Lateral semicircular canal benign paroxysmal positional vertigo diagnostic signs.

I read with interest the article entitled Converting apogeotropic into geotropic lateral canalolithiasis by headpitching manoeuvre in the sitting position by Califano et al. . The Authors describe their experience in transforming the apogeotropic LSC BPPV (Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo) into a geotropic one performing "a quick 60° forward flexion and a slow maximal backward-extension of the head" in the sitting position. Furthermore, many diagnostic tests and clinical signs concerning the diagnosis of the affected side in LSC BPPV are mentioned.

I would like to clarify some points regarding a few statements in the above-mentioned paper.

The Authors refer to the converting technique from apo to geo either as a "manoeuvre" or as a "test", but it would be more correct to call "test", the clinical procedure used to define clinical diagnostic signs and "manoeuvre", the therapeutic procedure. Besides, there is a clear difference between the Head Pitch Test already described to make the differential diagnosis between the Pseudo-Spontaneous Nystagmus and the Spontaneous Nystagmus, and the Head Pitch Manoeuvre described by the Authors as a procedure to reach the conversion of LSC BPPV from apo to geo. The former is performed by slowly bending the head 60° forward and then 30° backward, the latter is performed by a "a quick 60° forward flexion and a slow maximal backward-extension of the head". As far as concerns the diagnosis of the affected side, in LSC BPPV, a misleading list of clinical signs, improperly called "accessory signs of laterality" is given. In this regard, I should like to elucidate the following points:

The nystagmus observed in the upright position in LSC BPPV, known as Pseudo-Spontaneous Nystagmus (PSN), was first described in 2003 (Asprella-Libonati personal communication, cited by Nuti et al. ) and it was observed in a large series of patients in 2005 . This latter article pointed out the clinical value of this sign in diagnosing the affected side and identified a pathophysiological theory, attributing the PSN to the slow floating of the otoliths along the LSC bent 30° compared to the horizontal plane, so that it acts as an inclined plane on which the otoliths can gravitate following the same direction as the gravitational vector. The nystagmus (PSN) direction changes, induced by flexing and extending the patient’s head in the upright position, were described in 2006 .

A single pathophysiological theory explaining the PSN, its directional changes evoked by changing the head bending angle and its relation to other clinical diagnostic signs such as the nystagmus evoked by the Seated- Supine Test was described in 2008 . This same paper emphasizes the importance of the Head Pitch Test in the upright position in order to perform the differential diagnosis between the PSN and Spontaneous Nystagmus.

The main concept is a single theory: the nystagmus observed in LSC BPPV, in the upright position, with its modifications induced by slow flexing and extending the head (Head Pitch Test), and the nystagmus induced by the Seated Supine Positioning Test should be considered as the biological response to a single physical phenomena: the otoliths gravitate along the inclined plane of the Lateral Semicircular Canal. The only variable is the size of the gravity vector component which is parallel to the LSC plane, this is the only efficacious force vector in moving the otoliths along the LSC. Thus the acceleration, due to gravity on the debris, varies from zero (neutral point) when the LSC is orthogonal to the gravity axis (head flexed 30° forward in upright position), to the maximum when the LSC is parallel to the gravity vector (supine position, straight ahead head flexed 30°). The force of gravity (f) is: f = W g sin s (W = mass of the otoliths, g = Acceleration due to Gravity = 9.81 m/sec2, s = bending angle of the LSC plane with respect to the horizontal plane [Fig. 1]), so that s = 0° when the LSC plane is parallel to the horizontal plane and, in this case, the force of gravity has null effect f = W g sin s = W g sin 0 = 0; while s = 90° when the LSC plane is orthogonal to the horizontal plane and, in this case, the force of gravity has the maximum effect f = W g sin s = W g sin 90 = W g 1 = W g. If s is between 0° and 90°, f is between 0 and W g, so that the gravitational pull increases with the bending angle of the LSC.

Fig. 1.

The force of gravity (f) is: f = W g sin s (W = mass of the otoliths, g = Acceleration due to Gravity = 9.81 m/sec2, s = bending angle of the LSC plane with respect to the horizontal plane).

That being stated, I suggest to use the same terminology naming the LSC BPPV nystagmuses observed in the upright position and its modifications by performing the Head Pitch Test as "Pseudo-Spontaneous Nystagmus". In my opinion, definitions such as "bow and lean Ny", "head bending Ny" are misleading and should be removed.

Finally, I disagree with the Authors’ conclusions regarding the HPT: "Only in apogeotropic cases, should HPT be performed in the sitting position".

In my experience, I have been using the HPT in all the LSC BPPV for the last 5 years, at least. I never observed the conversion from geo to apo and vice-versa. Nevertheless, it is absolutely necessary to perform the HPT in order to correctly make the differential diagnosis between Spontaneous Nystagmus and Pseudo-Spontaneous Nystagmus and to diagnose the affected side early in LSC BPPB. The latter is the first principle in the aim to achieve the maximum patient compliance which is the purpose of my approaching strategy to LSC BPPV: "the Strategy of Minimum Stimulus" .