Timothy C. Hain, MD.
Last update: 1/2003
Sudden hearing loss (SHL) is defined as greater than 30 dB hearing reduction, over at least three contiguous frequencies, occuring over 72 hours or less. It occurs most frequently in the 30 to 60 year age group and affects males and females equally. Although called sudden, it seems unlikely that hearing loss is abrupt but rather it probably evolves over a few hours.
SHL can affect different people very differently. SHL is usually unilateral (that is, it affects only one ear); and is often accompanied by tinnitis. vertigo, or both. The amount of hearing loss may vary from mild to severe, and may involve different parts of the hearing frequency range. SHL may be temporary or permanent. About one third of people with SHL awaken in the morning with a hearing loss.
Although some hold that this disease is generally idiopathic (of unknown cause), viral disease appears to be the basis for about 60% of all cases of SHL. Viruses detected at a study at the Massachusetts Eye/Ear infirmary included influenza type B, CMV (Seguira et al, 2003), mumps, rubeola, and varicella-zoster (Harris, 1998). Others include measles, herpes-1, and infectious mononucleosis. Many of these are in the herpes family.
In essence, SHL is diagnosed by documenting a recent decline in hearing. This generally requires an audiogram. Other studies are performed mainly to look for specific causes. The differential diagnosis includes viral disease, Lyme disease and its relative (Lorenzi et al, 2003), vascular disease (1%), autoimmune phenomena, perilymph fistulae and Meniere's disease, and acoustic neuroma (about 4 to 6% of SHL -- see Daniels et al, 2000 for a longer list of diagnoses). Evaluation usually begins with a careful history looking for potential infectious causes such as otitis media and exposure to known ototoxic medications.
Mattox and Simmons (1977) reported a rate of 65% spontaneous recovery to "functional hearing levels." Byl also reported a recovery rate of about 69% (Byl, 1984). Because hearing tends to recover spontaneously at such a high rate, treatment is not always felt necessary, especially when impairment is minor. Those that recover 50% of hearing in the first 2 weeks following SHL have a better prognosis than those who do not recover at this rate (Ito et al, 2002). Recurrence of SHL is rare but possible (Furohashi et al, 2002)
When a treatment of SHL is used, it often consists of burst of steroids such as prednisone. Eisenman and Arts recently reviewed the topic of steroid treatment (2000). Evidence to date for a good effect is mixed. Some studies suggest a better hearing prognosis for treated vs. untreated patients (Haberkamp and Tanyeri, 1999; Alexiou et al, 2001), and others a worse prognosis (Minoda et al, 2000). In the study of Alexiou et al, a better prognosis was associated with very high doses of intravenous prednisolone. Gianoli has recently reported a good response to transtympanic steroids, in persons who were unable to tolerate oral steroids (Gianoli, 2001).
Fattori et al (2001) suggested that hyperbaric oxygen therapy was the treatment of choice. This involved 10, 90-minute sessions of breathing pure oxygen at 2.2 atmospheric pressure in a multiperson chamber. While encouraging, is is difficult to see why this treatment should work and we would like to see this result confirmed with other studies.
Carbogen and MgS04 treatment have also been advocated for SHL (Gordin et al, 2002). At this writing we do not feel that there is enough evidence for either treatment to advocate for its use..
Antivirals seem reasonable, given the frequency that herpes family viruses have been associated with SHL. In a recent animal study, combination treatment with an antiviral (acylovir) and steroids reduced damage in animals whose ears were inoculated with herpes simplex virus type 1 (HSV-1) (Stokroos, 1999), compared to treatment with either acyclovir or prednisolone alone.Similar results were found in a human study by Zadeh et al (2003). On the other hand, Tucci and others found no benefit of Valacyclovir plus steroids over steroids alone in a multicenter study of 84 subjects (Tucci et al, 2002). Medications like acyclovir or valacyclovir may be unhelpful when the cause is a virus that is not in the herpes family, and one rarely knows at the time of the hearing loss which if any virus is responsible. It is also possible that this sort of treatment is just too late in the course of the disorder, as the average time to treat in the Tucci et al study was 4 days. At this writing (5/2002), we would still favor combining steroids and an antiviral, if treatment can be started prior to 4 days.
Haberkamp and Tanyeri recently reviewed the management of idiopathic SHL (Haberkamp and Tanyeri, 1999). They noted that while numerous treatments have been studied aiming to improve blood flow, such as carbogen inhalation or stellate ganglion block, all remain controversial or simply lack convincing evidence of efficacy. Very few placebo controlled studies have performed of treatment of SHL and for this reason, there is presently a limited ability to determine what is the optimal treatment of SHL.
Wang et al recently reported that etanercept given acutely in experimental labyrinthitis resulted in much better hearing results. While this animal study may not apply to humans, it suggests that acute treatment with etanercept or a related anti-TNF drug (Remicade, Humira), may improve hearing results for sterile inflammation.