Sudden Sensorineural Hearing Loss

SSNHL (Sudden Sensorineural Hearing Loss) was described by De Kleyn in 1944. Sudden hearing loss is defined as the subjective hearing loss of rapid onset, occurring over 72 hours or less, in usually one or rarely in both the ears (about 1% cases). In the audiometry test, there is 30-35 dB or more of SNHL in at least three consecutive frequencies. Though it is rarely seen. It is an otological emergency. The severity of the hearing loss may vary from mild to total loss which can be permanent. SSNHL may be accompanied by roaring type tinnitus or there are incidences of mild transient vertigo which may also be associated with nausea and vomiting.

 

Natural history. Patients first notice their hearing loss with or without associated tinnitus on awakening in the morning and often presents with a full or blocked ear. It can be unilateral or bilateral. As this is a common and non-specific symptom it can be underestimated by both patients and clinicians, thus leading to a delay in evaluation and treatment.

Prognosis. The prognosis is not as bad as is generally supposed. Approximately 50% of patients spontaneously return to a normal hearing without any treatment. Spontaneous recovery of normal hearing is more likely to occur if good prognosis factors are present.

Good prognosis factors:

1. Early treatment.
2. If the recovery phase starts within 2 weeks. Shorter the delay between the onset of SSNHL and the onset of recovery, the better the prognosis for complete recovery.
3. Young age patients below 40 yrs.
4. No history of vertigo.
5. An Audiogram showing mild hearing loss with the involvement of low and mid frequencies.

Poor prognosis factors:

1. Late treatment.
2. If the recovery phase starts after 2 weeks.
3. Old patients above 60 yrs.
4. History of vertigo.
5. An audiogram showing severe to profound hearing loss with the involvement of high frequencies. A downward sloping audiogram is associated with a poorer prognosis.

Aetiology

Viral infections, vascular obstruction, breaks or rupture in the cochlear membranes have all been described as possible etiologic factors for idiopathic sudden deafness. Perilymph fistulae may occur in the oval or round window as a result of physical trauma such as a blow to the head or ear, barotrauma, acoustic trauma, surgical trauma, chronic ear disease or may occur spontaneously.

1. Infections. Viral infections are the well-documented cause. It may affect cochlea (viral endolymphatic labyrinthitis) or eighth cranial nerve (viral neuronitis). Meningococcal meningitis, Encephalitis, Herpes virus (simplex, zoster, varicella, cytomegalovirus), Mumps, Measles, Human immunodeficiency virus, Lyme disease, Rubella, Syphilis, Toxoplasmosis.
2. Vascular. Vasospasm, thrombosis, embolism of the labyrinthine or cochlear artery. Vasospasm (ie, arterial vasoconstriction) is often due to stress, fatigue, and the emotional state of the patient. Thrombosis and embolism are usually due to arteriosclerosis. Haemorrhage (leukaemia) into the inner ear. They may be associated with diabetes, hypertension, polycythaemia, macroglobinaemia or sickle cell trait.
3. Trauma. Noise trauma, barotrauma, head injury, ear operations (stapedectomy), spontaneous rupture of cochlear membranes (perilymph fistula).
4. Autoimmunity. Immune-mediated sensorineural hearing loss. Wegener’s granulomatosis, Rheumatoid arthritis, Sjogren’s syndrome, Polyarteritis nodosa, Relapsing polychondritis, Lupus erythematosus Ulcerative colitis, Autoimmune inner-ear disease (AIED), Cogan’s syndrome Antiphospholipid syndrome, Sarcoid.
5. Neoplastic. Acoustic neuroma. Metastases in the cerebellopontine angle, carcinomatous neuropathy, Leukaemia, Myeloma.
6. Ear (otologic). Meniere’s disease, Cogan’s syndrome, large vestibular aqueduct.
7. Toxic. Ototoxic drugs (Aminoglycoside antibiotics, Loop diuretics, NSAIDs, Salicylates), insecticides, platinum-based chemotherapeutic agents,  general anaesthesia
8. Miscellaneous. Multiple sclerosis, hypothyroidism, sarcoidosis.
9. Psychogenic.

Management of Sudden Sensorineural Hearing Loss

In the majority of cases, there is no cause present (idiopathic). Nonetheless, examination and investigation are important to exclude treatable causes.

1. Careful history and examination. Rule out possibilities such as middle ear infection or disease, viral endolymphatic labyrinthitis, ototoxicity, Meniere’s disease, trauma, bacterial labyrinthitis, and perilymph fistula, and elicit neurological signs if present.
2. Vestibular tests. It is important if vertigo and accompanying nystagmus are present. Fistula test, Fitzgerald-Hallpike caloric test with electronystagmographic monitoring.
3. Imaging studies of temporal bones. Magnetic resonance imaging (MRI) scanning to rule out acoustic neuroma, multiple sclerosis and cerebrovascular accidents. Fine-cut contrast CT of the temporal bone is advised if MRI is contraindicated.
4. Audiometry must be performed to know the degree and type of hearing loss. 30-35 dB or more of SNHL in at least three consecutive frequencies occurring over 72 hours or less strongly indicates SSNHL. BERA can also be done.
5. Blood tests for autoimmune disease, inflammatory markers and syphilis are required. Blood glucose level for diabetes.
6. Exploratory tympanotomy where perilymph fistula is strongly suspected.

Treatment:

First, treat the cause if any. Idiopathic sensorineural sudden hearing loss treatment is empirical and consists of:

1. Bed rest.
2. Steroid therapy. Prednisolone 40–60 mg (1 mg/kg/day, up to a maximum of 60 mg daily) in a single morning dose for 1 week and then tapered off in 3 weeks. Steroids are anti-inflammatory and relieve oedema. They have been found useful in idiopathic sudden hearing loss of moderate degree. The treatment is based on the maximum adrenal output of hydrocortisone (cortisol), which is 200–300 mg/day during stress.
3. Inhalation of carbogen (5% CO₂+ 95% O₂). It increases cochlear blood flow and improves oxygenation.
4. Vasodilator drugs.
5. Low molecular weight dextran. It decreases blood viscosity. It is contraindicated in cardiac failure and bleeding disorders.
6. Hyperbaric oxygen therapy. Hyperbaric oxygen therapy (HBOT) delivers 100% oxygen to a patient at a pressure greater than 1 atmosphere. This increases the concentration of oxygen in labyrinthine fluids and improves cochlear function. Therapy typically involves multiple sessions of 1–2 hours over days to weeks. HBOT is an expensive and time-consuming intervention that is available only in selected centres.
7. Low-salt diet and a diuretic. It is empirical and has the same benefit as in cases of meniere’s disease.
8. Intratympanic (IT) steroids therapy. It raises the local concentration of steroids in cochlear fluids, thus the main advantage of IT treatment is the reduction in systemic corticosteroid side effect. Dexamethasone and solumedrol (methylprednisolone sodium succinate) are the most commonly used IT steroids. Most studies quote doses of 10–24 mg/mL dexamethasone and 30–40 mg/mL solumedrol. Higher concentrations may have better outcomes. Adverse effects with IT steroids are infrequent but include pain, transient dizziness, infection, persistent tympanic membrane perforation, a possible vasovagal episode during injection, and the need for repeat visits. The main risk appears to be a persistent tympanic membrane perforation at the injection site.

———– End of the chapter ———–

Learning resources.

• Scott-Brown, Textbook of Otorhinolaryngology Head and Neck Surgery.
• Michael M Paparella, Textbook of Otolaryngology: Principles & Practice.
• Glasscock-Shambaugh, Textbook of  Surgery of the Ear.
• P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
• Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
• Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck surgery.
• Anirban Biswas, Textbook of Clinical Audio-vestibulometry.

Author:

Dr. Rahul Kumar Bagla
MS & Fellow Rhinoplasty & Facial Plastic Surgery.
Associate Professor & Head
GIMS, Greater Noida, India
msrahulbagla@gmail.com

 

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