The following article wants to get a reasoned interpretation of the various maneuvers that will be described in the most elementary way possible, trying to understand, step by step, what happens inside the semicircular canals in performing the maneuvers themselves.
We have already diagnosed a benign positional paroxysmal vertigo of the lateral canal. Liberating maneuvers have the purpose to lead and facilitate the sliding of the mobile otoconial mass, inside the lateral canal, towards the utricle.
The maneuvers proposed are all valid, and the choice to perform one rather than the other is often taken by the clinician for different and contingent factors: the diagnostic manoeuvre adopted, the position reached by the patient at the moment of diagnosis, the experience of the clinician and his preferences as well.
Let us briefly remind the pathophysiology of the lateral canal BPPV.
- The otoconia detached from the utricular macula slide inside the lateral semicircular canal (LSC). When the patient reaches particular positions (decubitus) or performs particular head movements, he induces the slide of the otoconial mass. This creates an endolymphatic current that can be ampullifugal (that means the endolymphatic current moves away from the ampulla) or ampullipetal (if it moves toward the ampulla), depending on the position of the otoconial mass inside the canal.In the Lateral Semicircular Canal (LCS) the ampullipetal endolymphatic current is excitatory, while the ampullifugal current is inhibitory.
The Lateral Semicircular Canal (LCS) is functionally connected to the nucleus of the III and VI cranial nerve and, through them, with the extrinsic eyes muscles. The stimulation of an LCS lead:
- The contraction of the ipsilateral rectus medialis muscle and contralateral rectus lateralis muscle.
- The relaxation of the ipsilateral rectus lateralis muscle and contralateral rectus medialis muscle.
The clinical examination shows a nistagmus which is horizontal pure, which means without torsional or vertical components, as it’s been generated exclusively by the ampullar receptor of the LSC. It is paroxysmal, geotropic, or apogeotropic, slightly inhibited by fixation, fatiguing, and exhaustible.
In the Geotropic form, otoconial mass is placed in the non-ampullary arm of the LSC and therefore near the access to the utricle.
In the Apogeotropic variety the otoconial mass is placed in the ampullary arm of the LSC and therefore far from the canal access to the utricle (Short arm of the semicircular duct), so it is necessary, before performing the liberatory maneuver properly said, to perform a preliminary maneuver, called repositioning maneuver, that moves the otoconial mass into long canal’s arm.
The successful transformation from the apogeotropic form into a geotropic form can be easily documented by observing the direction of the nistagmus induced by the Pagnini-MClure maneuver.
The maneuver is simple to perform and very effective. The correct diagnosis leads us to the correct choice of which maneuver we must perform and finally to symptoms resolve.
The required instrumentation is straightforward but necessary: a visual fixation suppression system to be able to read with extreme precision the characteristics of the observed nystagmus.
The manoeuvre is differently performed depending on which form we are treating: geotropic or apogeotropic form.
BPPV GEOTROPIC FORM – OTOCONIAL DEBRIS IN THE LONG ARM OF THE SEMICIRCULAR DUCT
Once identified the involved side, we proceed with the liberatory manoeuvre. In the following pictures, it is illustrated a hypothetical canalolithiasis of the non-ampullary arm of the left LSC.
The patient, sitting with his legs hanging out the bed, is quickly tilted on the healthy side until arrives with his head on our hand closed in fist where the patient lay his head
This positioning manoeuvre generates geotropic nystagmus which tends after a few minutes to disappear completely, sometimes it can persist for longer, but anyway, a progressive reduction of the angular slow-phase velocity (ASPV) will be observed.
The patient’s head is then rotated abruptly about 45 ° down towards the table:
The rotation can generate:
nystagmus having the same direction as the nystagmus previously observed, that disappears during the maintenance of the position itself;
the increase of angular slow-phase velocity (ASPV) of the previously shown nystagmus that had not been completely exhausted during the first positioning.
In both cases, the observed nystagmus is proof of the gliding of the otoconial mass towards the utricle.
But if during the second step, we don’t observe any nystagmus, it means that we have not induced any movement of the otoconial debris and therefore this indicates that the manoeuvre we are performing has not been effective.
The patient is returned to a sitting position with a quick movement.
The manoeuvre is repeated three times, and if it is effective, at each time the nystagmus progressively reduces until it disappears.
BPPV IN THE APOGEOTROPIC FORM: OTOCONIAL MASS IN THE AMPULLARY (SHORT) ARM.
We start from the same position as we described before.
The patient, sitting with his legs hanging out the bed, is quickly tilted on the involved side until arrives with his head on our hand closed in fist where he lay his head
This positioning manoeuvre generates apogeotropic nystagmus, which means it beats upwards, which tends after a little time to disappear completely, sometimes it can persist for longer but anyway a progressive reduction of the angular slow-phase velocity (ASPV) will be observed.
If the transformation manoeuvre is effective, we observe, the reappearance of the nystagmus (Apogeotropic) previously described or the increase of the angular slow-phase velocity (AVSP) if the previous nystagmus wasn’t completely exhausted.
The observation of the nystagmus described in the second step indicates the sliding of the otoconial debris towards the non-ampullary arm.
The patient is returned now to a sitting position with a quick movement.
The manoeuvre is repeated three times, and if it is effective, at each time the intensity of the nystagmus reduces progressively until it disappears.
Then it is performed the Pagnini-McClure manoeuvre to confirm the transformation from the apogeotropic into the geotropic form.
Now it is possible to perform the liberating manoeuvre above described.
The unsuccessful transformation from the apogeotropic into the geotropic form is due to otoconial debris adhered to the ampullary cupula, or there is a narrow tract in the semicircular canal that hampers the slipping of the otoconial debris.
When the otoconial mass finds an obstacle stops its sliding towards the utricle and comes back.
In this case, we recommend not insisting on performing other maneuvers, because they only generate vertigo without any resolution of the PPVB that we want to treat.
Better to advise patients to perform “forced decubitus” as Professor Vannucchi described.