This article is mainly intedend for use by medical professionals.
Sudden hearing loss (SHL) is an emergency clinical condition characterized by a rapid-onset subjective sensation of hearing impairment in one or both ears.
When not recognized and managed promptly, sudden hearing loss may result in persistent hearing loss and tinnitus and reduced patient quality of life.
The National Institute for Deafness and Communication Disorders (NICDC) defines Sudden Sensorineural Hearing Loss (SSNHL) is a subset of SHL that is (a) sensorineural in nature, (b) occurs within a 72-hour window, and (c) consists of a documented decrease in hearing of 30 decibels affecting at least 3 consecutive frequencies, in an ear which was previously normal OR an incremental deterioration in an ear with a pre-existing hearing loss.
Idiopathic Sudden Sensorineural Hearing Loss (ISSNHL) is a diagnosis of exclusion when all conditions causing sudden sensorineural hearing loss are ruled out, based on history, examination, investigation and in some cases by the passage of time.
Sudden Sensorineural Hearing Loss is also known as Acute Cochlear Dysfunction. When the vestibule of the inner ear also is involved, its called Acute Cochleo-Vestibular Dysfunction.
Epidemiology
Studies have shown that sudden hearing loss affects 5 to 27 per 100,000 people annually. About 66,000 new cases are reported per year in the United States.
SSNHL can occur at any age of life, with the peak incidence noticed in the 4th-6th decade of life.
No sex difference is noticed, incidence among males and females are almost identical.
Though the condition is nearly always unilateral, no side predilection exists for SSNHL. It is observed that the condition affects both right and left ears, with similar incidence rates.
It is extremely rare to have bilateral ISSNHL or to develop ISSNHL in another ear in a patient already having unilateral sensory neural hearing loss. The estimated percentage is less than one. Those with bilateral SSNHL are more likely to be older, to have cardiovascular disease, and to have a positive antinuclear antibody titer.
Other risk factors that are associated with increased risk of SSNHL are diet (those low in fresh vegetables), low folate levels, and metabolic syndromes (diabetes, dyslipidemia), chronic otitis media, etc.
Studies have shown that sudden hearing loss is an early predictor of cerebrovascular accidents and with an increased risk for myocardial infarction later in life.
Etiologies
The exact etiology of sudden sensorineural hearing loss remains unclear in most of the cases. In 85-90% cases, exact etiology is unknown and is labeled as idiopathic.
Following are a list of the most common causes of Sudden Sensorineural Hearing Loss.
| Infections | Virus – Most commonly associated with Mumps, Herpes simplex type I (HSV-1), Parainfluenza, Measles, Rubella virus infection which has a direct effect on cochlea causing cochleitis. |
| Other infections are Meningitis, Syphilis, Encephalitis, AIDS, Lyme disease. | |
| Autoimmune | Antigen-Antibody complex-mediated disease (Syphilis, Cogan’s disease, SLE, Antiphospholipid antibody syndrome, Vasculitis) |
| Micro Vascular Events | Occlusion, Thrombosis, Hemorrhage, Vascular spasm |
| Hyper viscosity syndromes (MTHFR Polymorphism), Homocysteine, Sickle cell disease | |
| Membrane rupture | Rupture of inner ear membranes like round window & oval window. Intracochlear membrane rupture as in Menier’s disease. |
| Baro trauma | Tympanic membrane rupture, Intracochlear gas production |
| Hypoxia | Direct cell death |
| Ototoxic drugs | Destruction of cochlear metabolism Aminoglycosides, loop diuretics, antimalarials, cisplatin |
| Demyelination disorders | e.g.: Multiple sclerosis |
| Retro cochlear pathologies | Vestibular schwannoma (Acoustic Neuroma), meningioma |
| Psychogenic | |
| Molecular | Activation of cochlear nuclear factor Kappa B (NFkB) by endogenous or exogenous stimuli |
Among the above causes, the most commonly accepted etiologies are.
- Viral Infections – Viral cochleitis is associated with greater loss of neurons.
- Vascular causes – The cochlea is an organ with a high oxygen demand but with relatively limited vascular supply. Distribution of microcirculation of cochlea due to hyper viscosity produces damage with sludging of red cells and hypoxia.
Clinical presentation
As mentioned earlier, the disease mostly affects people in their sixth decade of life.
Patients with sudden sensorineural hearing loss (SSNHL) typically report an immediate or rapid hearing loss or find that they have lost hearing upon awakening.
Many patients, however, present with a sensation of a blocked or full ear and do not recognize that they have lost hearing.
One-third of patients may have a preceding viral upper respiratory tract infection a few days prior to the mishap.
Mostly the condition is unilateral (affects one side), rarely in less than one percent of cases it may be bilateral.
More than 90 percent of patients experience tinnitus which may or may not resolve with time and impacts the physiological burden of SSNHL.
20-60% of patients have associated vertigo which has a poor prognosis.
Diagnosis
As of today, there exists no gold standard method for the diagnosis of SSNHL. A diagnosis can be reached based on history, clinical examination, and other investigations.
Patients with SSNHL may usually give a history of noise trauma, barotrauma, temporal bone fracture, usage of ototoxic drugs, recent viral infection, etc. Patients should be asked about a history of trauma, ear pain, ear drainage, fever, focal neurologic symptoms, headache, diplopia, recent eye pain or redness, and prior history of hearing loss.
Though it is extremely rare for some systemic diseases to present as SSNHL, chances are there for hypothyroidism, diabetes, blood dyscrasia, hyperlipidemia, autoimmune disease, syphilis, etc. can present as sudden hearing loss.
Physical examination should not reveal signs of otitis media or obstruction in the ear canal and, except for signs related to hearing loss, should be otherwise unremarkable.
All patients should undergo audiometric evaluation for the initial diagnosis and to follow changes over time.
The most important cause of unilateral sudden hearing loss that needs to be ruled out is an acute stroke, typically due to occlusion of the anterior inferior cerebellar artery (AICA), from which the labyrinthine artery arises. AICA occlusion may manifest as ipsilateral Horner syndrome, diplopia, nystagmus, facial weakness, limb clumsiness, ataxia, and contralateral loss of pain or temperature sensation.
Evaluation for vertebral artery dissection should be considered in patients with occipital or posterior neck pain.
A battery of investigations ranging from basic blood count to imaging of the brain and temporal bones are considered and advised by many surgeons. But many of these lab tests are not evidence-based or recommended by guidelines.
- Full blood count & erythrocyte sedimentation rate (ESR)
- Blood Urea, Serum Creatinine,
- Serum electrolytes
- Lipid profile
- Blood Glucose
- Thyroid function tests
- Syphilis serology
- Autoimmune serology
- Contrast MRI to rule out retro cochlear pathologies like acoustic neuroma, brain stem infarctions, multiple sclerosis, etc.
- Computed tomography in cases who cannot undergo MRI scanning.
Laboratory studies should be based on findings from the history and physical examination that suggest a specific etiology that warrants diagnostic studies.
Explorative tympanotomy (surgical opening of the middle ear) is considered when a perilymph fistula is strongly suspected.
Treatment
Sudden Sensorineural Hearing Loss should be considered as an otologic emergency. Prompt diagnosis with proactive treatment should be provided for patients with SSNHL.
No high-quality results exist to recommend or support the use of any single drug as a treatment of choice in SSNHL.
Generally, the treatment is empirical with ideal management involves.
- Bed rest
- Discuss the diagnosis, uncertainty of natural history with the patient.
- Discuss available treatment options and risks associated with each medication.
- Help the patient to select a medication.
In addition to the above, the following treatments are considered.
A short tapering course of oral steroids: Many ENT surgeons consider a short tapering course of oral steroids for all cases of ISSNHL, though there exists no/limited evidence for this. Though the value of steroids in treating ISSNHL remains still unclear, the updated guidelines by AAOHNS suggest that patients with SSNHL be offered treatment with oral glucocorticoids, with the greatest likelihood of some response if started within two weeks of the onset of hearing loss.
Dexamethasone, Prednisolone are the most commonly used oral steroids. Intravenous methylprednisolone 1gm (0.8mg/kg) OR Intravenous Hydrocortisone 100mg twice daily for 3 – 10 days followed by oral prednisolone 60mg (1mg/kg) in tapering dose is practiced by many. The treatment can be extended for up to another 10 days if there is a good response to initial treatment.
Intratympanic steroid injection is the mainstay of treatment for ISSNHL. The recently updated clinical practice guidelines for sudden hearing loss, by the American Academy advice clinicians, to offer or refer to a clinician who can offer, intratympanic steroid therapy when patients have incomplete recovery from SSNHL 2 to 6 weeks after onset of symptoms. Intratympanic steroids are the mainstay of treatment in patients in whom a high dose of systemic steroids cannot be given, like those with diabetes.
Antivirals: Because of the association with Mumps, and HSV-I type of viruses, some otologists consider adding antivirals along with intravenous and oral steroids. But the evidence for this still lacking and no randomized control trials have shown the superiority of antiviral medication plus glucocorticoids compared with glucocorticoids alone.
The most commonly used antiviral drugs are Valacyclovir 1 g three times daily or Famciclovir 500 mg three times daily or Acyclovir 800mg five times daily for 5 days.
Carbogen inhalation: Carbogen is a mixture of 5% Carbon dioxide with 95% Oxygen. Inhalation of carbogen is supposed to increase cochlear blood flow and provides better oxygenation.
Hyperbaric Oxygen Therapy (HBOT): There exists only limited evidence of hearing improvement in patients presenting within 2 weeks of sudden hearing loss. According to the updated AAOHNS Clinical practice guidelines for SSNHL, hyperbaric oxygen therapy is optional.
Rheological agents: Rheological agents’ drugs which modify the viscosity of blood and improves the circulation. Some commonly used such medicines for SSNHL are Hydroxyethyl starch, Pentoxifylline, Naftidofuryl, Dextran, etc. These drugs may increase the cochlear blood flow. But studies have shown no difference between active treatment vs placebo and evidence-based treatment doesn’t support the usage of these drugs.
Other agents: A cocktail of various other drugs are tried in the treatment of sudden hearing loss, but none of them are supported by evidence.
Drugs like Calcium channel blockers, Ginko Biloba, Vitamins (A, B1, B6, B12, C, E), Prostaglandin analog (Taprosten), etc are also used in some studies. But there exists no evidence showing significant differences in treatment outcome with the usage of these drugs.
Dietary/lifestyle modifications: Dietary/lifestyle modifications with Caffeine restriction, Cessation of smoking are also advised and in general found to be helpful.
Guidelines for management of Sudden Hearing Loss
Recently in August 2019, the American Academy of Otolaryngology and Head & Neck Surgery (AAOHNS)’s team, headed by Dr. Sujana S. Chandrasekhar MD, came up with updated guidelines for diagnosis, management, and follow-up of patients with SHL.
The updated clinical practice guidelines provide evidence-based recommendations and treatment for the patients presenting with SHL.
| Summary of 2019 Updated Guideline, Key Action Statements | |||
| 1 | Exclusion of conductive hearing loss | Clinicians should distinguish sensorineural hearing loss (SNHL) from conductive hearing loss (CHL) when a patient first presents with SHL | Strong recommendation. |
| 2 | Modifying factors | Clinicians should assess patients with presumptive SSNHL through history and physical examination for bilateral SHL, recurrent episodes of SHL, and/or focal neurologic findings. | Recommendation |
| 3 | Computed tomography | Clinicians should not order routine computed tomography (CT) of the head in the initial evaluation of a patient with presumptive SSNHL. | Strong recommendation against |
| 4 | Audiometric confirmations of SSNHL | In patients with SHL clinicians should obtain, or refer to a clinician who can obtain, audiometry as soon as possible (within 14 days of symptom onset) to confirm the diagnosis of SSNHL. | Recommendation |
| 5 | Laboratory testing | Clinicians should not obtain routine laboratory tests in patients with SSNHL | Strong recommendation against |
| 6 | Retro cochlear pathology | Clinicians should evaluate patients with SSNHL for retrocochlear pathology by obtaining an MRI or auditory brainstem response (ABR). | Recommendation |
| 7 | Patient education | Clinicians should educate patients with SSNHL about the natural history of the condition, the benefits, and risks of medical interventions, and the limitations of existing evidence regarding the efficacy | Strong recommendation. |
| 8 | Initial corticosteroids | Clinicians may offer corticosteroids as initial therapy to patients with SSNHL within 2 weeks of symptom onset. | Option |
| 9a | Initial therapy with hyperbaric oxygen therapy | Clinicians may offer, or refer to a clinician who can offer, hyperbaric oxygen therapy (HBOT) combined with steroid therapy within 2 weeks of the onset of SSNHL. | Option |
| 9b | Salvage therapy with hyperbaric oxygen therapy | Clinicians may offer, or refer to a clinician who can offer, hyperbaric oxygen therapy (HBOT) combined with steroid therapy as salvage within 1 month of onset of SSNHL. | Option |
| 10 | Intratympanic steroids for salvage therapy | Clinicians should offer, or refer to a clinician who can offer, intratympanic steroid therapy when patients have incomplete recovery from SSNHL 2 to 6 weeks after onset of symptoms | Recommendation |
| 11 | Other pharmacologic therapy | Clinicians should not routinely prescribe antivirals, thrombolytics, vasodilators, or vasoactive substances to patients with SSNHL | Strong recommendation against |
| 12 | Outcomes assessment | Clinicians should obtain follow-up audiometric evaluations for patients with SSNHL at the conclusion of treatment and within 6 months of completion of treatment. | Recommendation |
| 13 | Rehabilitation | Clinicians should counsel patients with SSNHL who have residual hearing loss and/or tinnitus about the possible benefits of audiologic rehabilitation and other supportive measures. | Strong recommendation |
Treatment outcomes
Complete spontaneous recovery is observed in about 50% of cases of SSNHL, even without any treatment.
Complete recovery is defined as recovery of hearing to within 10dB of prehearing loss on pure tone audiometry (PTA) average. Partial recovery is an improvement of pure-tone average within 50% or more of prehearing loss score and no recovery is less than 50% recovery of prehearing PTA average.
Chances of recovery are less if the symptoms persist even after one month.
Presence of vertigo, patients with a flat/sloping audiogram (High-frequency HL), reduced speech discrimination score, and those at extremes of ages (children and adults above 40 years) are found to have a poor prognosis. Association of tinnitus along with hearing loss has no prognostic significance.
Auditory rehabilitation may be required for patients with a permanent hearing loss depending on the degree of hearing loss. The options include conventional hearing aids, bone-anchored hearing aids (BAHA), cochlear implants, etc.
References
- Stachler RJ, Chandrasekhar SS, Archer SM, Rosenfeld RM, Schwartz SR, Barrs DM, Brown SR, Fife TD, Ford P, Ganiats TG, Hollingsworth DB. Clinical practice guideline: sudden hearing loss. Otolaryngology—Head and Neck Surgery. 2012 Mar;146(3_suppl):S1-35.
- Chandrasekhar SS, Tsai Do BS, Schwartz SR, Bontempo LJ, Faucett EA, Finestone SA, Hollingsworth DB, Kelley DM, Kmucha ST, Moonis G, Poling GL. Clinical practice guideline: sudden hearing loss (update). Otolaryngology–Head and Neck Surgery. 2019 Aug;161(1_suppl):S1-45.