Horizontal BPPV Nystagmus Direction
In horizontal (lateral canal) BPPV, the nystagmus is purely horizontal, not torsional. 1
Key Distinguishing Features
The hallmark of horizontal canal BPPV is horizontal direction-changing nystagmus that differs fundamentally from the torsional upbeating nystagmus seen in posterior canal BPPV. 2, 3
Two Distinct Patterns
Geotropic type (most common): Horizontal nystagmus beats toward the undermost (ground-facing) ear on both sides during the supine roll test, with more intense nystagmus when the affected ear is down 1, 4
Apogeotropic type (less common): Horizontal nystagmus beats toward the uppermost ear on both sides, with the direction reversing when the head is turned to the opposite side 1, 5
Clinical Diagnostic Algorithm
Perform the supine roll test when the Dix-Hallpike maneuver is negative but BPPV is suspected clinically. 1, 2
Supine Roll Test Technique:
- Position patient supine with head neutral 1
- Rapidly rotate head 90 degrees to one side and observe for horizontal nystagmus 1
- Return to neutral position after nystagmus subsides 1
- Rapidly rotate head 90 degrees to opposite side and observe again 1
Identifying the Affected Ear:
- Geotropic form: The side producing the most intense nystagmus is the affected ear 1, 2
- Apogeotropic form: The side opposite to the strongest nystagmus is the affected ear 2, 3
Critical Pitfalls to Avoid
Do not confuse horizontal canal BPPV with posterior canal BPPV—the nystagmus patterns are completely different. 2, 3
- Posterior canal BPPV produces torsional upbeating nystagmus during Dix-Hallpike testing 2, 3
- Horizontal canal BPPV produces purely horizontal nystagmus without significant torsional or vertical components during supine roll testing 1, 6
- Horizontal canal BPPV accounts for 10-15% of all BPPV cases and is frequently missed when clinicians only perform Dix-Hallpike testing 1, 2
Canal conversion can occur: Up to 6% of patients initially treated for one canal type may convert to another canal type, requiring reassessment with different positional testing 2, 3
CNS adaptation may cause spontaneous nystagmus direction changes without head repositioning, which can confuse diagnosis. 1, 2