Alain SÉMONT

Introduction
Demanding differential diagnoses for a mechanical disorder whose physiology is acknowledged to be a delicate matter. This implies above all eliminating the methodological errors in the search for the signs that confirm the disorder, and then to make the pertinent connection between the signs observed and their significance.

Before this, there is the clinical session comprising a series of questions. With mechanical disorders, the responses should be stereotypical, shared by all patients, and replicable and the disorder itself should have a determined length of duration. However, sometimes certain minor supplementary details or missing details sew the seed of doubt that requires a more cautious and rigorous search for clues. Known as benign paroxysmal positional vertigo, sometimes it is not always benign. The consequences of a too vigorous therapeutic manoeuvre can have dramatic consequences.

Clinical Reminder
Vertigo: if we side with the strongly held belief that you can not have vertigo without a nystagmus, but that a nystagmus can occur in the absence of vertigos, we conclude that the subject has to follow a rotatory movement of their visual scene. It can be considered a somewhat simplistic idea, but often true, that rotatory vertigo is peripheral in nature, whereas the sensations: head spinning, heavy headedness or light headedness, unease, a sensation of fainting etc… can not be part of the symptoms of BPPV.

Positional: vertigo is induced once the subject is in a specific position. At the onset of the vertigo, the subject is not moving. It is not therefore a response to a vestibular stimulation through movement but rather a vestibular response to a movement of the endolymph without any movement of the head or body.

Paroxysmal: this means that the intensity of the vertigo is not linear. The subject feels the vertigo arrive before the observer sees the nystagmus. The sensation continues to intensify through to paroxysm, dissipates then slowly disappears.

Benign: the generally accepted cause of the migration of debris into the canal effectively makes it a benign disorder. Conversely, literature provides ample examples of "BPPV" that have been indicators of a serious disorder of the posterior fossa: infiltrating tumours on the brain stem, an abscess on the cerebellum etc…It appears difficult today, given the level of sophistication of the resources that practitioners have at their disposal, to think that such a case could slip through the net. However, humility compels us to say that an excess of confidence, a question and answer session that is too superficial, an incomplete search for clues, even if the probability of an unfortunate outcome is very low, demonstrate that just one time is all it takes!

To be pragmatic: a positional vertigo is a rotatory vertigo:

• that lasts between fifteen and twenty seconds,
• that can be triggered at will (this meaning that one can also avoid triggering it),
• that is triggered with the head in the same position, nothing else,
• that primarily happens in the evening when one lies down with the head turned to one side.
• We can continue by stating that:
• vertigo appears as a nystagmus,
• the nystagmus is paroxysmal,
• it fades away as long as the position does not change,
• it is reversed upon return to the upright position along the posterior canal.

From our experience, reversal of the nystagmus is the most significant characteristic when it comes to stating that it is a BPPV and carrying out a liberatory manoeuvre should be considered. In fact, the positional nystagmus and its reversal are the characteristics that enable us to understand that it is caused by a free-floating amalgam in the endolymph. The forward and back movement brought on by the two opposing positions enable us to understand that there is indeed movement of the amalgam-endolymph in one direction or another.

The question and answer should therefore aim to discover from the patient’s explanations the clinical parameters for the appearance of the vertigo. Movements, positions, length, reproduction, context etc…

Errors in methodology
Once convinced that the description of the symptom does indeed correspond to our concept of BPPV, we move on to the provocation manoeuvres such as those described in the earlier sections.

One must however find out about the possible existence of another vestibular disorder prior to the appearance of the BPPV. Indeed, one must look for the existence of a nystagmus or not. This is usually done using a videoscopy in the dark. If, during the question and answer session, we discover a vestibular disorder, a spontaneous nystagmus should correspond to a known vestibular anomaly, whether it is peripheral or central. Absence of correspondence between the spontaneous nystagmus observed and the earlier supposed vestibular anomaly compels us to question the use of any BPPV therapeutic movements. A comprehensive otoneurological assessment should therefore be considered. A vertical spontaneous nystagmus with a history of supposed neuritis does not necessarily appear very logical.

In the absence of spontaneous nystagmus and/or central signs (gaze, saccadic pursuit), one can proceed with provocation manoeuvres. These are made using videoscopy goggles, but removing the eye patch and camera.

There are many reasons for this:

• We know that ocular fixation inhibits a peripheral nystagmus but that a torsional nystagmus is produced somewhere around the Z-axis, the axis of rotation of the eye ball, so it would be convenient if there were no inhibition of a torsional nystagmus.
• Conversely, one is able, thanks to this characteristic (of inhibition), break away from the horizontal and vertical components that might hamper the observation of a torsional nystagmus.
• In the case of a horizontal canal, the provoked nystagmus is so violent that even if it were possible to decrease its amplitude, it would never be able to be completely inhibited.
• The use of videoscopy goggles while keeping the eye patch in place and not filming it, in total darkness therefore, might result in false positives. In fact, the provocation movement, such as a manoeuvre of DIX and HALLPIKE, is enough to charge the velocity storage mechanism (VSM). Once the manoeuvre is carried out, the VSM will discharge producing saccadic eye movement that might be a mixture of torsional and vertical saccadic eye movement since the manoeuvre stimulates the vertical canals. Said observation of a nystagmus whose source is physiological in nature might make one think of a potential BPPV when in fact there is not one!! Therapeutic manoeuvres that follow on from this will not be effective, and for good reason, but might, by their untimely repetition, be at the source of cupula pathologies.

With the description of the manoeuvres, we have stressed the importance of being rigorous with the positions of the head so as to favour the drainage of the debris. During provocation manoeuvres, it is also important to check the angle of the head and more importantly the angle of the canal to favour the migration of the amalgam.

It is also worth remembering that the amalgam is glue-like and given that fact, latency time might be long. Especially if the patient, having been warned of the sensitive position of the head, manages to avoid provoking their vertigos. The amalgam risks getting stuck to the wall of the canal and not being freed from that position. It is important to know how to wait for the nystagmus to manifest itself. If it does not happen, and if the subject, while returning to the upright position, suffers a vertigo, it should be remembered that the observed nystagmus beats to the opposite side of the damaged ear. Similarly, if the DIX and HALLPIKE manoeuvre is practiced on the opposite side of the observed nystagmus, it might provide erroneous information about the damaged ear.

One must know how to persevere with the provocation manoeuvres when the observer sees nothing and the subject states that they provoked their vertigo the evening before, when getting into bed. The provocation manoeuvres should be carried out quicker, and more vigorously, but without being rough.

In short, it should never be forgotten that a nystagmus must be observed with the eye in the medial gaze position. The external eye muscles might, in the case of an eccentric eye, be able to completely invert the direction of the nystagmus.

Differential diagnosis
Any nystagmus observed under conditions of darkness on a subject in a lying-down position is not necessarily a BPPV. When errors in methodology are avoided, when the search for a spontaneous nystagmus does not come up with a result, when the particular characteristics of a BPPV are respected, the conditions have been met to enable one to carry out the therapeutic manoeuvre and see it then endorsed with a positive result.

It might be that a subject’s complaints and their insistence on finding relief as quickly as possible are such that the wish to do a good job by bypassing certain essential steps leads to a manoeuvre being carried out that can only lead to failure.

In short, they are subjects who present with complaints similar to those of BPPV, where position plays an important role, as does their discomfort and the unease that comes with it but which after rigorous observation are shown not to be BPPV.

Positional nystagmus is the sign which leads to quite a deal of confusion with healthcare professionals with limited experience in this field. Knowing that a positional nystagmus is a latent spontaneous nystagmus revealed by its position, there should not be any complaints. However, physiology teaches us that, influenced by the variety of degrees of sensitivity between individuals, when the speed of the slow phase passes 5°/s, the subject might see the visual scene move and subsequently describe it as a vertigo.

Under what conditions are we able to observe an increase in the speed of a slow phase?

• with a pressure syndrome in critical phase
• in a compliance anomaly of the round window. This could well be post-traumatic or after strenuous activity with the glottis sealed.

But the rigorous nature of the question and answer session should have enabled us to foresee these eventualities. It goes without saying that precaution should be taken during the observation of a positional nystagmus after kyphosis surgery. But it is better, despite everything, to mention it.

One should never underestimate the positional nystagmus described by certain authors as a cause of an expansive process of the cerebellopontine angle.

Earlier we shed some light on the consequences of the overuse of manoeuvres called pathology of the cupula. Indeed, it must be said that the cupulae are not built to stand the mechanical constraints we impose on them by repeating these manoeuvres, which some times, when they are carried out by healthcare professionals with little experience, can be brutal. We therefore observe, when the patient is positioned on their side, a geotropic torsional nystagmus, and not a paroxysmal one, which takes time to fade away. When the subject is then placed onto their other side, the same observation is made: namely a geotropic torsional nystagmus.

When the positional nystagmus is observed and reveals a vestibular disorder, the treatment provided is that of a vestibular disorder. When the nystagmus is the consequence of overzealousness, the subject must be immobilised and asked to avoid any movements and positions where signs and symptoms manifest themselves. These guidelines should be strictly followed for a period of 15 days. In most cases, subjects are then asymptomatic but depending on the intensity of the signs observed, advising them to follow the same guidelines for an additional fortnight might be both useful and necessary.

The central nystagmus. There is a wealth of literature about central lesions leading to nystagmus which can point to more serious underlying lesions that might have escaped unwary clinical staff. We won’t write out a long list but will simply remind ourselves of some common characteristics which are, in our opinion, sufficient for ordering an in-depth examination as soon as possible.

• projectile vomiting without nausea immediately after positioning of the subject,
• bias between the obvious suffering of the subject and the lack of obvious signs,
• pallor, sweating, a sense of impending death or the loss of consciousness when being put into the position without observing an acute nystagmus that would warrant such a reaction.  Basilar migraine is a prime example of this.
• One should never underestimate the incidence of Arnold-Chiari malformation when observing an inferior vertical nystagmus. Simply check for a fall in intensity by lifting up the subjects head with the neck in flexion.
• Vascularnervous conflicts do exist. As described by M. MOLLER, the high-frequency, short-lasting (5 seconds) nystagmus appears suddenly, and stops almost as quickly as it appears.

One might think that it is inappropriate to mistake such situations. Neurologists already know this as do the majority of ENT specialists. But BPPV has been subjected to a media craze whereby the term "the crystals" has replaced "Ménière" in the minds of many. My apologies to the reader.

Bibliography
In addition to the unrivalled work of Alain Sémont, scientific and medical details about differential diagnosis and the pathophysiologies of VCP are taken from the following publications:

Principles of Neurology by Raymond D. Adams and Maurice Victor
McGRAW-HILL Book Company A Blackston Publication
Vertebrobasilar Arterial Disease by Ramon Berguer and Louis R. Kaplan
Quality Medical Publishing, Inc St Louis

>> Please also consult the bibliography section of this site.