Medical Treatment of Otosclerosis

Any treatment that can arrest the progression of deafness in cochlear or combined otosclerosis must be given serious consideration. Even those who deny the very existence of cochlear otosclerosis admit that mixed deafness can occur in otosclerosis and can have devastating consequences. This cannot be remedied by surgery alone. Thus, alternative therapies need to be considered for these situations, especially in arresting the progress of sensorineural hearing loss associated with otosclerosis.

Shambaugh and Scott (1964) first suggested that sodium fluoride in moderate dosages could promote recalcification and reduce bone resorption in an active otosclerotic focus. In another study, Petrovic and Shambaugh (1966) reported the effects of this treatment on laboratory animals. They found that sodium fluoride accelerates the calcification of bone and the healing of fractures by inducing speedy formation of a callus and slowing down the decalcification that precedes the healing of fractures.

In humans, fluoride is very effective on the active otosclerotic focus, although it is not that effective on an inactive focus. It was found in vitro that otosclerotic lesions take up radioactive calcium much more readily if fluoride is added to the culture medium.

Sodium fluoride is a trace substance found naturally in varying concentrations (between 0.1 and 16 parts per million) in ground water. Some local authorities add fluoride to drinking water to increase the concentration to 1 part per million, and this has proven very effective in preventing cavities in teeth.

Bernstein et al (1966) examined rural communities in North Dakota and found that there was an abnormally low fluoride content in the drinking water, which was accompanied by a high incidence of osteoporosis. Daniel (1969) compared the incidence of stapedial fixation in an area of low fluoride concentration with that in an area of high fluoride concentration in the drinking water. He found that stapedial fixation was four times higher in the low fluoride concentration than in the high fluoride concentration. Petrovic and Shambaugh (1966) demonstrated in animal studies that with an optimum dose of fluoride bone resorption decreases and calcification increases. They also indicated that their dosages were very minimal, well below the minimum lethal dosage, thereby indicating that sodium fluoride is a very safe drug in therapeutic dosages.

Fluorides act by reducing bone resorption and increasing osteoblastic bone formation. Causse et al (1973) postulated that in otosclerosis fluorides have an antienzymatic action on proteolytic enzymes that are cytotoxic to the cochlea. Sodium fluoride is effective only when the otosclerotic focus is active. Sodium fluoride reduces osteoclastic bone resorption and at the same time promotes osteoblastic bone formation. In new bone the fluoride ion replaces the hydroxy radical in hydroxyapatite; the resulting fluorapatite is harder, of better quality, and more resistant to bone resorption than hydroxyapatite.

Sodium fluoride in optimum dosages accelerates the healing of fractures by hastening the calcification of the callus formation. Fluoride prevents cortisone-induced osteoporosis. It also promotes maturation of active otosclerosis by reducing vascularity and bone resorption activity and by increasing new bone formation to eventually produce inactive otosclerosis. Petrovic and Shambaugh (1966) found that acid phenylphosphatase, the enzyme of bone resorption, is markedly elevated in organ cultures of active otosclerosis. After short-term sodium fluoride therapy of 6 months, the enzyme begins to decline. After long-term fluoride therapy, the enzyme was found to decline to low levels. Petrovic and Shambaugh (1966) measured the uptake of radioactive calcium in organ cultures and discovered it to be increased by spongiotic (active otosclerotic focus) bone. Following short-term fluoride therapy, they noted a significant additional increase of calcium uptake as bone deposition is stimulated. After fluoride therapy for more than 1 year, the calcium uptake was found to decline markedly to that found in inactive otosclerosis. It must be noted that in all of Petrovic and Shambaugh’s work, the dose of fluoride was critical; the optimum dosage used in adults was 60 mg daily.

RATIONALE FOR THE USE OF SODIUM FLUORIDE IN OTOSCLEROSIS

The rationale for the use of sodium fluoride for the treatment of cochlear or combined otosclerosis is based on the following evidence in the literature. Daniel (1969) demonstrated that there is an increase of stapedial otosclerosis in areas where the levels of fluoride were low. Petrovic and Shambaugh (1966) demonstrated in young rats that sodium fluoride in optimum doses promoted new bone formation and reduced bone resorption. The rationale also follows reports that changes occur in the clinical and radiological conditions of patients suffering from cochlear or combined otosclerosis when sodium fluoride is administered.

Causse and colleagues (1993) found that sodium fluoride influences underlying bony changes in the labyrinth so as to arrest or prevent the onset of hearing loss. Sodium fluoride is an enzyme inhibitor, reduces osteoclastic bone resorption, and, if the dosage is more than 60 mg a day, may rebuild pseudohaversian bone.

CLINICAL DATA ON THE EFFECTIVENESS OF SODIUM FLUORIDE

Causse and colleagues (1981, 1982) presented their findings from 648 perilymph samples taken during stapedectomies performed from February 1976 through September 1980. They studied microdosages of three selected enzymes: trypsin, alpha₁-antitrypsin, and alpha₂-macroglobulin; in each of the samples, the enzymes’ relationship with cochlear deterioration expressed in decibels of bone conduction decreased in pure tone audiometry testing. The authors discovered that fluoride not only inhibits direct trypsin inhibition but also results in an overall reduction in enzymatic values in the perilymph of otosclerotic patients.

INDICATIONS FOR THE USE OF SODIUM FLUORIDE

Sodium fluoride can be administered under the following circumstances:

1. Patients with surgically confirmed otosclerosis who demonstrate progressive sensorineural deafness disproportionate to age

2. Patients who present with sensorineural deafness (cochlear otosclerosis). These patients should have a family history of otosclerosis. Their age of onset should be early, with an audiometric pattern suggestive of oto-sclerosis. They should also have good speech discrimination. Forquer et al (1986) examined the effectiveness of fluoride in the treatment of cochlear otosclerosis in 94 patients with cochlear otosclerosis and 98 patients with stapedial otosclerosis and sensorineural hearing loss. Fluoride halted or slowed the progression of sensorineural hearing loss in 63% of patients with cochlear otosclerosis and 46% of patients with stapedial otosclerosis. In their study, the single factor that predicted which patients would respond most favorably to treatment was rate of progression before treatment. Fluoride therapy was successful for 79% of the patients losing their hearing at a rate of 5 dB or more per year at one or more of the speech frequencies. The researchers thus concluded that patients with more rapid rates of progression responded most favorably to fluoride therapy. In other words, the most active otosclerotic lesion responded the most to fluoride.

3. Patients with radiological changes compatible with those of otosclerosis

4. Patients with a positive Schwartze’s sign

5. Patients who have otosclerosis and also are diagnosed to present with secondary hydrops

6.