Sudden sensorineural hearing loss SSNHL
Aetiology: majority 'idiopathic' - many proposed etiologies and risk factors [4].
Postulated causes - viral cochleitis [5], microvascular events 2° hypercoagulable state [6], and autoimmune disorders [7,8]. Herpes simplex type 1 virus (HSV-1) may be involved, analogous to possible role in Bell's palsy [9].
Those with bilateral disease are more likely to be older, to have cardiovascular disease, and to have a positive antinuclear antibody titer [3].
Epidaemiology: incidence SSNHL uncertain, since recovery may be spontaneous + many affected never seek Rx. Estimates of incidence 11 to 77 per 100,000 people per year [1]. Any age – commonly 43 to 53 years old [2], M = F [3].
Risk fx: (observational studies) poor diet (eg, a diet low in fresh vegetables), low serum folate levels, and metabolic syndrome a/w increased risk of idiopathic SSNHL [10-12]
Diagnostic criteria – Most widely accepted criteria • Hearing loss that ^is sensorineural ^is at least 30 decibels (dB) over at least three consecutive test frequencies ^occurs/evolves within a 72-hour period {Definition assumes premorbid hearing in the affected ear similar or identical to hearing in the unaffected ear. Some studies use differing criteria for identifying SSNHL, including loss of 10 to 20 dB in two or three frequencies [15-17], or hearing loss that occurs within 12 hours, including hearing loss noted upon awakening [3]}
Clinical presentation – immediate / rapid dec auditory acuity (or on wakening); usually sensorineural (not conductive)[15]; majority of idiopathic SSNHL are unilateral (bilateral up to 3%)
Many may only notice blocked ear or aural fullness at first, without recognizing reduced hearing
Because a blocked ear is common occurrence and may be attributed to benign conditions (eg, caerumen impaction, serous otitis media), patients may not seek immediate attention.
>90% ipsilateral tinnitus[3,15]; ~50+% with vertigo[18]; occasionally report otalgia or paresthesias [3].
DDx: includes recent ototoxic drug (eg, aminoglycosides, loop diuretics, platinum-based chemotherapy, salicylates), barotrauma, ear or head trauma, or loud noise; Meniere (fluctuates over time), ischemic cerebrovascular disease (ischaemia of anterior inferior cerebellar artery (AICA)[feeds internal auditory (labyrinthine) artery] [22] - usually associated with other neurologic symptoms (eg, ipsilateral Horner, diplopia, nystagmus, facial weakness, limb clumsiness, ataxia, contralateral loss of pain or temperature sensation]; acute otitis media (AOM), chronic otitis media (COM), or mastoiditis (usually ear pain, ear drainage, fever); Lyme (if travel to or residence in a Lyme-endemic region, recent tick bite); acoustic neuroma, Cogan syndrome (association with acute keratitis); autoimmune disease (inc. Sjögren's); vasculitis (inc. PACNS and relapsing polychondritis); meningitis, pachymeningitis, leptomeningeal carcinomatosis, multiple sclerosis, migrainous infarction; vertebral artery dissection may present as occipital or posterior neck pain and isolated early hearing loss [23].
Evaluate hearing loss – check conductive (outer [pinna, ext ear canal] & middle ear [tymp memb, ossicles (malleus-incus-stapes), middle ear space] ) vs sensorineural (inner ear [cochlea {hearing-including Organ of Corti} & vestibule {balance})
Weber- 256Hz tuning fork (long period of tone decay) - vibrating t/fork over midline forehead – SNHL lateralises to normal (contralateral) ear [localises to diseased side with conductive loss]
Rinne – 512Hz t/fork. Cover other ear. Vibrating t/fork on mastoid. Say when °hear – move 3-4cm from canal – hear it? – say when gone; normal occurs when AC > BC (hearing ringing > 2x as long as with bone sensation) SNHL – Rinne usually normal (AC>BC) bilaterally, but “false negative” Rinne (BC>AC, as seen with conductive hearing loss has been reported with severe SNHL
Audiometry - should occur with all patients with suspected SSNHL - ASAP; at most, within 14 days after symptom onset
Imaging - MRI with contrast: check for retrocochlear pathology - should be done within 3 months of onset; if MRI unavailable / not possible, CT temporal bone plus auditory brainstem response (ABR) can be performed
Retrocochlear pathology is the most frequently identifiable cause of SSNHL diagnosed by imaging - one series [21] 550 patients with SSNHL, 3% had retrocochlear tumor (including schwannoma, neurofibroma, or undifferentiated carcinoma); another study [22], vestibular schwannomas identified in 3 - 10 % x SSNHL
Laboratory tests (serology) usually unhelpful (anyone want to comment on anti-hsp70?); in select patients –appropriate laboratory studies based upon clinical suspicion for a particular etiology e.g. CRP, ESR, EPG, viscosity, FBC, TSH
Therapy - Glucocorticoid treatment for all patients with 'idiopathic' SSNHL, starting CS within two weeks of symptom onset (Grade 2C). Options: systemic glucocorticoids, intratympanic glucocorticoids, or combination treatment; modality depends on factors, inc. comorbidities that preclude high-dose systemic CS (eg, diabetes mellitus, previous adverse reaction to steroids), the degree of hearing loss, patient preference
If able to tolerate high-dose systemic glucocorticoid therapy, offer initial treatment with prednisone 60 mg orally once daily for 10 days; otherwise, intratympanic dexamethasone injections once weekly for three weeks; if more severe hearing loss (>50 dB), offer combination therapy (prednisone 60 mg once daily for 10 days plus intratympanic dexamethasone injections once weekly for three weeks, given concurrently or sequentially, in either order).
Salvage therapy for patients with inadequate response to initial treatment – For patients who have an inadequate response after initial therapy (<10 dB improvement in hearing, or who continue to have ≥20 dB hearing loss), suggest salvage glucocorticoid therapy rather than no additional treatment (Grade 2C); ideally initiated within six to eight weeks of symptom onset; treatment depends upon the initial therapy received - i.e. give the one not already given (!)
No additional glucocorticoid therapy is offered to patients who received initial combination systemic and intratympanic glucocorticoids.
Adjuvant HBOT (hyperbaric O2) may be of benefit when used with glucocorticoid salvage therapy for those with an inadequate response to initial treatment, particularly for those patients with a more profound (>70 dB) hearing loss.
Early trial antiviral therapy may be offered if within 48 hours of symptom onset – eg, valacyclovir 1 gram orally three times daily for 7 to 10 days
Evaluate need for hearing amplification and auditory rehabilitation – Patients with permanent hearing loss should be referred to an audiologist for consideration of an assistive hearing device and auditory (aural) rehabilitation
Prognosis - 'generally favourable', especially if mild hearing loss (though pseudo-paradoxically, best hearing gains occur where hearing loss is greatest); ~ two-thirds of patients recover some degree of hearing, although not necessarily complete [3,15,57-60]. [61].
Good prognostic markers - early Dx and Rx; better response if greater deficit; isolated high- or low-frequency hearing loss (compared with a flat pattern hearing loss across all frequencies) [58]; among those with frequency-restricted hearing loss, isolated low-frequency compared with high-frequency hearing loss [63]; presence of tinnitus [58]; absence of vertigo [58,64]
Poor prognostic markers - not improved within three months In general, patients who have are unlikely to experience significant hearing recovery.
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