Horizontal canal BPPV: understanding the mechanisms

Описание: Presentation during Vertigo Academy International Global Summit- 2 at 18th April, 2021. I explained the mechanisms of horizontal canal short arm canalithiasis, heavy cupula, light cupula and canalith jam.
1. Horizontal semicircular canal BPPV accounts for 22% of all BPPV cases,
2. In “short-arm” or anterior segment or canalithiasis,
3. The otoliths are in the periampullary area.
a) They may be near, but not attached to the canalicular side of the cupula,
b) or may be near to the utricular side.
5. When the involved ear is lowermost: apogeotropic horizontal nystagmus occurs due to these 3 possible movement of the otoliths.
6. Apogeotrophic nystagmus during right roll test.
7. When the sick ear is uppermost; there are two possibilities depending on the periampullatory position of the otoliths:
a) If the otoconia fall onto the cupula: an excitatory cupular deflection occurs,
8. And this leads to an apogeotropic nystagmus; which is stronger than the previous one.
9. b)- in the second possibility; otoliths located between the cupula and utricle fall into the utricle, also creating an excitatory stimulus.
10. The resulting apogeotrophic nystagmus is also stronger than lying on the sick side.
11. Remember that temporary geotropic direction-changing horizontal positional nystagmus is observed in canalolithiasis.
However, persistent nystagmus is the hallmark of cupulopathy: cupulolithiasis or light cupula
12. If the cupula is heavier than the surrounding endolymph, it is pulled downward, resulting in persistent apogeotropic DCPN.
13. Right Heavy cupula, canalicular side, Supine position.
14. During right roll: Apogeotrophic nystagmus occurs
15. During left roll: Apogeotrophic nystagmus occurs: note that it is stronger on the healthy side
16. Rarely, particles may be attached to the utricular side of the cupula.
17. Right Heavy cupula, utricular side, Supine position.
18. Right Heavy cupula, utricular side, right roll: Apogeotrophic nystagmus.
19. Right Heavy cupula, utricular side, left roll: Apogeotrophic: stronger on the healthy side. WE CAN NOT DIFFERENTIATE THOSE TWO TYPES OF HEAVY CUPULA.
20. Lets talk about Light (buoyant) cupula
21. Buoyant means to be able to keep afloat, or rise to the top of a liquid
22. Right horizontal canal light cupula: The cupula is lighter than the surrounding endolymph, in the supine position, a persistent left-beating nystagmus may be observed due to an inhibitory deflection of the cupula by buoyancy.
23. During RIGHT roll: Geotrophic nystagmus occurs, with little or no latency and lasts for at least 2 minutes.
24. During LEFT roll: ampulofugal deflection of the right cupula induces stronger geotropic nystagmus, due to the Ewalds second law.
25. Etiology is thought to be due to changes in the density of the cupula or endolymph.
Disruption of blood brain barrier may lead to increased proteins in the inner ear (ie. meningitis) and may also be a cause.
26. The pathogenesis remains unclear and so far, five hypotheses have been put forward.
27. Diagnosis is suspected when:
Roll Test: Persistent horizontal nystagmus; Geotrophic, No latency, Stronger towards the normal ear; Bow: beats to the affected side, Lean: beats to the healthy side; Null point: when the head is rotated 15- 450 to the affected side
NO OTHER CAUSES (Central/Unilateral periperal hypofunction)
28. Large masses of otoconia could be trapped inside the canals, like it happened in the suez canal. These plugs may be more common than appreciated and might be responsible for unusual patterns of nystagmus.
29. As the debris moves to a narrower portion of the hSCC, otoconia may occlude the lumen and become “jammed”; this may happen spontaneously or as a complication following a repositioning maneuver.
30. Canal jam induces a prolonged utriculofugal or utriculopetal deviation of the cupula and both would cause a nonfatiguing nystagmus regardless of the head position.
31. Horizontal head shaking may lead to a canal jam.
32. Rapid head shaking in the opposite direction moves the otolithic mass, plugging the canal. This cuts off the endolymph flow and prevents the deflected cupula to return back to its resting position leading to a persistent nystagmus (jam).
33. Example of otolith debris blocking the lumen within the right H SCC and deflecting the cupula in inhibition.
34. The largest cupular deflection occurs during head position rolled toward the unaffected (left) side, which progressively reduces, but though does not stop, as the subject moves to the supine or,
to lying on their affected right side
37. Canal jam is diagnosed when there is:
1. Direction fixed spontaneous horizontal nystagmus
2. that does not change direction with positional tests
3. Velocity of the positional nystagmus and intensity of vertigo depends on head position
4. Conversion of unidirectional positional nystagmus to geotropic nystagmus. Reversal of nystagmus (conversion: geotropization) is critical to be confident in diagnosing canalith jam.