Timothy C. Hain, MD . Return to hearing page Page last modified: March 9, 2013
|Figure 1. Cross section of ear. Otosclerosis involves the small bones of the middle ear, the malleus (2), the incus (3) and the stapes (4), as well as the bone that surrounds the inner ear, which is called the otic capsule.|
Otosclerosis is a disease of the bones of the middle ear. These are labeled the malleus, incus and stapes (2-4) in figure 1, and are also known in aggregate as the "ossicles". The ossicles become knit together into an immovable mass, and do not transmit sound as well as when they are more flexible. An illustration of one form of this called "stapes fixation" is shown in figure 2. Otosclerosis can also affect the other ossicles (malleus and incus) and the otic capsule -- the bone that surrounds the inner ear.
|Figure 2. Stapes fixation in otosclerosis. A bony ankylosis (knee) knits the bone of the middle ear to the stapes, preventing normal transmission of sound from the eardrum into the inner ear.|
Only about 0.3% of the population has otosclerosis (Donaldson and Snyder, 1993). Although hearing loss is usually diagnosed in early adult life, the prevalence increases almost 7-fold with age (Niedermeyer et al, 2001). At autopsy, pathologic otosclerosis is very common (2.5 to 10% of temporal bones).
Hearing loss usually begins between the ages of 11-30. The hearing loss can be of two types. When otosclerosis involves the small bones of the middle ear, a conductive type loss is found. This type of hearing loss can be corrected both by a hearing aid as well as by surgical procedures called stapedectomy and stapedotomy.
When otosclerosis significantly involves the bone which surrounds the inner ear, called the "otic capsule", a sensory type hearing loss occurs. This type of hearing loss is not correctable by stapedectomy. While hearing aids are usually worth trying, they also may be ineffective. When otosclerosis involves both the small bones and the cochlea, a "mixed" type hearing loss occurs.
Tinnitus is common in otosclerosis
NATURAL COURSE OF THE DISEASE
Hearing loss generally begins between the ages of 10 and 30. Early on the disease is called "otospongiosis". During this time there is active remodeling of bone of the otic capsule. There may be no conductive hearing loss at this point but rather there may be a "sensory" type hearing loss. The amount of sensory type hearing loss is correlated with decreased bone minearl density of the cochlea (Guneri et al, 1996). The sensory type hearing loss is attributed to leakage of enzymes from bone into the inner ear (Grayeli et al, 2003). It is this process that is thought to possibly be inhibited by medical treatment (sodium fluoride) -- see following.
Sensory hearing loss is also attributed to atrophy of the spiral ligament caused by involvement of lamellar bone at the inner surface of the cochlear capsule. A third cause is vascular due to degeneration of the stria vascularis. In early stages, treatment with fluoride may be helpful. The sensory component of the disease may eventually lead to complete deafness, but fortunately, this is unusual. Sensorineural hearing loss typically progresses at a rate of 1db/year (Sakihara and Parving, 1999).
Later on, a conductive pattern of hearing loss appears. The conductive type of otosclerosis usually progresses up to a maximum in the 30's. After this, it rarely progresses. Dizziness and imbalance is a feature of otosclerosis in roughly 25% of cases. In about half of all patients, there is a family history of similar problems. Women are affected twice as often as men. People of African-American descent only rarely have otosclerosis -- it is usually a condition found in persons of Caucasian or Oriental descent.
Pregnancy often has an adverse effect. Otosclerosis is often discovered during or just after pregnancy. The effect of hormone supplements post-menopause is unknown. Usually both ears are affected, although in about 10-15% of patients, hearing loss occurs on one side only. This may be mediated by increased activity of the renin-angiotension system (Imauchi et al, 2008). Renin blockers (tekturna -- Aliskiren) are available, as well as many angiotension convertase inhibitors (ACE), but to our knowledge, no one has attempted their use to block worsening of otosclerosis in pregnancy.
Most feel that otosclerosis is an inherited, an autosomal dominant disease with variable penetrance. This means that you have a 50-50% chance of getting the gene for otosclerosis if one parent has it, but that not everyone with the gene develop symptoms. There are some differences in opinion about this - -as about 100% of monozygotic twins match up with respect to otosclerosis (Fowler, 1966). Many genes have been reported, suggesting that the disease is genetically heterogeneous. This would be consistent with the observation that it is of variable penetrance, as one would expect a single gene to be more consistent in behavior.
An association between the COL1A1 gene, related to osteogenesis imperfecta, and otosclerosis has been demonstrated by McKenna (McKenna et al, 1998). The relevance of this observation is presently unclear.
Variants of otosclerosis exist in which there is a mutation in the NOG gene (Brown et al, 2003), as well as numerous other genes on linkage studies. Linkage studies appear to represent types of otosclerosis that do not represent the usual clinical pattern for the disease, and actually may be "red herrings", -- basically an artifact of the way that genetic research is performed and accepted for publication.
Viral plus genetic
As there is also also evidence of viral influences in otosclerosis, a recent hypothesis is that otosclerosis requires a combination of a specific gene with exposure to a specific virus (e.g. measles) for it to be expressed and hearing loss to occur (McGuirt et al, 1998; Karosi, Konya et al. 2004). Nuclear inclusions similar to paramyxoviral nucleocapsids have been observed in otosclerosis osteoclasts (McKenna et al, 1986; Chole and McKenna, 2001).
Blue-grey sclera (i.e. "white" of eye) in individual with both osteogenesis imperfecta and otosclerosis
The gene that predisposes to otosclerosis may be similar to the gene that causes osteogenesis imperfecta -- a generalized bone disease (McKenna et al, 2002), that is generally transmitted in an autosomal dominant fashion. Persons with osteogenesis imperfecta often develop conductive hearing loss, and are treated similarly as are patients with otosclerosis (van der Rijt and Cremers, 2003). Their eyes sometimes have a blue-gray cast, called "blue sclera". This is not a bright blue -- see above. The genes that confer susceptibilty to otosclerosis may also provide some protection against otitis media (Manolidis et al, 2003).
Some feel that chronic measles infection in bone predispose patients to otosclerosis. Viral materials can be found in osteoblasts in otosclerotic lesions (Nadol, 1998) and in the stapes footplates of persons with otosclerosis (Karosi, Konya et al. 2004; Karosi, Konya et al. 2005). On the other hand, about 40% of stapes from otosclerosis patients are negative for measles (Karosi et al, 2007), and it is also unclear why measles should affect the temporal bone, but not affect other bones in the body.
Cases that are virus positive also are positive for TNF-alpha, suggesting a possible link to autoimmune inner ear disease. (Karosi, Konya et al. 2005). To our knowledge, nobody has yet attempted to apply this finding with anti-TNF drugs such as entanercept.
Pathologically, otosclerosis occurs only in human temporal bones, and is considered to be a disorder of new bone formation. The statistics here are rather amazing. Histologic otosclerosis, meaning that it is found only on section but has no symptoms, is found in one of every 2.5 to 10% of whites in the United States (Altman et al, 1967; Declau et al, 2001). Clinical otosclerosis, with involvement of hearing, occurs in one in every 10 patients with histologic otosclerosis (Nadol, 1998). This results in the conclusion that 0.25% to 1% of the population should exhibit clinical otosclerosis. The author's clinical experience suggests that this estimate may be an order of magnitude too high, as practically, otosclerosis is a rare diagnosis and getting rarer. The prevalence of otosclerosis may be dropping due to measles vaccinations (see above).
The most commonly affected portion of the bone around the inner ear (otic capsule) is the anterior oval window (about 96%). It can also involve the round window niche (30%), the internal auditory canal, and occasionally ossicles other than the stapes (Schuknecht and Kirchner 1974; Schucknecht, 1993). Otosclerosis is thought to begin with otospongiosis, which is a localized softening of the normally very hard bone of the otic capsule (Shambough 1971). There appear to be three stages of otosclerosis -resorptive osteoclastic stages with signs of inflammation, followed by an osteoblastic stage involving immature bone, followed by mature bone formation.
Bone in the otic capsule is different from bone elsewhere as it undergoes very little remodeling -- less than 2% per year, compared with 10%/year in long bones (Sorensen, 1994). Bone turnover varies between the bone in the periphery (about 10%/year) compared to the labyrinth (about 0.1%/year) (Frisch et al, 1998). The difference in the rate of turnover is thought to be mediated by osteoprotogerin (OPG). OPH is found in high concentration in the perilymph (Zehnder et al, 2005), and thus lack of OPG might be thought of as a possible explanation for the the otospongiosis part of otosclerosis.
DIAGNOSIS OF OTOSCLEROSIS
Diagnosis is usually made by a combination of family history and a progressive conductive hearing loss. Hearing tests may initially show a sensory pattern and later show the typical conductive loss pattern. Acoustic reflexes may eventually be absent, but early on may show the "on-off" effect.
There is an odd variant of otosclerosis called "cochlear otosclerosis". Some clinical papers (e.g. Lippy and Berenholz) suggest that this condition can be diagnosed with a flat sensorineural hearing loss, good speech discrimination, absent acoustic reflexes, and a family history. To us, this clinical picture would seem rather difficult to distinguish from any other type of sensorineural hearing loss. As the treatments for cochlear otosclerosis vary from doing nothing to an unproven medical treatment (sodium fluoride), we would favor simply diagnosing such patients as having sensorineural hearing loss.
Bedside: The otologic clinician should confirm audiological testing suggesting a conductive hearing loss with bedside examination. The reason for this is that mistakes can be made, and when there is a significant hearing loss, inexperienced audiologists may omit or use masking incorrectly. It is best to confirm the conductive hearing loss both with the tuning fork test (512 hz) -- both Weber and Rinne, and with the VEMP test. VEMP's should be absent in a conductive hearing loss but present in sensorineural hearing loss. Rarely (about 10%) there is a redness of the promentory of the tympanic membrane. This is called Schwartz sign -- it is not a reliable sign and should not be relied upon (Lippy and Berenholz, 2008).
The symptom of paracusis Willisii, where the patient perceives speech better in a noisy background, is said to be frequently present in otosclerosis as well as other causes of conductive hearing loss. It is said to be due to the tendency of people to speak louder in noisy environments. This being said, it is still difficult to see the logic and we ourselves have never seen a patient who has volunteered this observation. Another possible explanation is that persons with sensorineural hearing loss have great problems hearing in noise, perhaps because of loss of outer hair cells, but this is simply not the case in conductive hearing loss.
Dizziness can occur in otosclerosis and was reported in one study to occur in 15% of patients. Pathologically there is degeneration of the vestibular ganglion (Scarpa's ganglion). The mechanism for dizziness is unknown, although there is speculation that it derives from release of enzymes from metabolically active bone into the inner ear (Causse et al, 1982). There are also many papers reporting hydrops in otosclerosis, and thus an overlap with Meniere's is a feasible explanation. Other possibilities might be a "halo" effect -- persons visiting ear doctors may be more likely to attribute dizziness to their ear than others, occlusion of fluid pathways within the inner ear from bony overgrowth, or another effect on the ear caused by the same underlying (? measles ?) cause as otosclerosis.
There are four treatment options:
1. Do nothing is a reasonable option.
Otosclerosis does not have to be treated, as there are no medications that have been shown to work, and it will progress or not independent of any treatment. It is advisable to have a formal hearing test repeated once a year (or earlier if hearing drops). The main reason for this is to exclude alternatives (such as tumors or Menieres-- otosclerosis does not protect you from other ear diseases), and also to keep in touch with the audiologist in regards to when a hearing aid might be indicated.
2. Hearing aids -- A good idea.
Hearing aids are effective for conductive hearing loss and certainly are less risky than having ear surgery. Hearing aid technology has undergone tremendous advances since the invention of surgical treatment for otosclerosis. Bone implanted hearing aids (BAHA), can be especially convenient.
3. Medical treatment -- is generally ineffective
At the present writing, fluoride therapy is no longer a recommended primary treatment for otosclerosis (NIH consensus), because of its effect on other bones including the possibility of increasing the risk of hip fractures. (Riggs et al, 1987; Riggs et al, 1990). It would seem to us, that one would need to consider both the risk of hearing progression, and balance it against the risk of adverse effects on other bones, when prescribing.
Sodium fluoride is a dietary supplement (not a drug). The idea of using fluoride is not unlike that of using it for teeth -- fluoride speeds up hardening of bone. A large uncontrolled study of about 1500 patients by Dr. Shambough and associates (at Northwestern, the author's institution) suggested that it was effective. Nevertheless, this treatment is not widely accepted and has not been proven to be effective. Other more rigorous trials have reported similar results (Bretlau et al, 1989). Some advocate using sodium fluoride for cochlear otosclerosis (Lippy and Berkowitz, 2008). Cruise et al (2010) indicated that there is only low-quality evidence for sodium fluoride therapy being effective in otosclerosis.
The protocol for medical treatment is to use 2-4 tablets/day of Florical plus 400 U of vitamin D. Side effects of fluoride (Florical and Monocal are the two preparations available over the counter) include occasional stomach upset, allergic itching, and increased joint pains. If aggravation of arthritis occurs, the Fluoride is stopped and the joints return to their previous state in a few weeks. In such a situation, patients can "pace themselves", taking as much of the medication as can be tolerated. Monical is a preparation that is absorbed in the intestine rather than in the stomach and may cause less side effects.
Typical doses are one tablet three times a day (florical) and one-two tablets three times a day (Monocal). Aldolescents are treated with 2.2 mg/day of sodium fluoride (Lippy and Berenholtz, 2008). After two years of fluoride treatment, the dose of fluoride is reduced from three times a day to once a day. Once the otospongiosis phase of otosclerosis is over and there is a clear cut otosclerosis documented by conductive hearing loss, fluoride may be stopped. The treatment is continued after surgery.
Brookler has advocated use of medications designed for osteoporosis, the diphosphonate family in otosclerosis (e.g. Brookler, 1997; 2008). A double blinded study found no significant difference (Kennedy et al, 2003). Some studies even report worsening of hearing on these drugs (Yasil et al, 1998), which would be expected if the drug was ineffective. At this writing (2011), it is not clear whether these drugs are helpful.
Lippy and Berenholtz suggest adding Caltrate and 30 mg of risedronate (a biphophonate -- Actonel) in persons who do not respond to Florical and Vitamin D. In other words, a combined approach. To our knowledge, there has been no controlled studies of this suggestion.
Diphosphonates have been associated in rare instances with osteonecrosis of the jaw as well as unusual femoral shaft fractures. As there is no FDA approval for these drugs in otosclerosis, we advise caution.
4. Surgical treatment -- Stapes surgery -- fading out ?
For conductive hearing loss, in 1957, Dr. John Shea invented the procedure of stapedectomy, which produced excellent hearing results, which remain good for many years after the surgery. This procedure may allow avoidance of hearing aids. It, however, does not help the sensory component of the hearing loss and at best, may close the "air-bone" gap. It also does not affect the vertigo that is sometimes associated with otosclerosis. According to Nadol, stapedectomy is indicated in patients with good bilateral inner-ear function, and conductive hearing loss ranging from 25-30 dB in elected frequencies. Stapedectomy is unreasonable if discrimination scores are lower than 65% as this indicates that there is a substantial sensory component. Patients with stapedectomy may attain better results with hearing aids because of the need for lessor amplification.
Stapedectomy may fail for a number of reasons. It is a somewhat difficult and delicate procedure. There may be displacement of the prosthesis, reclosure of the fenestra (window), or erosion of the incus. Disease may progress so that correction of the conductive component is inadequate. At least 10-20% of patients undergo revision survery (Mayer and Lambert, 2004). Hearing loss typically progresses after surgery, with the sensorineural component progressing at the rate of 1 dB/year (Sakihara and Parving, 1999).
Stapes surgery is decreasing (Vrabec and Coker, 2005). This may be due to increasing prevalence of measles immunization, or perhap simply catching up on the backlog of cases that existed before surgery was available.
The author's position on stapedectomy is that there are usually better options -- hearing aids usually work well. To us, the recently developed BAHA implanted hearing aid seems better suited to treatment of otosclerosis than stapes surgery. There are other recent devices that are even less invasive.
Surgery pearls (From Lippy and Berenholz).
Surgery should not be done if the air-bone gap is less than 20 DB. Always test each patient at least twice before doing the surgery (because mistakes can happen). The surgeon should be prepared, if necessary, to repair the ear drum prior to the operation, treat all infections prior to the operation, and remove exostoses at the time of the ear surgery.
Surgery should not be performed on a patient with present acoustic reflexes.
Surgery should also not be performed in patients whose hearing loss is 70 dB or less unless their speech discrimination score is 80% or better.
Otosclerosis surgery is not durable. The disease tends to progress. On revision, "success" rates are approximately 75%. (Lippy and Berenholz, 2008)
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