Clinical Manifestations of Benign Paroxysmal Positional Vertigo of the Horizontal Semicircular Canal: Pathophysiology of Atypical Manifestations

Pathophysiology of HSC

In the last years, causes other than the classic one described by ICVD of HSC-BPPV have been reported and may be observed in ordinary clinical examinations according to different eye movement presentations (nystagmus) by means of simple Frenzel glasses. These atypical presentations may be explained by pathophysiological disorders that affect the integrity (density or jamming) of the HSC lumen. These atypical clinical presentations may be classified as: heavy cupula, light cupula, partial jamming (plugging) and complete jamming of the HSC lumen [4, 5, 6, 7]. In this section, we will make a clinical description of the observed nystagmus in the examination setting, followed by its pathophysiological explanation.

When the head roll test elicits a DCPN, characterized by no latency and lasting more than one minute, which is defined as persistent, the first step is to determine which ear has the disorder. To do this, we must perform the “bow and lean test”, that consists on bringing the head forward and, after at least 3 minutes, bringing it back. The clinical interpretation is as follows: When the head roll test has shown a geotropic DCPN, the nystagmus in the bow and lean test beats in the direction of the affected ear when the patient keeps his head forward. Conversely, if the nystagmus has been apogeotropic, then the affected ear will be that of the direction of the nystagmus in the head-back position [4, 5, 8].

Once a supine head roll test elicits a “persistent” geotropic DCPN and the affected ear is determined by the bow and lean test, a light cupula phenomenon must be suspected, and the null plane (point test) in supine position is useful to diagnose it. This test consists of slowly turning the head 20-30º to the unaffected side, in which the persistent DCPN stops. The light cupula phenomenon has been classically described in positional alcohol nystagmus and, it has recently been postulated that the presence of proteoglycans adhered to the cupula generate a “float effect” that makes the cupula lighter, the sulfated proteoglycans are synthesized and secreted in the own cupula. Moreover, it has been proposed on the assumption that the specific gravity of the endolymph may increase due to a hemorrhage, inner ear hypoperfusion or inflammation, and in general by an over-compensation of the endolymphatic homeostasis [4, 5].

On the other hand, when a persistent apogeotropic nystagmus is observed in the head roll test, and the null plane is achieved by turning 20-30º towards the side of the affected ear, then a heavy cupula phenomenon must be suspected. Heavy cupula theory is controversial, and has classically been related to ingestion of heavy water. The apogeotropic DCPN is thought to be caused by detached otoconia rather than by an increased specific gravity of the endolymph or even a canalithiasis that fills the interior of the HSC. This theory may explain why particle repositioning maneuvers are more successful in heavy cupula than in light cupula phenomenon. Furthermore, the transition of apogeotropic to a geotropic nystagmus has been described in heavy cupula phenomenon; this clinical finding may be explained more likely by detached otoconia than specific gravity of the endolymph [4, 5] (Table 1).

Another atypical form of presentation of HSC-BPPV, frequently as a complication of performing particle repositioning maneuvers to treat any sort of BPPV, is a persistent vertigo associated with spontaneous horizontal fixed-direction nystagmus. It is usually accompanied by a hypoexcitability of the horizontal semicircular canal in caloric test, and a head impulse test showing a saccadic eye movement to the opposite side of the direction of horizontal fixed-direction nystagmus is generally observed in the setting of examination. In this case, a complete obstruction The pathophysiological mechanism is a complete plugging of the HSC that may generate a negative pressure inside the HSC in the same way a plunger would when positional tests are performed.

HSC-BPPV: Benign Paroxysmal Positional Vertigo of the horizontal semicircular canal DCPN: Direction Changing Positional Nystagmus HIT: Head Impulse Test HSN: Head Shaking Nystagmus hSN: horizontal Spontaneous Nystagmus On the other hand, when particle repositioning maneuvers were previously performed, and a fixed irritative horizontal positional nystagmus is elicited after positional tests, then the plugging of the canal may be not complete, and a positive pressure is generated on the cupula, which generates a constant stimulation of the affected side cupula. As in the previous clinical situation, repeated head shaking maneuver may also clinically transform the irritative fixed- nystagmus into a geotropic DCPN. In this regard, incomplete HSC jamming in association with vertical cupulolithiasis of the posterior semicircular canal on the opposite side has also been reported. In this particular clinical situation, a torsional component of the nystagmus may be observed at the same time on examination [9]. Therefore, both pathophysiologic disorders presented above can be considered another atypical form of HSC-BPPV eye movement presentation not previously described in ICVD [6, 7, 9] (Table 1).