Sudden sensorineural hearing loss (SSNHL) should be considered an otologic emergency. This condition, defined as a loss of 30dB in three continuous frequencies over a period of less than three days affects about 1/15,000 people.1 While there are a wide variety of documented causes of SSNHL, which include viral infections, vascular occlusion, cochlear membrane breaks, perilymph fistula, ototoxic medications, autoimmune disorders, Meniere’s disease and neoplasms, in almost all cases no specific cause is found. These cases are presumed to be due to a viral cochleitis. Experimental evidence shows that several viruses cause a clinical picture of SSNHL in experimental animals, including HSV, CMV, and mumps.2
Patients will usually present with a complaint of decreased hearing or noticing sounds are muffled. Associated symptoms of new onset tinnitus, and impaired sense of balance or vertigo. Some patients will not notice or complain of the hearing loss, but will seek medical attention because of these associated symptoms.
The challenge in evaluating these patients is ruling out other causes of hearing loss to determine which patients have a sudden sensorineural hearing loss and need urgent hearing testing and possibly treatment for this problem.
Ear examination with pneumato-otoscopy can rule out wax impaction and tympanic membrane or middle ear problems that can present with a conductive hearing loss. In cases where the exam is difficult or unclear, tuning fork testing can be helpful. A Weber test (512 Hz tuning fork placed on the top of the head) will lateralize toward an ear with a conductive hearing loss, but away from an ear with a sensorineural hearing loss. The Rhinne test, where loudness is compared on the mastoid bone (bone conduction) and beside the ear (air conduction). In a normal ear or with sensorineural loss the Rhinne will be negative (AC>BC), but a conductive loss shows BC>AC.1
Once conductive causes are ruled out, the next important test is an audiogram. Audiologists are aware of this problem, and will make arrangements for an urgent audiogram. Private audiologist can also arrange an audiogram for a minimal charge to the patients. This will document the hearing loss and make the diagnosis of sensorineural hearing loss.
However, if there was some pre-existing hearing loss, it is difficult to determine if documented loss is new without a previous audiogram. However, as bilateral sudden loss is uncommon, any asymmetry should be assumed to be new and treated.
History is likely the greatest source of information about the possible causes of SSNHL. Other investigations looking for causes usually include CBC, ESR, TSH, PTT, INR, and FTA-ABS, and possibly cholesterol and HgA1C. In appropriate cases, ABR can rule out an acoustic neuroma (which occasionally present with sudden hearing loss). MRI can also rule out this lesion as well as MS, but is impractical in all cases of SSNHL. In the vast majority of cases, history, physical exam, and investigations do not lead to a diagnosis and viral cochleitis is presumed to be the cause.
A wide variety of treatments have been proposed for this condition. Only high dose steroid treatment has been shown to be effective in prospective, randomized, double-blind placebo controlled studies. Wilson and colleagues (3) showed that a profound hearing loss (>90dB) was unlikely to recover despite treatment and mild losses tended to recover in most cases (with or without treatment). However, the moderate losses were significantly more likely to recover with a short course of prednisone (78% vs. 38%, p<.025). In this study, they used 60-80 mg of prednisone for 6 days and tapered over a further 6 days. All patients were treated within 10 days of the onset of the hearing loss. This course of therapy is well tolerated by most people, even diabetics. Of course, specific warnings about side effects are warranted.
Antiviral therapy (such as acyclovir) alone or in combination with prednisone has also been increasingly studied due to the evidence of a viral cause of this condition. Animal studies have shown some promise in reducing the damage in a sudden hearing loss induced by HSV inner ear infections.4 However, randomized studies in human populations have not shown any added benefit from this medication when compared to steroids alone.5
Prognosis in idiopathic SSNHL depends significantly upon the degree of hearing loss, with more severe losses much less likely to recover. Age >40 and the presence of vestibular symptoms (vertigo, imbalance, etc) also correlate with a worse recovery. Delayed treatment with steroids also has shown to negatively impact on ultimate treatment.2
A follow-up audiogram is warranted at about 3-6 months after the onset of the hearing loss to document any improvement. At this point, an ABR can also be considered to rule out an acoustic neuroma, depending on the clinical scenario.
Sudden sensory hearing loss should be diagnosed and managed expediently. Most cases are a presumed viral cochleitis, and early identification and referral, leading to early treatment, can improve final outcomes in this condition.
– Gerard Corsten, MD, FRCSC
Thanks to Dr. D Kirkpatrick for reviewing the draft copy of this article. Dr. Kirkpatrick is a Consultant Otolaryngologist at the QE2 Health Sciences Centre in Halifax N.S.
Wilson, WR, Gulya, AJ. Sudden Sensorineural Hearing Loss. In: Cummings, CW et al OtolaryngologyÐHead and Neck Surgery. 2nd Edition, Vol 4. St. Louis, Mosby-Year Book Inc; 1993.
Gulya, AJ. Sudden Sensorineural Hearing Loss. Comprehensive Therapy. 1996; 22(4): 217- 221.
Wilson, WR, Byl FM, Laird N.. Efficacy of Steroids in the Treatment of Idiopathic Sudden Hearing Los: A Double Blind Study. Arch Otolaryngol Head Neck Surg. 1980; 106:772-6.
Stokroos RJ, Albers FWJ, Schirm J. Therapy of idiopathic sudden sensorineural hearing loss: antiviral treatment of experimental herpes simplex infection of the inner ear. Ann Otol Rhinol Laryngol. 1999; 108: 423-8.
Stokroos RJ, Albers FWJ, Tenvergert EM. Antiviral treatment of idiopathic sudden sensorineural hearing loss: A prospective, randomized, double blind clinical trial. Acta Otolaryngol (Stockh). 1998; 118: 488-495.
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