone characterize early lesions. Osteolytic osteocytes appear at the leading edge of the lesion, and sheets of connective tissue can be observed replacing the bone. Formation of dense sclerotic bone in areas of previous resorption signifies the late phase of otosclerosis. The result is disorganized bone, increased population of osteocytes, and enlarged marrow spaces containing vessels and other connective tissue. Spaces are later replaced by dense sclerotic bone with narrow vasculature and few recognizable haversian systems. Pleomorphism is largely due to normal coexistence of both stages of otosclerosis in any single temporal bone.

Initiating lesions often neighbor the fissula ante fenestram and expand via vascular channels. In 80-90% of patients, lesions are limited to the anterior oval window and affect its pathology by calcification of the annular ligament or by involving the stapes. Both processes result in characteristic conductive hearing loss. In 8% of patients, the process involves the cochlea and parts of the labyrinth (labyrinthine otosclerosis), resulting in sensorineural hearing loss. Approximately 2% of patients display both labyrinthine and ossicular chain involvement.

Explanation of the clinical portion of sensorineural loss has been difficult, but investigators theorize that enzymes from the inner ear lesion diffuse via the spiral ligament to suppress neuron and hair cell activity.

As with any disease, a careful history and thorough physical examination are prerequisites. Often this process reveals a family history of otosclerosis. After compiling this information, audiometric evaluation helps to narrow the differential diagnoses. Pregnancy and estrogen therapy have been reported to accelerate the progression of otosclerosis.

Symptom onset usually occurs by the early third decade of life, but onset is not unusual later in life. Symptoms include slowly progressive hearing loss, which is bilateral in 70% of cases. Vertigo is uncommon. Tinnitus may be present and often resolves after successful surgical management.

Otosclerosis is often associated with osteogenesis imperfect (van der Hoeve syndrome) in a classic triad of hearing loss (conductive, mixed, or sensorineural), spontaneous bone fractures, and blue sclera.

On physical examination, patients with conductive hearing loss often exhibit low-volume speech because they perceive their own voices louder because of the enhanced bone conduction of sound. Otoscopic examination findings are usually normal, although 10% of patients demonstrate a Schwartze sign, characterized by a reddish-blue hue over the promontory and oval window niche areas, secondary to rich vascular supply associated with immature bone. Tuning-fork examination reveals signs of conductive hearing loss.

Early in the disease course, pure-tone audiometry usually demonstrates low-frequency conductive hearing loss. High-frequency losses begin to manifest with gradual air-bone gap widening. If cochlear involvement is not present, otosclerosis is limited to maximal conductive loss of 50-65 dB across all frequencies. If cochlear involvement is present, a mixed hearing loss appears, with high frequencies more affected. In severe cases, tinnitus may interfere with pure-tone audiometry.

Stapes fixation produces an audiometric artifact known as the Carhart notch, which is characterized by elevation of bone conduction thresholds of 5 dB at 500 Hz, 10 dB at 1000 Hz, 15 dB at 2000 Hz, and 5 dB at 4000 Hz. A Carhart notch may also be seen in cases of incudostapedial joint detachment and incus or malleus fixation.^[8] Cochlear otosclerosis is characterized by the presence of mixed or primary sensorineural hearing loss where air-bone gaps are minimal, and the speech discrimination scores are better than what would be anticipated with the degree of hearing loss.

Tympanometry usually reveals a type As or A tympanogram. Acoustic reflexes are often abnormal and may provide the earliest evidence of otosclerosis. Observed abnormality depends on the stage of disease. Almost half of the healthy population may show an initial increase in compliance at stimulus onset, but compliance increase observed at offset occurs only in stapedial fixation and is virtually pathognomonic. Advancing fixation affects both ipsilateral and contralateral acoustic reflexes, even in unilateral disease.

In most cases, discrimination is much better than would be expected with the level of hearing loss. Low speech discrimination scores prognosticate poorly for postsurgical hearing improvement.

In cases of well-advanced lesions and in lesions with vestibular symptoms, several presentation variations are possible in addition to the classic presentation. Patients with advanced lesions can present with no measurable hearing, in which case they are best identified by history. This far-advanced otosclerosis often presents with a family history of hearing loss or a gradually progressive hearing loss that starts early in adult life. Previously obtained audiograms help differentiate this process from other, more common, causes of profound sensorineural hearing loss, especially if measurable hearing existed with previous air-bone gaps.

History of bone-conducting hearing aid use and clinical benefit from hearing aids, even with lack of measurable hearing improvement, supports the diagnosis. Tuning-fork responses are also suggestive of this diagnosis. These patients may benefit from a stapes procedure prior to consideration of a cochlear implantation. Successful stapes surgery may improve hearing thresholds to a point at which conventional hearing aids may be beneficial.

McCabe described otosclerotic inner ear syndrome was described in 1966 as episodic vertigo and a usually unilateral conductive hearing loss.^[9] Vestibular symptoms have been found in approximately 10% of patients with otosclerosis. Suggested mechanisms include end-organ or neural degeneration or biochemical derangement in the perilymph by contact of the disease process. A stapes surgery can improve the symptoms, but endolymphatic hydrops should be ruled out prior to consideration of otosclerosis surgery.

For excellent patient education resources, visit eMedicine's Ear, Nose, and Throat Center. Also, see eMedicine's patient education article Tinnitus.

Other causes of conductive hearing loss (eg, trauma, infection) should be considered before procession to stapes surgery. Indications for surgical management of otosclerosis include conductive hearing loss with a greater than 20 dB air-bone gap. Patients should have the ability to tolerate the procedure in supine position.

See Pathophysiology.

Coexistent Ménière disease significantly increases the possibility of residual hearing loss in the operated ear. Documented dilation of the vestibule or the vestibular aqueduct on CT scanning or MRI also negatively effects hearing outcome. A large tympanic membrane perforation should be repaired in a surgery prior to and separate from stapes surgery.

Relative contraindications include prior stapes surgery complications in the contralateral ear, such as a profound sensorineural hearing loss or protracted vertigo, as well as a medically-infirmed patient.

All patients with otosclerosis should be offered the option of wearing a hearing aid prior to proceeding with stapes surgery.