How do you differentiate between posterior canal Benign Paroxysmal Positional Vertigo (BPPV) and lateral canal BPPV?

Differentiating Posterior Canal BPPV from Lateral Canal BPPV

Use the Dix-Hallpike maneuver to diagnose posterior canal BPPV and the supine roll test to diagnose lateral canal BPPV—the distinct nystagmus patterns (torsional upbeating versus horizontal) and diagnostic maneuvers definitively distinguish these two entities. 1

Diagnostic Maneuvers

For Posterior Canal BPPV

• Perform the Dix-Hallpike maneuver by rapidly moving the patient from sitting to supine with the head extended 20 degrees and turned 45 degrees to one side 1
• The test has 82% sensitivity and 71% specificity for posterior canal BPPV 1
• A positive test produces torsional, upbeating nystagmus with a latency period of 5-20 seconds, with both nystagmus and vertigo resolving within 60 seconds 1
• The affected ear is the one facing downward during the positive Dix-Hallpike maneuver 1
• Posterior canal BPPV accounts for 85-95% of all BPPV cases 2, 3

For Lateral Canal BPPV

• Perform the supine roll test when the Dix-Hallpike is negative but clinical suspicion for BPPV remains high 4
• Position the patient supine with head neutral, then quickly rotate the head 90 degrees to one side, observe for nystagmus, return to neutral, then rotate 90 degrees to the opposite side 4
• Lateral canal BPPV accounts for 10-15% of BPPV cases 4, 3

Nystagmus Patterns: The Key Differentiator

Posterior Canal BPPV

• Torsional, upbeating nystagmus is the hallmark finding 1
• The torsional component beats toward the affected ear 5
• Nystagmus has a characteristic latency and fatigability 1

Lateral Canal BPPV: Two Variants

• Geotropic type (most common): Horizontal nystagmus beating toward the undermost ear on both sides of head rotation, with more intense nystagmus when the affected ear is down 4
• Apogeotropic type (less common): Horizontal nystagmus beating toward the uppermost ear on both sides, with the affected ear being opposite to the side producing stronger nystagmus 4, 1
• The geotropic variant predominates in lateral canal BPPV 4
• In geotropic lateral canal BPPV, 30 out of 37 cases (81%) showed geotropic nystagmus versus 7 cases with apogeotropic nystagmus 3

Clinical Algorithm

1. Start with Dix-Hallpike maneuver on both sides for all patients with positional vertigo 1

   • If torsional upbeating nystagmus → Posterior canal BPPV
   • If negative → Proceed to step 2

2. Perform supine roll test when Dix-Hallpike is negative but history suggests BPPV 4

   • If horizontal nystagmus → Lateral canal BPPV
   • Determine geotropic versus apogeotropic variant by nystagmus direction

3. Identify the affected side by comparing nystagmus intensity 4, 1

   • Geotropic: Side with stronger nystagmus = affected ear
   • Apogeotropic: Side opposite to stronger nystagmus = affected ear

Critical Pitfalls to Avoid

• Do not skip the supine roll test in patients with negative Dix-Hallpike but classic BPPV history—lateral canal BPPV is frequently missed because clinicians are unaware of this diagnostic maneuver 4
• Watch for "canal switch": Lateral canal BPPV commonly occurs after performing Epley maneuver for posterior canal BPPV as otoconia migrate from posterior to lateral canal 4
• Presenting symptoms are often indistinguishable between posterior and lateral canal BPPV—you cannot differentiate based on history alone 4
• Suppress visual fixation during examination to properly observe nystagmus patterns, as visual fixation can mask the findings 6
• CNS adaptation may cause spontaneous nystagmus direction change without rolling to the opposite ear, which can confuse diagnosis 4
• Horizontal nystagmus can indicate central pathology—if lateral canal BPPV is suspected, ensure no other neurological abnormalities are present before proceeding with treatment 7