Positional nystagmus from the lateral canal is reliably elicited by the “Pagnini-McClure test,” also called the “supine head roll test,” a maneuver that acts in a plane parallel to that of the lateral canal [13, 14]. The patient is first brought from the sitting to the supine position, with the head straight (nose upward) and bent about 30° forward, looking for the appearance of any positional nystagmus. Then the patient’s head is rolled 90° to one side. After that, the head is rotated 180° to the other side, looking for changes in the direction and intensity of nystagmus. According to the different locations of otoconial debris in the canal, LC-BPPV can be divided into two variants, the more common one with geotropic nystagmus and the less common one with apogeotropic nystagmus.

Once otoconial debris have entered the lateral canal, they move under the force of gravity, tending to settle at the bottom of the canal, far from the cupula. When the patient is moved from the sitting to the supine position with the head straight, the debris gravitate downward to the lower portion of the canal, away from the ampulla. This causes an inhibitory ampullofugal endolymphatic flow and a mild horizontal nystagmus toward the unaffected ear [15] (Fig. 12.2). The subsequent rotation of the head toward the affected ear causes the particles to fall toward the ampulla, producing an excitatory flow and an intense horizontal nystagmus beating toward the lower ear. It is named geotropic because it beats toward the ground. When the head is then rolled to the other side (to the unaffected ear), the particles fall in the opposite direction and cause an inhibitory ampullofugal stimulus. This provokes an inversion of nystagmus direction, i.e., beating toward the opposite, healthy ear (again geotropic) (Fig. 12.3).

Geotropic positional nystagmus, when paroxysmal, is always due to canalolithiasis and does not require differential diagnosis. There are reports of horizontal positional nystagmus, geotropic, stationary, and long lasting, attributed to light cupula [16].

The apogeotropic variant is due to a different position of particles inside the lateral canal. According to cupulolithiasis theory, they can be attached to the cupula, on the canal side, on the utricular side, or both, and when the head is turned on its side, the heavy cupulae are deflected by gravity. When the head is rotated so that the affected side is down, the deflection will be toward the ground, and the resulting nystagmus will result from an inhibitory stimulus, that is, toward the opposite, normal, side (apogeotropic). In contrast, when the head is rotated so that the affected ear is up, the heavy cupulae will deflect toward the utriculus and the resulting “excitatory” nystagmus will be directed toward the uppermost affected ear (again apogeotropic). The intensity of nystagmus again reflects the difference in the stimulation (excitatory/inhibitory) of vestibular end organs, with the strongest nystagmus beating toward the affected ear.

There is also the possibility that the apogeotropic variant is due to canalolithiasis. If debris are located near the ampulla of the lateral canal, on its anterior part, they can move in the opposite direction with respect to the geotropic variant (Fig. 12.4).

Cupulolithiasis should be characterized by less violent and more persistent positional nystagmus. Canalolithiasis is more likely when positional nystagmus is very intense and when the apogeotropic variant is easily transformed into the geotropic one, by diagnostic or therapeutic maneuvers. The characteristics of positional nystagmus due to LC-BPPV are shown in Table 12.2.

The diagnostic key for LC-BPPV is the finding of a horizontal and direction changing positional nystagmus evoked by the supine head roll test. Its latency is usually shorter than that of the PC-BPPV; it is generally more intense and lasts longer, usually less than a minute. It is sometimes necessary to repeat the diagnostic maneuvers, because the first rotation may not have evoked the positional nystagmus. Repetition of the rotation is also helpful to identify the more intense nystagmus and the pathological ear. Patients with LC-BPPV may also exhibit a mild “spontaneous” horizontal nystagmus while in the sitting position [13]. This pseudo-spontaneous nystagmus is strongly modulated by head position and movement [17, 18].

Unlike the geotropic variant, the apogeotropic variant requires a differential diagnosis with dysfunction of the central vestibular system, especially if positional nystagmus is not paroxysmal. The best way to obtain a correct diagnosis is probably by exclusion. Posterior fossa lesions quite often produce symptoms that are difficult to ignore and lead to additional ocular motor abnormalities such as gaze-evoked nystagmus, impaired smooth pursuit or saccades, and other neurological abnormalities. A clinical history of previous episodes of PC-BPPV is often a clue. In cases of doubt, especially if apogeotropic nystagmus does not disappear in a few days or does not change its direction, an MRI of the brain is necessary.

Anterior canal (AC) BPPV is much rarer than LC- and PC-BPPV because of the superior anatomical position of the canal. It is improbable for debris to enter this canal, and self-clearing is facilitated because the posterior arm of this canal descends directly into the common crus. AC-BPPV can be detected with both Dix-Hallpike maneuvers since the anterior canals are coplanar to the PCs of the opposite side. In fact, the best way to elicit a positional nystagmus due to the ACs is with straight head hanging, by bringing the patient to the supine position with the head 30° (or even more) below the earth horizontal [19, 20]. When the Dix-Hallpike maneuver provokes a mixed vertical-torsional nystagmus and the fast phase of the vertical component is downbeating, anterior canal involvement may be responsible. The torsional component beats with the top pole of the eye toward the upper ear. This is because the Dix-Hallpike maneuver on one side acts on the plane of the AC of the contralateral side. Otoconial debris will fall away from the ampulla, provoking an excitatory stimulus to the ipsilateral superior rectus and to the contralateral inferior oblique muscles, that is, the antagonists of the muscles connected to the PC.

In fact, canalolithiasis of the AC is still debated because patients with positional downbeating nystagmus (pDBN) show some features that are difficult to justify. Nystagmus can be vertical-torsional but is often purely vertical, relatively sustained, and of low intensity. Very often, the nystagmus does not reverse its direction when the patient is returned to the sitting position, in spite of the contemporary presence of important vertigo or unsteadiness. Some of these features may be justified [19], some not. Moreover, patients with pDBN are more common than previously reported [11], probably with the same frequency of presentation as LC-BPPV in the geotropic form, in contrast to the anatomy of the labyrinth. Many of them were previously affected or will develop a typical PC-BPPV. The course of the syndrome, often characterized by a rapid and spontaneous remission, is benign, but its relationship to canalolithiasis of the AC needs to be confirmed. Other pathomechanisms must also be considered. Theoretically, pDBN can also be observed in atypical forms of PC-BPPV, when the debris are located in the non-ampullar arm of a PC and move in a direction opposite to the expected one, similar to the pathomechanism of apogeotropic nystagmus in the lateral canal [21]. Furthermore, debris could also be located in the short arm of a PC [22], causing deflection of the cupula due to debris falling into the utriculus.

On the other hand, it must be emphasized that a pDBN can be due to damage to the vestibular cerebellum even though this is improbable when positional nystagmus is the only sign and/or there is a rapid resolution.

The therapy of choice for BPPV is physical treatment. Physical therapy aims to eliminate the episodes of positional vertigo by forcing the otoconial debris to come out of the semicircular canals. Special movements and positions of the head and body are used to trigger a series of clinical events which are consistent with the canalolithiasis hypothesis. Therapies for PC- and LC-BPPV have been validated. On the other hand, specific diagnostic criteria and effective treatment for the anterior canal variant of BPPV are still illusive. Surgery and medications play a minor role in BPPV. Below, we summarize the main therapeutic maneuvers for BPPV, details of which can be found in the references.