Diagnostic and Management Dilemma of Sudden Hearing Loss

Abstract

Sudden SNHL continues to present a diagnostic and management dilemma to otolaryngologists. This otologic entity should be considered a syndrome with various causes, including acoustic neuromas. Diagnosis is hindered mainly by the limited availability of in vivo evaluation techniques for inner-ear disorders. Despite these challenges, recent animal studies and clinical research have increased our knowledge regarding the effect of corticosteroids on sudden hearing loss. Rarey and Curtis first reported the presence of glucocorticoid receptors in the spiral ligament and in other parts of the human inner ear. Hearing improvement following administration of glucocorticoids might be due to (1) their anti-inflammatory effect; (2) increasing stria vascularis synthesis of Na -K adenosine triphosphatase, which decreases vascular permeability (particularly to circulating immune mediators); and (3) increasing cochlear expression of aquaporin 1 and 3. The pharmakokenetics of the glucocorticoids have been studied by Parnes et al, who demonstrated a much higher penetration of corticosteroids into the cochlear fluids following IT application than with systemic administration. The frequent spontaneous recovery of hearing and the hearing improvement following treatment with corticosteroids are both suggestive of a reversible inner-ear process rather than hair-cell degeneration. Such a reversible process can result from ion-homeostatic disturbances caused by stria vascularis dysfunction that can lead to loss of the endocochlear potential and hearing loss. This might represent a common final pathway of many causes of sudden hearing loss, including viral or bacterial infections, metabolic abnormalities, and vascular and autoimmune disorders. Marzo has done a comprehensive and very informative literature review on the topic of IT steroid treatment for sudden SNHL. He was able to identify 7 such studies, of which 1 was randomized and controlled. The results of these studies are encouraging, and his conclusion that this modality of treatment should be considered when oral steroid treatment fails is reasonable. Since severe and profound sudden SNHL has a very poor prognosis, it is tempting to consider treatment with synchronous administration of systemic steroids and IT perfusion in an effort to improve outcomes. At our institution this option is presented to such patients. For IT perfusions, we use 0.3 to 0.4 mL of dexamethasone (24 mg/ mL) administered with a 30-gauge needle attached to a tuberculin syringe. Three treatments are given at weekly intervals. At present, 24mg/mL dexamethasone is available only in a compounded form prepared by pharmacists. Some of the failures of IT perfusion might be caused by inhibition of steroid absorption by a pseudomembrane covering the round window niche. In a study of 202 temporal bones from 117 patients, 11% of the ears were found to have fibrous tissue or a fat plug, and 21% had an extraneous (false) round-window membrane. Office endoscopy and removal of any obstructive lesions may be warranted in such cases. Our preliminary results with IT steroid perfusion for severe and profound sudden SNHL are not very encouraging at this point. We will be reporting our experience in the near future. As new diagnostic techniques are developed, our ability to treat sudden SNHL will improve. Until then, systemic and IT steroids should be considered the treatment of choice. Prospective and controlled studies should be conducted to determine which corticosteroid is most effective, its optimal dose, and the optimal number of treatments. They also should determine if the use of sustained-release delivery vehicles of corticosteroids to the inner ear is more effective than the repeated intratympanic injections. Finally a standardized method of reporting hearing results would be very helpful.