Idiopathic sudden sensorineural hearing loss (ISSHL) is a medical emergency that presents with the abrupt onset of an unexpected sudden sensory deficit that is often underappreciated by patients, and at times by clinicians. Approximately 88% of sudden sensorineural hearing loss (SSNHL) has no identifiable etiology and is termed ISSHL. Otolaryngologists have intensely investigated ISSHL since the 1970s. Over the past 30 years, more than 800 articles, or 1 every 2 weeks, have been published in the English medical literature.(89) Idiopathic sudden sensorineural hearing loss is the abrupt onset of hearing loss, typically present upon wakening, usually unilateral, and involving a hearing loss of at least 30 decibels (dB) occurring within 3 days over at least 3 contiguous frequencies. As most patients do not present with premorbid audiograms, the degree of hearing loss is usually defined by the presentation thresholds of the unaffected ear. Other associated symptoms include tinnitus, aural fullness, dizziness, and vertigo.
The reported historical incidence of ISSHL ranges from 5–20 per 100,000 population, with approximately 4,000 new cases per annum in the United States.
The true incidence is thought to be higher, as ISSHL is perceived to be underreported. Interestingly, the number of cases per annum appears to be an underestimation as well, as 4,000 cases annually calculates to 1.3 cases per 100,000 with a population estimate of approximately 300 million people in the United States. Calculating an ISSHL incidence rate of 5–20 per 100,000 translates to 15,000–60,000 new cases per annum in the United States. A recent study has reported the annual incidence of ISSHL in the United States is currently 27 per 100,000, and the pediatric incidence is 11 per 100,000. Additional literature states that the incidence of ISSHL is increasing, especially in the elderly, with a recent reported incidence of 77 per 100,000. Others place the incidence of ISSHL at 160 cases per 100,000 and conclude that ISSHL is no longer rare. In 1984, Byl reviewed the literature and found the mean age of ISSHL presentation to be 46–49 years, with variation of ISSHL incidence with age, and an equal gender distribution. The presentation of ISSHL does not appear to have seasonal variations, uneven distributions of presentation throughout the year, or an association with upper respiratory infections, either prior to or following symptom onset. The spontaneous recovery is currently thought to be 30%–60%.
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Source Reference: Excerpted from Hyperbaric Medicine Practice, 5th Edition with permission from the publisher. Reference Chapter 15 by Tracy Leigh LeGros, Heather Murphy-Lavoie.
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