Diagnosing Otosyphillis

The diagnosis of AIED is made by a combination of the clinical presentation, audiometric testing (including test of vestibular function), laboratory evaluation, and response to immunosuppressive therapy. The clinical presentation is by far the most important of these parameters. Some patients note a preceding viral infection, although this is not always apparent. Patients typically present with fluctuating bilateral sensorineural hearing loss, which is progressive over several weeks, with or without vestibular symptoms. In some cases, hearing loss and tinnitus develop unilaterally without contralateral symptoms, thereby confounding the diagnosis. When followed, these patients may develop contralateral symptoms over time, although some do not.

The differential diagnosis includes Meniere's disease, sudden hearing loss, otosyphilis, and cerebellopontine angle masses. Otosyphilis (Chapter 15) is readily excluded by serum analysis, and cerebellopontine angle masses can be identified on magnetic resonance imaging with contrast administration. Sudden hearing loss (Chapter 28) is unilateral and does not fluctuate when followed over time. Meniere's disease is the most difficult diagnosis to differentiate from AIED, because no imaging modality or blood test can identify the disorder. These patients will often present with fluctuating hearing loss and vestibular attacks much akin to AIED; however, Meniere's disease is usually unilateral, whereas AIED is most often but not always bilateral. Most important, idiopathic Meniere's disease does not respond to immunosuppressive therapy (30).

Audiometric testing in such patients is crucial. A pure tone audiogram, tympanometry, speech discrimination testing, and acoustic reflexes are mandatory. Usually, a clear

TABLE 2 Common Systemic Autoimmune Diseases Associated with AIED

Polyarteritis nodosum

Rheumatoid arthritis

Systemic lupus erythematosus

Behget's disease

Crohn's disease, ulcerative colitis

Temporal arteritis

(inflammatory bowel disease)

Sjogren's syndrome

Relapsing polychondritis

Scleroderma

Wegener's granulomatosis

Dermatomyositis/polymyositis

Abbreviation: AIED, autoimmune inner ear disease.

Abbreviation: AIED, autoimmune inner ear disease.

deterioration of the sensorineural levels in both ears can be documented on serial audiometry. Patients will also demonstrate a commensurate deterioration in speech discrimination along with their sensorineural hearing loss. This is important as speech discrimination will often improve after treatement (30a). Other audiometric tests can be helpful. Otoacoustic emissions are typically lost early in the disease course but remain a nonspecific finding. Electronystagmonography demonstrates findings consistent with a peripheral loss of vestibular function, specifically, a reduced caloric response; however, if both ears have degenerated to near the same level at the time of the evaluation, no asymmetry in caloric responses may be noted. Instead, testing to delineate bilateral vestibular loss, such as the rotational chair test, is needed. Patients with bilateral vestibular loss will often display a reduction in gain at lower rotational frequencies using this evaluation. Again, however, this is a nonspecific finding. There have been some patients with AIED who appear to develop oscillopsia and bilateral reduced caloric responses without a demonstrable hearing loss, but this is unusual. The response to immunosuppressives in this situation is unknown.

Laboratory testing is important. Screening for identification of a systemic autoimmune illness that may be undiagnosed at the time of presentation is warranted. It is also important to exclude syphilis as an etiology. A typical battery of tests might include rheumatoid factor, antinuclear antibodies, fluorescent test for treponemes (FTA-ABS), sedimentation rate (ESR), C-reactive protein (CRP), and cytoplasmic and perinuclear antineutrophil cytoplasmic antibodies (c-ANCA and p-ANCA).

Much effort has been expended toward developing a laboratory analysis for identification of AIED. The lymphocyte transformation test and the lymphocyte inhibition assay were used previously but were abandoned due to poor sensitivity and specificity. A Western blot for antibodies against inner ear antigens (Otoblot), particularly the 68 kDa protein, has been developed and is commercially available through Otoimmune Diagnostics, Inc. The Otoblot (Otoimmune Diagnostics, 60 Pineview Drive, Buffalo NY 14228, USA) is positive in a higher percentage of patients with rapidly progressive sensorineural hearing loss than in control patients (31,32). Specifically, in a study of 72 patients with AIED, the Otoblot was identified in 89% of patients with active disease but was not found in patients with inactive disease. This study also found that patients with a positive Otoblot had a 75% rate of hearing improvement when placed on corticosteroids, whereas patients with a negative Otoblot had only an 18% rate of hearing improvement when placed on corticosteroids (4). Another study, of 82 patients with rapidly progressive sensorineural hearing loss, reported the Otoblot test to have a 42% sensitivity and a 90% specificity for corticosteroid response, resulting in a positive predictive value of 91% (33). Kosaka used Western blot to evaluate the sera from 195 patients with sensorineural hearing loss and/or vertigo for reactivity to bovine inner ear antigen and found that 71.5% of patients with moderate or severe hearing loss had a positive reaction to the 68 kDa protein (34). Otoblot for the 68 kDa protein remains the most specific test for corticosteroid-responsive AIED. Other assays such as P0 myelin-associated antibody are currently being investigated as a potential identifying marker of this disease.

Using the clinical presentation, epidemiology, audiometric profile, laboratory tests, and response to immunosuppression as diagnostic factors, a classification for AIED has been developed by Harris and coworkers and is presented as a diagnostic scheme in Table 3.

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