Spiral modiolar vein: its importance in viral load of the inner ear

Emerging options in immune-mediated hearing loss

Objective

AIED (autoimmune inner ear disease) is an autoimmune process that leads to the dysfunction of the inner ear, resulting in fluctuating, audiovestibular symptoms. Although the pathogenesis is likely heterogeneous, immune processes within the inner ear ultimately lead to histopathologic changes and sensorineural hearing loss. This review will discuss the latest evidence on treatment options.

Methods

A literature search on articles pertaining to the treatment of autoimmune inner ear disease was performed on PubMed.

Results

Corticosteroid treatment continues to remain as first line therapy for AIED but long-term responsiveness is poor. Cytotoxic chemotherapies can be effective alternatives for steroid nonresponsive patients, but significant side effects may limit their use. Intratympanic steroid injections are beneficial and although there is not enough evidence currently to supplant oral steroid trial they may be a useful adjunct if steroid toxicity is an issue. The efficacy of biologic agents has been variable. Compared to placebo, etanercept does not improve the hearing improvement already attained by steroids alone. However, open pilot studies of other biologic agents show hearing improvements, improvements in tinnitus/aural fullness/vertigo, ability to wean steroid dependency, or benefits in steroid-resistant AIED.

Conclusion

There is currently not enough evidence that alternative treatments supersede the use of initial steroid treatment. Biologic agents and intratympanic steroid injections are relatively well tolerated and should be considered as adjunctive therapy. More studies on the efficacy of various biologics and more studies on the treatment of steroid resistant disease especially after initial benefit are still needed. For those who eventually lose their hearing, cochlear implantation remains as a viable option.

Level of Evidence

expert opinion.

Potential Mechanisms Underlying Inflammation-Enhanced Aminoglycoside-Induced Cochleotoxicity

Aminoglycoside antibiotics remain widely used for urgent clinical treatment of life-threatening infections, despite the well-recognized risk of permanent hearing loss, i.e., cochleotoxicity. Recent studies show that aminoglycoside-induced cochleotoxicity is exacerbated by bacteriogenic-induced inflammation. This implies that those with severe bacterial infections (that induce systemic inflammation), and are treated with bactericidal aminoglycosides are at greater risk of drug-induced hearing loss than previously recognized. Incorporating this novel comorbid factor into cochleotoxicity risk prediction models will better predict which individuals are more predisposed to drug-induced hearing loss. Here, we review the cellular and/or signaling mechanisms by which host-mediated inflammatory responses to infection could enhance the trafficking of systemically administered aminoglycosides into the cochlea to enhance the degree of cochleotoxicity over that in healthy preclinical models. Once verified, these mechanisms will be potential targets for novel pharmacotherapeutics that reduce the risk of drug-induced hearing loss (and acute kidney damage) without compromising the life-saving bactericidal efficacy of aminoglycosides.

Controversies and Criticisms on Designs for Experimental Autoimmune Labyrinthitis

Although immune-mediated inner ear disease was reported around 25 years ago, numerous attempts to identify the inner ear antigens have been performed. Experimental animal models have been used to study the immune mechanisms involved in hearing loss and to develop new therapies. Because animal models of autoimmune labyrinthitis have been developed by means of different antigens, we cannot yet show a valid immunopathologic explanation. A critical analysis of the more relevant experimental models employed has been performed in order to validate the methodology. Comparison between these models and animals with spontaneous systemic autoimmune disease has raised more questions concerning the pathophysiology of autoimmune hearing loss. A new pathogenetic theory is suggested, involving the supporting cells of the organ of Corti.

Autoimmune sensorineural hearing loss: a human temporal bone study

PURPOSE

To describe histopathologic findings in temporal bones of a patient whose clinical history suggests a sensorineural hearing loss (SNHL) of autoimmune origin.

MATERIALS AND METHODS

Temporal bones from a patient with a history of ulcerative colitis, leukemia, and SNHL were examined by light microscopy.

RESULTS

Histopathologic findings included: (1) organs of Corti missing or absent in all cochlear turns; (2) cells decreased in spiral ganglia, and lymphocytic infiltration; (3) absence of portions of the spiral prominence; (4) endolymphatic hydrops in basal, middle, and apical cochlear turns and in the saccule and utricle; (5) fibrosis and osteoneogenesis of a scala tympani of the basal turn of the cochlea, the posterior semicircular canal, and the canal of Cotugno; (6) fibrosis of the vestibular aqueduct and endolymphatic sac; and (7) lymphocytes in the endolymphatic sac, perisaccular area, inferior cochlear vein, and Rosenthal's canal.

CONCLUSION

Histopathologic findings in the temporal bones of this patient with ulcerative colitis, sensorineural hearing loss, and vestibular symptoms closely parallel those in a previously reported animal study of autoimmunity and suggest the possibility of a SNHL of autoimmune origin.

Expression of intercellular adhesion molecule-1 during inner ear inflammation

This study was designed to investigate the expression of intercellular adhesion molecule-1 (ICAM-1) on the spiral modiolar vein (SMV) with its collecting venules (CVs) and the venules of the endolymphatic sac during inner ear inflammation. These data will further elucidate the role of adhesion molecules in extravasation of inflammatory cells from blood vessels during an inner ear immune response. Labyrinthitis was induced in rats by inoculation of keyhole limpet hemocyanin into the scala tympani of animals who had been systemically sensitized to it. Expression of ICAM-1 was examined with a mouse monoclonal antibody to rat ICAM-1 by immunohistochemistry. ICAM-1 was found weakly on the epithelium of SMVs and CVs as early as 6 hours postchallenge, reaching a maximum by day 2 and then fading away gradually. The maximum influx of immunocompetent cells into the cochlea was seen between days 3 and 7. Staining for ICAM-1 was observed on the epithelium of the endolymphatic sac and perisaccular region at 12 and 24 hours, respectively, and this was associated with infiltration of cells into these areas 3 days postchallenge. By day 28, the inner ear had developed endolymphatic hydrops, but at this time it showed almost no significant staining with anti-ICAM-1. The molecule was also expressed in the mesothelium of perilymph, the perineurium of cochlear nerves, the spiral ligament, and the basal cells of the stria vascularis following immunization. Our data provide evidence that endothelial cells of the SMV and its CVs, as well as other inner sites, have the potential to express ICAM-1. This expression precedes the influx of immune cells; therefore, it is possible that this ligand plays a pivotal role in the onset of inflammation in the inner ear. This study also confirmed that the immune response results in endolymphatic hydrops as a long-term consequence.