How can central hearing loss be distinguished from peripheral hearing loss?

Differentiating Central from Peripheral Hearing Loss

Use tuning fork tests (Weber and Rinne) combined with audiometry to distinguish conductive from sensorineural hearing loss, then identify central causes by looking for focal neurologic signs, bilateral involvement, abnormal speech discrimination disproportionate to pure-tone loss, and retrocochlear findings on MRI or auditory brainstem response testing. 1

Initial Bedside Differentiation: Peripheral vs Central Localization

Step 1: Distinguish Conductive from Sensorineural Loss

Tuning Fork Testing (256 or 512 Hz):

• Weber test: Strike the fork on a covered elbow/knee and place at forehead midline 1

  • Sound lateralizes to the affected ear = conductive hearing loss 1
  • Sound lateralizes to the better ear = sensorineural hearing loss 1

• Rinne test: Place vibrating fork on mastoid, then at ear canal entrance 1

  • Bone conduction > air conduction (negative Rinne) = conductive loss 1
  • Air conduction > bone conduction (positive Rinne) in both ears = sensorineural loss 1

Critical caveat: Remove impacted cerumen before testing, as it causes conductive loss that confounds results 1, 2

Step 2: Confirm with Formal Audiometry

• Pure-tone audiometry with air and bone conduction is mandatory within 14 days to definitively establish sensorineural hearing loss 2
• An air-bone gap ≥15-20 dB confirms conductive loss 1
• Sensorineural loss shows elevated air and bone thresholds with minimal gap 3

Distinguishing Peripheral (Cochlear) from Central (Retrocochlear/Brainstem/Cortical) Causes

Red Flags for Central Pathology

Clinical features suggesting non-peripheral causes:

• Bilateral sudden hearing loss – suggests autoimmune, infectious, toxic, or central etiologies rather than typical idiopathic peripheral loss 3, 2, 4
• Focal neurologic symptoms: headache, confusion, diplopia, dysarthria, focal weakness, facial weakness, ataxia, vertigo with nystagmus (especially gaze-evoked or downbeat) 3
• Recurrent or fluctuating hearing loss – consider Ménière's disease, autoimmune inner ear disease, or Cogan's syndrome 3
• History of recent head trauma, acoustic trauma, or barotrauma 3
• Associated symptoms: severe bilateral vestibular loss with oscillopsia, concurrent eye symptoms (pain, redness, photophobia) 3

Mandatory Workup for Retrocochlear/Central Pathology

All patients with confirmed sensorineural hearing loss require evaluation for retrocochlear pathology:

• MRI with gadolinium (dedicated internal auditory canal protocol) is the gold standard for detecting acoustic neuromas, cerebellopontine angle lesions, brainstem infarcts, and meningeal enhancement 2, 4
• Auditory brainstem response (ABR) testing can identify retrocochlear dysfunction when MRI is contraindicated 2
• Do NOT order routine head CT – it has poor sensitivity for early brainstem infarcts and retrocochlear lesions 3, 4

Specific Central vs Peripheral Patterns

Peripheral (cochlear) hearing loss characteristics:

• Unilateral presentation is typical for idiopathic sudden sensorineural hearing loss 3
• Normal otoscopic exam 1
• May have tinnitus and/or vertigo, but no focal neurologic signs 3
• Speech discrimination scores proportionate to pure-tone thresholds 5

Central (retrocochlear/brainstem) hearing loss characteristics:

• Disproportionately poor speech discrimination relative to pure-tone loss 5
• Abnormal ABR with prolonged or absent wave latencies 2
• Focal neurologic findings on examination 3
• MRI abnormalities: vestibular schwannoma, brainstem lesions, white matter changes, meningeal enhancement 3, 4
• Sound localization deficits suggest central auditory pathway involvement 5

Algorithmic Approach

1. Perform tuning fork tests to distinguish conductive from sensorineural loss 1
2. Obtain formal audiometry within 14 days with air/bone conduction 2
3. Screen for central red flags: bilateral loss, focal neurologic signs, recurrent episodes 3, 2
4. Order MRI with gadolinium (IAC protocol) for all confirmed sensorineural hearing loss to exclude retrocochlear pathology 2, 4
5. If bilateral sudden loss: aggressive workup including comprehensive labs (syphilis, HIV, autoimmune panel, inflammatory markers), consider lumbar puncture if meningitis suspected 4

Common Pitfalls

• Never assume peripheral loss without audiometric confirmation – misdiagnosing central pathology as peripheral delays critical treatment 1, 2
• Tuning fork tests have limited sensitivity for mild losses and cannot replace formal audiometry 1
• Isolated eighth nerve involvement from multiple sclerosis is extremely rare (<1%), so consider other causes first 3
• Stroke rarely presents as isolated sudden hearing loss – peripheral vestibular involvement is usually present with brainstem infarcts 3