Sudden Sensorineural Hearing Loss: Causes and Evaluation

Sudden Sensorineural Hearing Loss (SSNHL) is defined as a hearing reduction greater than 30 db, over at least 3 consecutive frequencies (on pure tone audiogram), occurring over or less than 3 days. It usually affects one ear, there may be mild to sever reduction of hearing, and there may be tinnitus and dizziness.

Most People (30-65%) may have a spontaneous recovery; others may have permanent hearing difficulties.

Causes of sudden sensorineural hearing loss-

There is no conclusive evidence as why it happens but some theories are suggested-

1. Generally 90% cases are idiopathic where cause is not known. Viral diseases appears to be most common cause (about 60% cases) as shown by association with herpes.

2. There may be partial or complete blockage of circulation or vascular spasm to inner ear and nerves of hearing.

3. There may be rupture of delicate inner ear membrane after strong physical activity or sudden change in barometric pressure (flying/scuba diving).

4. Immune theory may ply a role, because of its association with Cogan syndrome, SLE, Lupus and AIDS.

In most cases reason remains unclear.

Diagnosis of SSNHL requires thorough investigation to determine any known causes of sudden hearing loss. Some of the causes are following-

* CONGENITAL –

  • Rubella Syndrome
  • Atresia of the External ear canal
  • Congenital Cytomegalovirus
  • Congenital Perilymphatic Fistula
  • Fetal Methyl Mercury Effects
  • Fetal Iodine Deficiency Effects

* MEDICATIONS (Ototoxic Drugs)-

  • Aminoglycoside Antibiotics-streptomycin, kanamyin, neomycin, amikacin, gentamicin, tobramicin and netilmicin
  • Loop diuretics, ethacrynic acid
  • Antimalarial (quinine, chloroquine),
  • Salicylates
  • NSAIDS
  • Vancomycin
  • Erythromycin
  • Cisplatinum

* INFECTIOUS DISEASES-

Bacterial infection:

  • Otitis media
  • Labyrinthitis
  • Encephalitis
  • Meningitis

Viral infections:

Evidence is circumstantial, with the possible exception of mumps parortitis and herpes zoster, the clinical diagnosis of viral infection is unreliable.

  • Common Colds
  • Adenovirus
  • Cytomegalovirus (Cmv)
  • Infectious Mononucleosis
  • Influenza
  • Parainfluenza
  • Ear Infection (Otitis Media)
  • Mumps
  • Measles
  • Rubella
  • Herpes Simplex Virus Type 1

Others:

Rocky Mountain spotted fever-tick borne infection

Lyme disease- tickborne especially in endemic areas (mostly causes facial palsy)

Syphilis and AIDS

* IMMUNOLOGIC DISEASES-

Immunologic activity within the cochlea may be the cause as suggested by finding of antibodies and response to steroid therapy in many patients. Hearing loss in certain autoimmune diseases is documented.

  • Cogan’s Syndrome
  • Systemic Lupus erythomatosus
  • Fibromyalgia
  • Temporal arteritis

* TRAUMATIC-

Direct trauma (temporal bone fracture) or blunt head injury (concussion to labyrinth) can cause SSNHL.

  • Traumatic ear drum Perforation
  • Head Injuries
  • Skull Fracture (Temporal Bone)

* ACOUSTIC TRAUMA

  • Explosions
  • Fireworks,
  • Gunfire
  • Rock Concerts/Mp3 Players
  • Jets
  • Occupational Work Noise

* BAROTRAUMA and perilymphatic fistula

Barotraumas is caused by unequalized pressure differentials in middle ear and external ear such as in scuba diving, air travellingor blow to ear. If the pressure is severe, eardrum can rupture.

Barotrauma can cause acquired perilymphatic fistula (communication between inner ear and middle ear) leading to SSNHL and vertigo. Other causes of acquired perilymphatic fistula are direct or indirect trauma to temporal bone, heavy lifting or straining and complication of stapes surgery.

* TUMORS-

  • Acoustic Neuroma or Vestibular Schwannoma – SSNHL may be initial manifestation
  • Temporal Bone Metastases
  • Neoplasm of CPA or IAC

* OTHER SYSTEMIC DISEASES-

  • Leukemia
  • Diabetes
  • Hypothyroidism
  • Multiple Sclerosis
  • Ménière’s Disease
  • Syphilis

Evaluation  of sudden sensorineural Hearing loss (searching for cause)-

A thorough and detailed history of associated symptoms, noise exposure, any trauma, fever, medication and family history of hearing loss is necessary to determine the diagnosis.

Ear examination by otoscopy and pneumotoscopy is critical step.

Hearing assessment by Tunning fork test, pure tone audiometry (PTA) and speech audiometry should be done. Tympanometry, Auditory Brainstem Response and Otoacoustic emission may be useful.

Electronystagmogram (ENG)

Radiologic study should be done especially for patients with unilateral sensorineural hearing loss, such as MRI with gadolinium/CT temporal bone to investigate IAC/CPA tumors.

Laboratory investigations-

FTA-antibodies for syphilis

ANA, RA Factor, ESR for autoimmune disease

Coagulation profile

CBC for infection

TH for thyroid function

RBS/PPBS for Diabetes

Cholesterol/triglycerides for hyperlipidemia

Sudden Sensorineural hearing loss-

  • It should be regarded as an otologic emergency.
  • Patient should be evaluated by otolaryngologist.
  • A thorough history, physical examination, appropriate laboratory and radiologic investigations including gadolinium enhanced MRI, and Audiometry tests should be carried out to find out known cause.

Next Post– Management of sudden sensorineural hearing loss

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