Autoimmune Inner Ear disease
Autoimmune inner ear disease is a syndrome of progressive hearing loss and/or dizziness that is caused by antibodies or immune cells which are attacking the inner ear. In most cases, there is reduction of hearing accompanied by tinnitus. The disease results in progressivesensorineural hearing loss (SNHL) that acts bilaterally and asymmetrically, and sometimes affects an individual's vestibular system. It is known in literature that consensus that AIED is the result of antibodies or other immune cells that cause damage to structures of the inner ear such as the cochlea and vestibular system.
- Progressive hearing loss in both ears
Typically will begin in one ear and gradually affect the other
Hearing loss may begin suddenly
- Tinnitus (ringing or buzzing in ears)
- Decrease in word recognition capability
- Loss of balance (vestibular symptoms)
Degree of balance loss can change throughout the course of the disease
Since AIED symptoms are fairly common to many hearing loss disorders, it may be difficult to diagnose AIED without performing multiple medical tests. Some examples of these tests include:
- Hearing Tests for Progressive Hearing and Balance loss
Audiometry (measure of hearing acuity and sound intensity)
Rotatory Chair Test (determines if inner ear is responsible for balance loss)
Electrocochleography (ECOG) (recording of electrical potential in inner ear due to sound)
- Blood Tests for General Autoimmune Diseases
Erythrocyte sedimentation rate (test for inflammation)
Rheumatoid Factor (indicator of autoimmune disorders)
There are also blood tests specific to inner ear disorders:
Anti-cochlear antibody test (testing for antibodies against cochlear cells)
Lymphocyte Transformation Assay (testing whether an individual has developed a T-cell response against a certain drug)
Though it has also been proposed that the use of anti heat shock protein 70 antibodies may be useful in the detection and diagnosis of AIED, there is not enough evidence to confirm the reliability of this method.
The cause of AIED is generally assumed to be related to either antibodies or immune cells that cause damage to the inner ear. There are several theories as to how these might arise, analogously to other autoimmune disorders. There are several theories that propose a cause of AIED:
- Bystander damage - Physical damage to the inner ear may lead to cytokine release that signals for an immune response. This may be a component of the "attack/remission cycle" of Meniere's Disease.
- Cross-reactions - Accidental damage of the inner ear by antibodies or T-cells that recognize an inner ear antigen that is similar to a bacterial or viral antigen
- Genetic factors - Predisposition to developing an autoimmune disorder based on genes inherited
- Intolerance - The immune system may not be aware of all the antigens present in the inner ear until physical damage releases some of these antigens. As a result, the immune system treats these unfamiliar antigens as foreign and mounts an immune response.
Currently, the cross-reactions theory appears to be the favored mechanism of AIED pathogenesis.
AIED treatment is a rapidly changing field. Several medical therapies have been proposed in the treatment of AIED, with corticosteroid therapy being the most effective. However, corticosteroid therapy (specifically with prednisone and dexamethasone) has demonstrated limited effectiveness in some patients, suggesting the need for novel treatment methods. The goal of most AIED treatments is to administer corticosteroids over a certain period of time, re-evaluate hearing at each appointment, and eventually taper off corticosteroid administration. Ideally, patients can be tapered off with hearing fully recovered, though this is the least likely outcome. Often, tumor necrosis factor-α (TNF-α) inhibitors must be administered alongside corticosteroids to achieve a favorable outcome and eventual end to corticosteroid treatment. Recent papers have indicated that the TNF-α inhibitor, infliximab, has the potential to allow for sustained patient improvement and alleviation of symptoms.
Cytotoxic agents such as Cyclophosphamide and Methotrexate have been used in AIED treatment in the past, however findings have suggested limited symptom alleviation from these drugs.