Idiopathic sudden sensorineural hearing loss (ISSHL) is defined as an abrupt hearing loss of unexplained aetiology.
Diagnosis is based on the clinical presentation, a sensorineural defect detected with tuning fork tests and on hearing tests.
ISSHL should be treated as a medical emergency and an urgent consultation of an otolaryngologist is indicated.
Spontaneous recovery is common in mild cases.
There is research evidence, albeit limited, to support the early and short term use of glucocorticoids in patients with no contraindications to glucocorticoid treatment.
Incidence and aetiology
ISSHL (or sudden deafness) is an unexplained sensorineural hearing loss of ≥ 30 dB in at least 3 contiguous frequencies occurring over a period of up to 3 days.
The incidence of ISSHL is 8-15/100 000 persons/year.
Proposed aetiologies include inner ear vascular compromise, viral infection, autoimmune disorders, intracochlear membrane rupture and abnormal activation of cellular stress pathways within the cochlea.
Atrophy of the hair and supporting cells of the organ of Corti is often a central histopathological finding. It has been postulated that an abnormal activation of cellular stress pathways could lead to the degeneration of hair cells. The efficacy of glucocorticoid treatment could therefore be explained by the inhibition of the stress pathways.
Clinical presentation
The vast majority of cases of ISSHL are unilateral. The hearing loss may be partial, only involving certain frequencies, or total leading to complete deafness in the affected ear.
The natural course of ISSHL varies, and some patients achieve full recovery whereas others are left with permanent hearing loss of varying severity. Spontaneous recovery is common and occurs in up to 65% of patients.
Signs and symptoms
Sudden loss of hearing. Associated symptoms may include aural fullness and pressure or tinnitus as well as vertigo if the inner ear disturbance is more extensive. The patient should be asked about any particular external circumstances surrounding the hearing loss, such as straining, exertion, pressure fluctuations (flying, diving), medication, a tick bite, upper respiratory tract infection or injury.
In ISSHL, the external examination of the ear is normal.
Tuning fork tests are used to confirm the nature of hearing loss; the Weber test (picture 1) shows sound lateralisation to the unaffected ear and the Rinne test (picture 2) is positive.
The hearing of speech and a whispered voice are impaired on the affected side. During a hearing test, the hearing must be masked in the ear not being tested by using a masking noise (e.g. continuous pressure of the external auditory canal orifice).
A neurological examination should focus on signs of either cranial nerve, brain stem or cerebellar involvement suggestive of a retrocochlear abnormality.
Pure tone audiometry shows air and bone conduction hearing thresholds that are significantly decreased as compared with the contralateral ear or previous audiometry results.
Differential diagnosis
Inflammation of the external auditory canal or impacted cerumen may occlude the ear canal.
Otitis media may cause conductive hearing loss, even though in some cases concomitant cochlear hearing loss is also present resulting in mixed hearing loss.
Herpes zoster oticus (also termed Ramsay Hunt syndrome) is a herpes zoster infection around the ear causing facial nerve palsy, vertigo and hearing loss.
Perilymphatic fistulas are rare and usually preceded by sudden straining, trauma or pressure fluctuations resulting in a fistula formation, usually in a window between the inner and middle ear.
Ototoxic drugs, such as aminoglycosides, cisplatin, furosemide and aspirin may cause hearing loss in case of an overdose.
Vertebrobasilar circulatory disorder, an autoimmune disease, psychogenic deafness and diseases of the central nervous system, such as encephalitis or multiple sclerosis, are rare causes.
Ménière's disease or vestibular schwannoma (= acoustic neuroma, i.e. a benign tumour of the 8th cranial nerve) may sometimes present as sudden hearing loss.
ISSHL should be treated as a medical emergency, and in order to minimise permanent inner ear damage treatment should be initiated as soon as possible. There is little if no benefit of treatment if it is started 4 weeks or longer after the onset of hearing loss.
Since systemic glucocorticoids reduce inflammation and oedema, a short 1-2 week course is generally prescribed (methylprednisolone or prednisolone, initially about 60 mg/day). They also provide effective stress pathway inhibition. There is no definitive evidence on the efficacy of glucocorticoids, and treatment must be given careful, individual consideration taking the adverse effect profile into account Oral Steroids in Idiopathic Sudden Sensorineural Hearing Loss.
If systemic glucocorticoid therapy is contraindicated or ineffective, intratympanic glucocorticoid therapy may be considered.
Excessive exertion should be avoided for 1-2 weeks, and sickness leave may be indicated.
After individual consideration, short-term flying and diving restrictions may be considered.
Noise protection is particularly important both for the affected and the unaffected ear.
Hearing must be monitored until the patient's condition is stable, and the possible need for aural rehabilitation and further investigations should be evaluated.
An MRI scan of the head can be carried out to exclude retrocochlear abnormalities as the cause of sensorineural defects detected in an audiogram.
References
Rauch SD. Clinical practice. Idiopathic sudden sensorineural hearing loss. N Engl J Med 2008 Aug 21;359(8):833-40. [PubMed]
Merchant SN, Adams JC, Nadol JB Jr. Pathology and pathophysiology of idiopathic sudden sensorineural hearing loss. Otol Neurotol 2005 Mar;26(2):151-60. [PubMed]
Wilson WR, Byl FM, Laird N. The efficacy of steroids in the treatment of idiopathic sudden hearing loss. A double-blind clinical study. Arch Otolaryngol 1980 Dec;106(12):772-6. [PubMed]
Rauch SD, Halpin CF, Antonelli PJ et al. Oral vs intratympanic corticosteroid therapy for idiopathic sudden sensorineural hearing loss: a randomized trial. JAMA 2011;305(20):2071-9. [PubMed]
Lawrence R, Thevasagayam R. Controversies in the management of sudden sensorineural hearing loss: an evidence-based review. Clin Otolaryngol 2015;40(3):176-82. [PubMed]