Benign Paroxysmal Positional Vertigo (BPPV) is a common inner ear disorder that causes sudden, brief episodes of spinning dizziness, typically triggered by changes in head position. BPPV occurs when tiny calcium carbonate crystals (otoconia) dislodge and migrate into one of the three semicircular canals. While the posterior canal is most frequently affected, the horizontal (or lateral) semicircular canal is involved in about 5 to 20% of all BPPV cases. This horizontal variant requires a completely different diagnostic approach than the one used for the more common posterior canal BPPV.
Why Horizontal Canal BPPV Requires Unique Testing
The anatomy of the horizontal semicircular canal necessitates a specialized test. The posterior canal is oriented vertically, allowing debris to be affected by gravity during the standard Dix-Hallpike maneuver. The horizontal canal, however, is oriented almost parallel to the ground when a person is standing upright.
When a patient is lying on their back, the horizontal canal sits in a near-vertical plane, making it highly sensitive to rotational movements. The standard diagnostic test for posterior canal BPPV is ineffective because it does not maximize the gravitational pull on the debris. Therefore, a dedicated positional maneuver is required to move the debris within the horizontal canal, causing the fluid inside to shift and trigger the characteristic symptoms. This specialized procedure is known as the Supine Roll Test.
The Supine Roll Test Procedure
The Supine Roll Test, also referred to as the Pagnini-McClure maneuver, is the standard method for diagnosing horizontal canal BPPV. The procedure begins with the patient lying face-up on an examination table, with the head elevated 20 to 30 degrees. This elevation aligns the horizontal semicircular canal vertically, positioning it in the plane of gravity’s pull.
From this starting position, the clinician quickly rotates the patient’s head 90 degrees to one side, holding the position for at least 30 seconds or until any involuntary eye movements subside. The patient’s eyes are observed closely during this rotation for the presence, direction, and duration of nystagmus, which is the involuntary, rhythmic movement of the eyes. The patient is then returned to the central, face-up position before the head is quickly turned 90 degrees to the opposite side, and the observation process is repeated.
The key diagnostic information comes from comparing the intensity and direction of the horizontal nystagmus between the rotation to the right and the rotation to the left. While the test is being performed, the clinician notes the latency, or the delay before the onset of the eye movement, and how long the nystagmus persists.
Interpreting Nystagmus Patterns
The nystagmus observed during the Supine Roll Test is purely horizontal. The direction of the nystagmus, relative to the ground, is the primary factor in determining the specific type of horizontal canal BPPV. The two main patterns are geotropic and ageotropic nystagmus.
Geotropic nystagmus beats toward the ground on both sides of the test and indicates canalithiasis, where the debris is free-floating in the long arm of the canal. The affected side is identified as the side that produces the stronger and more prolonged nystagmus and symptoms. This stronger response occurs because turning the head to the affected side causes the debris to move toward the inner ear’s sensory receptor, resulting in an excitatory movement.
Ageotropic nystagmus beats away from the ground on both sides of the test and suggests cupulolithiasis, where the debris is stuck to the sensory receptor itself. For this presentation, the affected side is usually the one that produces the weaker nystagmus, which is a reversal of the rule for geotropic nystagmus. If the nystagmus responses are similar in strength on both sides, a clinician may perform the Bow and Lean Test as a secondary measure to confirm the affected ear.