Benign Paroxysmal Positional Vertigo (BPPV) is a frequent cause of vertigo, a sudden sensation of spinning that is triggered by changes in head position. This common inner ear disorder occurs when tiny calcium carbonate crystals, called otoconia, dislodge from their normal location in the utricle and migrate into one of the three fluid-filled semicircular canals. The vast majority of cases involve the posterior semicircular canal, which is diagnosed using the standard Dix-Hallpike test. However, a less common but significant variant is Horizontal Canal BPPV (HC-BPPV), which requires a specialized diagnostic approach. The standard Dix-Hallpike maneuver is ineffective for this variant because the head positions used do not adequately stimulate the horizontal canal.
Mechanical Differences of Horizontal Canal BPPV
The distinction in testing arises from the anatomy of the inner ear, as HC-BPPV involves the horizontal semicircular canal instead of the posterior one. This horizontal canal is positioned differently within the temporal bone, meaning head movements must be adjusted to align the canal with the plane of gravity. When otoconia enter this canal, they interfere with the normal fluid dynamics that sense head movement, sending false signals to the brain. The misplaced particles can present in two primary ways: canalithiasis, where otoconia are free-floating within the canal fluid (endolymph), and cupulolithiasis, where otoconia adhere to the cupula at the end of the canal. These different mechanical issues lead to distinct patterns of involuntary eye movement, or nystagmus, during the diagnostic test.
The Supine Roll Test Procedure
The specific diagnostic maneuver for HC-BPPV is the Supine Roll Test, also known as the Pagnini-McClure maneuver. The test begins with the patient lying face-up on an examination table, with their head slightly flexed forward by approximately 30 degrees. This forward tilt is important because it positions the horizontal semicircular canal into a vertical plane, making the free-floating debris sensitive to gravity.
The clinician rapidly turns the patient’s head 90 degrees to one side and maintains this position for about 30 seconds while observing the patient’s eyes for the onset, direction, and intensity of nystagmus and symptoms. The head is then returned to the neutral position to allow any nystagmus to subside. Next, the head is quickly turned 90 degrees to the opposite side, and the eyes are observed again for 30 seconds. The clinician must compare the intensity of vertigo and nystagmus when the head is turned to the right versus the left to identify the affected ear and the specific variant of HC-BPPV.
Observing Nystagmus Responses
A positive Supine Roll Test is characterized by the induction of horizontal nystagmus, an involuntary, rapid, side-to-side movement of the eyes. Unlike the posterior canal variant, which produces torsional and vertical nystagmus, HC-BPPV causes a purely horizontal eye beat. The positional change causes the movement of the otoconia, which drags the endolymph fluid and deflects the cupula, resulting in the eye movement. The crucial observation is that the nystagmus is “direction-changing,” meaning the fast phase beats toward one side when the head is turned right and toward the opposite side when the head is turned left. The test is considered positive if nystagmus is provoked on both sides, but it is typically more pronounced when the affected ear is placed downward.
Classifying Geotropic and Apogeotropic Variants
The final step in diagnosis involves classifying the nystagmus as either geotropic or apogeotropic, which correlates with the location of the debris in the canal. Geotropic nystagmus is defined by the fast phase of the eye beat moving toward the ground, or the lowermost ear. This pattern is most often indicative of canalithiasis, where free-floating otoconia are moving along the longer arm of the horizontal canal. For the geotropic type, the affected ear is the one that elicits the stronger and more intense nystagmus response.
The apogeotropic variant presents with the fast phase of the eye beat moving away from the ground, or toward the uppermost ear. This finding is typically attributed to otoconia adhering directly to the cupula (cupulolithiasis) or lodged in the shorter arm of the canal. In the apogeotropic form, the affected ear is paradoxically the one that elicits the weaker nystagmus response. Correctly identifying the specific variant and the affected ear is important because treatment, such as the Gufoni or Lempert roll maneuvers, must be tailored to the debris location for successful resolution.