What are the main causes of bilateral tinnitus in patients with normal hearing?

Main Causes of Bilateral Tinnitus with Normal Hearing

The main causes of bilateral tinnitus in patients with normal hearing include medications, noise-induced subclinical damage, metabolic disorders, autoimmune conditions, and psychogenic factors, with medications being the most common etiology that should be evaluated first. 1, 2

Etiology Classification

Common Causes

• Medication-induced tinnitus

  • Ototoxic medications (even without detectable hearing loss) 3
  • Common culprits include certain antibiotics, NSAIDs, and diuretics

• Noise exposure

  • Subclinical cochlear damage from noise exposure 2
  • May not be detectable on standard audiometry

• Metabolic disorders

  • Thyroid dysfunction
  • MELAS syndrome 3
  • Hyperlipidemia

Less Common Causes

• Autoimmune conditions

  • Autoimmune inner ear disease 3
  • Cogan syndrome 3

• Psychogenic factors

  • Depression
  • Anxiety disorders 4
  • Stress-related somatic manifestations

• Vascular abnormalities

  • Atherosclerosis of carotid arteries 5
  • Arteriovenous malformations (rare with normal hearing) 5

• Neurologic disorders

  • Auditory cortex dysfunction 2
  • Somatosensory system dysfunction 2

Diagnostic Approach

Initial Evaluation

1. Medication review

   • Identify and consider discontinuation of potentially ototoxic medications

2. History of noise exposure

   • Occupational exposure
   • Recreational exposure (concerts, headphone use)

3. Assessment for fluctuating symptoms

   • Fluctuating tinnitus suggests non-idiopathic causes such as autoimmune inner ear disease 3

Warning Signs Requiring Further Investigation

• Focal neurological symptoms
• Pulsatile quality to tinnitus
• Recent head trauma
• Concurrent vestibular symptoms

Imaging Considerations

According to the American College of Radiology guidelines, imaging is usually not appropriate for symmetric or bilateral subjective nonpulsatile tinnitus in the absence of other symptoms 1. However, imaging should be considered if there are:

• Neurological deficits
• Pulsatile quality to tinnitus
• Head trauma history
• Associated hearing loss

Management Approach

Since no effective drug treatments are available for most cases of tinnitus 4, management should focus on:

1. Addressing underlying causes

   • Modification of ototoxic medications
   • Management of metabolic disorders
   • Treatment of autoimmune conditions if identified

2. Symptomatic relief

   • Sound therapy (wide-band sound) 4
   • Counseling and cognitive behavioral therapy 4, 2
   • Auditory masking devices 5

Clinical Pearls and Pitfalls

• Pearl: Even with normal audiometry, subclinical hearing loss may be present and contribute to tinnitus 2
• Pitfall: Telling patients "nothing can be done" is inappropriate; multiple management strategies exist even when no specific cause is found 5
• Pearl: Bilateral tinnitus with normal hearing is rarely associated with serious intracranial pathology, unlike unilateral tinnitus which requires more thorough investigation 1, 6
• Pitfall: Failing to recognize that tinnitus may be an early symptom of a systemic condition before hearing loss develops

Remember that while most cases of bilateral tinnitus with normal hearing are benign, a thorough evaluation is essential to rule out treatable underlying causes and provide appropriate management for symptom relief.