What are the causes of sudden hearing loss?

Causes of Sudden Hearing Loss

The majority of sudden hearing loss cases (90%) are idiopathic, with the most concerning non-idiopathic causes being vestibular schwannoma (acoustic neuroma), stroke, and malignancy. 1

Types of Sudden Hearing Loss

• Sudden hearing loss is defined as a rapid onset, occurring over a 72-hour period, of a subjective sensation of hearing impairment in one or both ears 1
• It can be classified as:
  • Conductive hearing loss - involving the ear canal, tympanic membrane, or middle ear 1
  • Sensorineural hearing loss - involving the cochlea, auditory nerve, or central auditory processing 1
  • Mixed hearing loss - combination of both types 1

Causes of Sudden Sensorineural Hearing Loss (SSNHL)

Idiopathic Causes (90% of cases)

• In most cases (85-90%), no specific cause can be identified at the time of presentation despite thorough evaluation 1
• Presumptively attributed to:
  • Vascular etiologies 1
  • Viral infections 1
  • Multiple or combined etiologies 1

Identifiable Causes (10-15% of cases)

Vascular Disorders

• Stroke affecting the auditory pathways 1
• Vascular occlusion or ischemia of the cochlea 2
• Migraine-associated vasospasm of cochlear vasculature 3

Infectious Causes

• Viral infections (proposed but often not confirmed) 2
• COVID-19 infection (emerging evidence) 4

Neoplastic Causes

• Vestibular schwannoma (acoustic neuroma) 1
• Other malignancies affecting the auditory pathway 1

Autoimmune Disorders

• Various autoimmune diseases affecting the inner ear 5

Other Causes

• Traumatic (head injury, barotrauma) 5
• Toxins and ototoxic medications 5
• Metabolic disorders 5
• Neurological disorders 5

Clinical Considerations

• Emergency intervention may be needed for rare, life-threatening conditions presenting with SSNHL 1
• In up to one-third of cases, the cause may only be identified during long-term follow-up 1
• Prognosis for recovery depends on several factors:
  • Patient age 1
  • Presence of vertigo at onset 1
  • Degree of hearing loss 1
  • Audiometric configuration 1
  • Time between onset and treatment 1

Diagnostic Approach

• Initial evaluation should distinguish between conductive and sensorineural hearing loss 1
• Audiometric testing is essential to confirm SSNHL (defined as ≥30 dB hearing loss at 3 consecutive frequencies) 1
• Patients should be assessed for bilateral hearing loss, recurrent episodes, or focal neurologic findings 1
• MRI, auditory brainstem response, or audiometric follow-up is recommended to evaluate for retrocochlear pathology 1

Treatment Considerations

• A maximum of 32-65% of SSNHL cases may recover spontaneously 1
• Early intervention may improve hearing recovery and quality of life 1
• Corticosteroids (systemic or intratympanic) are commonly used as initial therapy 1
• Long-term follow-up is important as some patients will have an underlying cause identified later 1

Pitfalls to Avoid

• Delaying diagnosis and treatment - prompt recognition and management may improve outcomes 1
• Missing life-threatening causes - thorough evaluation is needed to exclude serious conditions 1
• Inadequate follow-up - patients with partial or no recovery require ongoing management 1
• Overlooking SSNHL in intensive care settings - can be easily missed in critically ill patients 4