Chapter 6 Cochlear otosclerosis is a controversial term. Some authors prefer the lengthy term sensorineural hearing loss associated with otosclerosis because the cause-and-effect relationship is unclear. There has also been a lack of definite evidence and an associated lack of comprehensive studies of cochlear otosclerosis. For clarity, we refer to cochlear otosclerosis in this book. Cochlear otosclerosis is a gradually progressive sensorineural hearing loss caused by the direct or indirect enzymatic action of the otosclerotic microfoci in the otic capsule. The sensorineural hearing loss is usually bilateral and symmetrical, and, as in stapedial otosclerosis, it may undergo periods of activation and remission. Pure tone and speech audiometry usually shows either a pure sensorineural hearing loss or a mixed type hearing loss. Pure cochlear otosclerosis without stapedial involvement is a difficult condition to identify. The incidence of cochlear otosclerosis is greater than is generally believed. In a double-blind study on histologic and polytomo-graphic correlations in cochlear otosclerosis, Linthicum et al (1981) found that two thirds of cases had cochlear otosclerosis. The clinical incidence of cochlear otosclerosis, however, is much more difficult to determine. Freeman (1979) compared clinical and polytomographic data in 100 consecutive cases of progressive sensorineural hearing loss and found that 29% of cochlear otosclerosis cases that were suspected on clinical grounds were confirmed by polytomography. Causse and Causse (1991), in an evaluation of 11,062 cases, found a similar percentage of cases (22.9%) suffered from cochlear otosclerosis. They believed that this percentage would have been higher if polytomography had been used systematically. They stated further that the incidence of cochlear otosclerosis in progressive sensorineural hearing loss occurs frequently enough to warrant that such patients be thoroughly evaluated to eliminate the possibility of cochlear otosclerosis. Females are more affected than males, and the age of onset is similar to that of stapedial oto-sclerosis. The clinical development of cochlear otosclerosis depends on the progression of otosclerotic focus. This in turn depends on other factors such as the genetic predisposition of the patient and endocrine factors such as puberty and pregnancy. Because the progress of cochlear otosclerosis depends on wide-ranging factors, the disease process itself undergoes periods of activation and periods of remission. In cases of cochlear otosclerosis, there is usually a dominant family history; the patient usually has relatives who have suffered from proven otosclerosis. The hearing loss may have started or increased during pregnancy or following the use of oral contraceptives. Examination of the tympanic membrane frequently demonstrates a positive Schwartze’s sign. Apart from a sensorineural hearing loss, which is the sine qua non of cochlear otosclerosis, the patient usually experiences tinnitus and vertigo. The most common pattern of pure tone audiogram is the “cookie bite” (see Chapter 4, Fig. 4–1). In cochlear otosclerosis, the audiological pattern is one of end organ disease. The Békésey audiogram is usually a type 2. There is a moderate tone decay of up to 20 dB. Speech discrimination scores of 80 to 90% are typical of cochlear otosclerosis. The short increment sensitivity index (SISI) scores are high (60 to 100%), and loudness discomfort may be present at 10 to 110 dB. The stapedial reflex is usually present (Morrison 1984). Although tinnitus is present in stapedial otosclerosis, the incidence at which it occurs in cochlear otosclerosis is higher. It is encountered in the older age group, especially when combined otosclerosis is present. In pure cochlear otosclerosis, tinnitus is usually the presenting symptom. Endolymphatic hydrops is commonly seen as a complication of cochlear otosclerosis. Benign paroxysmal positional vertigo is also commonly seen. Transient episodes of positional vertigo were commonly seen in about 20% of patients suffering from cochlear otosclerosis, and symptoms of hydrops were seen in about 6% of patients (Morrison 1984). In some cases, there can be little doubt about making a diagnosis of cochlear otosclerosis, whereas in others the diagnosis may not be so apparent. In order to help make an accurate diagnosis with the intent to treat promptly with the appropriate modality, many authors have proposed several criteria with which a diagnosis of cochlear otosclerosis can be made. These criteria are as follows. Shambaugh and Holdermann (1926) stated that for a patient to be labeled as suffering from otosclerosis, three criteria should be satisfied: 1. Insidious onset of hearing loss in early adulthood 2. The absence of any other cause that could be proven to have caused hearing loss 3. Conductive deafness in other members of the immediate family In 1966, Shambaugh delineated six criteria for making a diagnosis of cochlear otosclerosis: 1. A positive Schwartze’s sign 2. A family history of confirmed and surgically proven otosclerosis 3. The presence of symmetrical sensorineural hearing loss in both ears accompanied by stapes fixation 4. A flat, rising, or “cookie bite” audiogram with unusually good speech discrimination for a sensorineural hearing loss
Cochlear Otosclerosis
DEFINITION
INCIDENCE
SIGNS AND SYMPTOMS
SPECIALIZED HEARING TESTS
TINNITUS
VERTIGO
DIAGNOSING COCHLEAR OTOSCLEROSIS
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