Sudden onset hearing loss (SOHL)

• Sudden onset hearing loss (SOHL) is a subjective symptom in one or both ears, as perceived by the patient. To objectively determine whether there is a hearing loss, a pure tone audiogram (PTA) must be performed. A clinical assessment can differentiate between
  • Conductive hearing loss (CHL)
    • most common
  • Sensorineural hearing loss (SNHL).
• Sudden sensorineural hearing loss (SSNHL)
  • hearing loss of 30 dB or more over at least three contiguous frequencies
  • period of 72 hours or less.
  •  can range from mild hearing impairment to a total loss of hearing
  • may be temporary or permanent

• in the majority of cases of sudden sensorineural hearing loss (SSNHL), no cause is identified and it is considered idiopathic SSNHL.
  • In these patients, high dose oral prednisolone may improve hearing outcome, particularly if started early.
• Regardless of the cause and degree of hearing loss, rapid assessment and early treatment is vital

Aetiology of SOHL	clinical
Outer ear (conductive hearing loss)
Foreign body Wax Otitis externa Other ear canal pathology (eg. exostoses) Trauma (syringing)	Non-distorted sound Features of external ear pathology Volume of voice remains normal and hearing improves in noisy environment
Middle ear (conductive hearing loss)
Otitis media with effusion Haemotympanum Ossicular chain discontinuity Trauma Barotrauma Iatrogenic (post-operative) Tympanic membrane perforation Cholesteatoma
Inner ear (sensorineural hearing loss)
Idiopathic Noise Exposure: – Prolonged exposure to loud noises (e.g., machinery, music) causing damage to hair cells. Aging (Presbycusis): – Natural degeneration of the auditory system with age. Infective: – viral/bacterial ([HIV], [CMV], [HSV], mumps, rubella, syphilis) Trauma (temporal bone fracture) Ototoxic drugs (e.g., aminoglycoside antibiotics, chemotherapy agents) Autoimmune – SLE – Wegener – Cogan syndrome – relapsing polychondritis – ulcerative colitis Tumour – vestibular schwannoma – leukaemia – myeloma Vascular (cerebrovascular disease, sickle cell disease) Perilymphatic fistula Barotrauma Neurological – multiple sclerosis – cerebrovascular accident – migraine) Other (diabetes mellitus, sarcoidosis)Non-organic hearing loss	Distorted sound +/- tinnitusNo features of external ear pathology Volume of voice is loud, hearing worsens in noisy environment and high frequencies lost preferentially

Red flags associated with SOHL

Unilateral Hearing Loss: Sudden loss of hearing in one ear, which can indicate serious conditions such as acoustic neuroma or stroke. Associated Neurological Symptoms: Vertigo: Sudden onset of severe dizziness or spinning sensation. Facial Weakness: Indicates potential cranial nerve involvement, possibly from a stroke or tumor. Severe Headache: Could be indicative of a cerebrovascular event or a space-occupying lesion. Diplopia (Double Vision): Suggests a possible central nervous system pathology. Recent Trauma: Head Trauma: Recent injury to the head can cause perilymph fistula or temporal bone fracture. Barotrauma: Sudden changes in pressure (e.g., diving, flying). Otologic Symptoms: Otorrhea (Ear Discharge): Suggests possible infection, such as otitis media or cholesteatoma. Ear Pain: Severe pain may indicate an infection or inflammatory process. Tinnitus: Sudden onset of ringing in the ears, especially if unilateral. Infectious Symptoms: Fever: Suggestive of systemic infection or meningitis. Recent Upper Respiratory Infection: Could be associated with viral labyrinthitis. History of Otologic Disease: Chronic Ear Infections: Increased risk for complications like cholesteatoma. Previous Ear Surgery: Could indicate complications or recurrent disease. Systemic Symptoms: Rash: Especially vesicular rashes that may suggest herpes zoster oticus (Ramsay Hunt syndrome). Weight Loss/Night Sweats: Possible indication of malignancy or chronic infection. Medication Use: Ototoxic Drugs: Recent use of medications known to be ototoxic (e.g., aminoglycosides, cisplatin). Autoimmune Conditions: Sudden Bilateral Hearing Loss: May indicate an autoimmune inner ear disease. Family History: Familial history of hearing loss or genetic syndromes affecting hearing.

History

• Which ear
  • unilateral or bilateral (rare, caused by autoimmune disease, syphilis, trauma, neoplasia and vascular causes)
• Sudden or Gradual
  • gradual loss may be associated with a pre-existing disorder, such as Ménière’s disease.
• Water may precipitate wax impaction. 
• Trauma (physical or acoustic/ Excess noise exposure ) can result in
  • ossicular discontinuity (CHL), or SNHL in cases of extreme noise exposure or brain damage. 
• Excessive straining
  • Cause perilymph fistula
  • tinnitus and vertigo would also usually be present 
• Tinnitus and dizziness
  • non-specific and may not help to differentiate between CHL and SNHL
• Coryzal symptoms, fever, discharge, otalgia or recurrent ear infections with foul smelling discharge all provide clues to the aetiology of the hearing loss.
• The patient’s PMHx:
  • autoimmune disease
  • diabetes mellitus
  • sarcoidosis
  • vascular disease
• ototoxic drugs
  • aminoglycosides, frusemide, NSAIDs, chemotherapeutic agents (cisplatinum), quinine and salicylates at high doses. 

Examination

•  head and neck and regional lymph nodes.
• Lymphadenopathy
  • may indicate
    • malignancy
  •   middle ear infection affecting the facial nerve
• Cranial nerve abnormalities
  • intracranial lesions (such as acoustic neuromas or malignancy)
  • multiple sclerosis. 
• Otitis externa
  • discharge at the external meatus or pain on moving the pinna. 
• Mastoiditis
  • mastoid tenderness or fluctuance.

• Otoscopy
  • Check for
    • Foreign bodies
    • Wax
    • Discharge
    • masses. 
  • tympanic membrane perforation especially if there is a history of trauma or infection.

Tuning fork tests

• The 512 Hz tuning fork is commonly used in clinical practice to assess hearing because it provides reliable results for both bone and air conduction tests. Below is a summary of how to perform and interpret Rinne’s and Weber’s tests.
• Rinne’s Test
  • Procedure:
    • Place a vibrating 512 Hz tuning fork firmly on the mastoid process to test bone conduction. Ensure firm contact by applying pressure to the opposite side of the head.
    • Ask the patient to indicate when they can no longer hear the sound.
    • Move the tuning fork in front of the external auditory meatus to test air conduction.
    • Ask the patient if they can hear the sound again.
  • Interpretation:
    • Normal Hearing (Rinne’s Positive):
      • Air conduction (AC) is better than bone conduction (BC).
      • The patient hears the sound when the tuning fork is moved in front of the ear after it can no longer be heard on the mastoid.
    • Conductive Hearing Loss (Rinne’s Negative):
      • Bone conduction (BC) is better than air conduction (AC).
      • The patient hears the tuning fork longer on the mastoid than in front of the ear.
    • Sensorineural Hearing Loss:
      • Rinne’s test remains positive (AC > BC), but the patient may have a ‘false negative’ if they cannot hear anything in the affected ear; bone vibrations might be transmitted to the unaffected ear.
• Weber’s Test
  • Procedure:
    • Tap a 512 Hz tuning fork and place it in the midline of the forehead.
    • Ask the patient “Where do you hear the sound?”
  • Interpretation:
    • Normal Hearing:
      • Sound is heard equally in both ears (midline).
    • Conductive Hearing Loss:
      • Sound localizes to the affected ear.
      • The affected ear has less environmental noise and low-frequency sounds are trapped within the inner ear, increasing loudness.
    • Sensorineural Hearing Loss:
      • Sound localizes to the unaffected ear.
• Additional Notes
  • The 512 Hz tuning fork is preferred due to its balance between decay time and minimizing tactile vibration.
  • Rinne’s Test Sensitivity: While useful, it has low sensitivity, and results should be interpreted in conjunction with other clinical findings.
  • Demonstration of Conductive Loss: Speaking or humming and then occluding one ear can illustrate how conductive loss causes increased loudness in the occluded ear.

	Rinne’s test	Weber’s test
Normal	Air conduction > bone conduction  (Positive Rinne’s)	Heard in the midline
Conductive hearing loss	Bone conduction > Air conduction (Negative Rinne’s)	Heard in the bad ear
Sensorineural hearing loss	Air conduction > bone conduction (Positive Rinne’s)	Heard in the good ear

Free field testing 

• sensitivity of 90–100%
• specificity of 70–87%
• The examiner tests the patient’s hearing with whispered, conversational and loud voice (indicating higher sound thresholds) while standing 60 cm behind the seated patient. If responses are poor, then the test can be repeated at 15 cm from the patient. Free field testing does not differentiate the type of hearing loss, but can be useful in the consulting room where audiology is not available.

Investigations

Pure tone audiogram

• initial audiological test used to distinguish CHL from SNHL
• Understanding the Audiogram Layout
  • Axes:
    • Horizontal Axis (X-Axis): Represents the frequency (pitch) of sounds, measured in Hertz (Hz). It typically ranges from 250 Hz to 8000 Hz.
    • Vertical Axis (Y-Axis): Represents the hearing threshold level, measured in decibels (dB). It usually ranges from -10 dB to 120 dB. The higher the number, the louder the sound.
  • Symbols:
    • Right Ear: Represented by a red “O”.
    • Left Ear: Represented by a blue “X”.
    • Bone Conduction Right Ear: Typically represented by a red “<“.
    • Bone Conduction Left Ear: Typically represented by a blue “>”.
• Interpreting the Results
  • Thresholds:
    • The points marked on the graph where the person begins to hear the sound at various frequencies. The lower the mark on the audiogram, the better the hearing at that frequency.
  • Hearing Levels:
    • Normal Hearing: -10 to 20 dB
    • Mild Hearing Loss: 21 to 40 dB
    • Moderate Hearing Loss: 41 to 55 dB
    • Moderately Severe Hearing Loss: 56 to 70 dB
    • Severe Hearing Loss: 71 to 90 dB
    • Profound Hearing Loss: 91+ dB
  • Shape of the Audiogram:
    • Flat: Similar loss across all frequencies.
    • Sloping: Better hearing at low frequencies, worse at high frequencies.
    • Rising: Worse hearing at low frequencies, better at high frequencies.
    • Notched: A significant dip at certain frequencies (often seen in noise-induced hearing loss).
• Steps to Read an Audiogram
  • Identify the Symbols:
    • Red: Right ear results.
    • Blue: Left ear results.
    • Bone conduction thresholds: Represented by symbols such as < and >.
    • Air conduction thresholds: Represented by symbols such as O (right ear) and X (left ear).
  • Examine the Frequency (X-Axis):
    • Start from the left (low frequencies) and move to the right (high frequencies).
  • Check the Hearing Thresholds (Y-Axis):
    • Note the dB level at which the person starts to hear each frequency.
    • The marks closer to the top of the graph indicate better hearing.
  • Assess the Hearing Loss Type:
    • Conductive Hearing Loss:
      • bone conduction thresholds are 15 dB or better than air conduction thresholds
      • bone conduction thresholds are 15 dB or less.
    • Sensorineural Hearing Loss:
      • if the difference between air conduction (AC) and bone conduction (BC) thresholds is less than 15 dB
      • both thresholds are worse than 15 dB
    • Mixed Hearing Loss: Combination of both conductive and sensorineural loss.
  • Look for Patterns:
    • Note any specific patterns like notching, which could indicate noise-induced hearing loss.
  • Example of Reading an Audiogram
    • Normal Hearing: Thresholds at or above 20 dB across all frequencies.
    • Noise-Induced Hearing Loss: Notching pattern at 4000 Hz, indicating a dip in hearing sensitivity typical of exposure to loud sounds

• Tympanometry
  • assesses tympanic membrane mobility and middle ear function. 
  • Fluid in the middle ear is represented as a ‘flat’ trace (type B tympanogram), and is consistent with CHL.
• Flexible nasoendoscopy
• Blood tests
  • Full blood count
  • Erythrocyte sedimentation rate (ESR)
  • Urea and electrolytes        
  • Fasting blood glucose
  • Fasting cholesterol/triglycerides
  • Viral titres (HIV, CMV, HSV, mumps, rubella)
  • FTA-abs for syphilis (or VDRL)
  • Lyme titres (this is rare and could be considered in patients returning from endemic areas)
  • Thyroid function tests/anti-thyroid antibodies
  • Angiotensin-converting enzyme (ACE)
  • Anti-neutrophil cytoplasmic antibodies (ANCA)
  • Antinuclear antibodies (ANA)
  • Rheumatoid factor (RF)
  • Anti-cyclic citrullinated peptide (anti-CPP)
  • Anti-phospholipid antibodies

Imaging

• MRI
  • Suspect vestibular schwannoma : if unilateral or asymmetrical SNHL (>15 dB)
  • demyelination, typically seen in multiple sclerosis, and small vessel ischaemic changes.
• CT
  • can exclude large acoustic neuromas in SNHL
  • evaluate the middle ear/ossicular chain in conductive hearing loss. 
• chest X-ray
  • suspicion of sarcoidosis with mediastinal involvement.

Management

• Conductive hearing loss
  • Manage wax, foreign bodies or otitis externa,Acute otitis media 
• Tympanic membrane perforations
  • usually heal spontaneously within a few days to weeks. 
  • Topical antibiotics are not routinely required unless there is an associated infection.
  • Referral to an ENT surgeon for consideration of repair (tympanoplasty) may be required should the perforation not heal.