A Closer Look at Horizontal Semicircular Canal Jams

I had written a blog entry back in 2017 about a case study of mine that I had felt was similar to a Horizontal Semicircular Canal Jam: “Stuck BPPV: A Canalith Jam Case Study”. Recently, a new article by Michael Schubert, Janet Helminski, David Zee and a few other researchers was published detailing two specific case studies of horizontal semicircular canal jams. They provide a clear picture of what should be considered diagnostic criteria for this phenomenon. They also touch on a theory about the “light cupula” phenomenon. Overall, it’s a fantastic article/case study and you should read it!

First let’s talk about the prevalence of Horizontal Canal BPPV. “Horizontal semicircular canal (hSCC) benign paroxysmal positional vertigo (BPPV) accounts for 22% of all BPPV, with paroxysmal nystagmus during positional testing being geotropic in 70%, apogeotropic in 28%, and direction-fixed in 1.8%”² So overall, the chances of seeing direction fixed nystagmus during positional testing, where the velocity of the nystagmus seems dependent on the patient’s head position, is very small. However, it’s important to have an idea of what you’re looking at if you happen to evaluate a patient with this presentation! This type of patient could easily be mistaken for having a central issue rather than BPPV.

A canal jam occurs when there is a partial or complete obstruction within the lumen of the canal. The study suggests that this can occur when debris is moving from a larger section of the canal and gets bottle-necked into a more narrow portion of the canal. This can either happen spontaneously, or even during canalith repositioning maneuvers.

When an obstruction occurs, it is thought that the jam may create a prolonged inhibitory or excitatory stimulus due to the prolonged deflection of the cupula. This would cause persistent direction fixed horizontal nystagmus regardless of head position.

What happens when the jam breaks up? The answer is geotropization. This is the liberation of the jam which causes an immediate change of the nystagmus from direction-fixed to geotropic nystagmus. Once converted to geotropic nystagmus, the BPPV can be treated using the barbecue roll (log roll) or Gufoni's liberatory maneuver.²

Case 1: Overview

• 56 y/o female
• 4 days since initial onset, reports she cannot lie on left side due to severe vertigo
• No significant medical history
• OM exam:
  • Spontaneous left beating nystagmus (w/ fixation and fixation removed)
  • Smooth Pursuit and Saccades: WNL
  • Head impulse testing not performed
• Positional Testing
  • Dix-Hallpike (DH): persistent L beat nystagmus noted bilaterally, more intense in L DH
  • Supine Roll Test (SRT):L beat nystagmus with velocity similar to the nystagmus in upright position.
    • R SRT: left beat nystagmus initially reduced in intensity, however, after ~ 10 second mildly increased and then settled to a velocity of ~ 6 deg/sec persisting beyond 100 seconds.
    • L SRT: left beating nystagmus increased robustly to 24 deg/sec before settling to 13 deg/sec persisting beyond 120 seconds
  • The SRT was performed a second time, during which geotropization occurred.
    • Nystagmus was converted to geotropic, with velocity/intensity greater in a Right Roll (suggesting right side involvement)
  • A Gufoni maneuver was performed which resolved the BPPV.
  • After being symptoms free for 9 days, the patient returned and presented with Right Posterior Canal BPPV, canalithiasis-type which was treated successfully with a liberatory maneuver for the posterior canal.
  • 15 day follow up: Patient was symptom free

Conclusion: The patient presented with a Right Horizontal Semicircular Canal Jam in which the cupula was deflected to create a prolonged inhibitory response.

Case 2: Overview

• 63 y/o female
• Initial onset 3 days prior:
  • Reported increased dizziness with turning head back/forth
  • Intensity of dizziness would vary when lying down: dizziness experienced when lying on right side only, no dizziness when lying on left
  • Dizziness was most severe when lying supine
  • Patient would vomit if symptoms became too severe
• No significant medical history, no neurological findings upon exam
• OM exam in room light: normal
• Infrared Video Goggle testing:
  • Fixation removed:strong/fixed unidirectional horizontal right beating nystagmus was observed in all positions of gaze, intensified with right gaze
  • Positional Testing: DH, SRT, and bow/lean were all performed
    • Continued strong right beating nystagmus noted regardless of position.
    • DH: right beating nystagmus also included a torsional component
    • SRT: most symptomatic in neutral position, most relief with head turned 70 degrees to the left
  • The patient became too symptomatic during testing and refused further treatment. She returned home and slept on her left side with her head slightly elevated.
    • About 4 hours later, the patient called the therapist to report a resolution in symptoms.
  • The patient returned 3 days later, reporting feeling 90% better.
    • On examination, she still had direction-fixed, right beat nystagmus with fixation removed.
    • In supine, her nystagmus changed to left beating
      • This suggestsutriculofugal (inhibition) movement of the otoconia and endolymph within the right hSCC.
    • SRT: positional nystagmus was low amplitude, geotropic, lasting 1 minute.
    • The patient was treated with three cycles of the BBQ roll maneuver for the right hSCC
  • The patient followed up by phone to report complete resolution of symptoms.

Conclusion:The patient presented with a Right Horizontal Semicircular Canal Jam in which the cupula was deflected to create a prolonged excitatory response.

This article provides great criteria to use for identifying whether your patient has a canal jam:

1. Direction fixed spontaneous nystagmus with fixation removed.
2. Direction fixed spontaneous nystagmus during positional testing.
3. The velocity of the positional nystagmus and intensity of vertigo depend on supine roll head position.
4. Conversion of unidirectional positional nystagmus to geotropic nystagmus.

Determining the side of involvement could be difficult without the conversion of the unidirectional positional nystagmus to geotropic nystagmus. Take both cases in this article for example. Both patients had a Right Horizontal Semicircular Canal Jam, but each presented differently due to the direction of prolonged cupula deflection. Once the jam is cleared, and the patient presents with a more typical presentation of canalithiasis or cupulolithiasis, the side of involvement can be identified.

Based on the presentation of these two cases, there remain few differential diagnoses that would cause the sudden reversal of nystagmus during positional testing, and thus this finding is critical to be confident in diagnosing canalith jam. Vestibular migraine can cause a persistent nystagmus that is position dependent, though the velocities of the nystagmus tend to be less than reported in the case studies.²

In one last final note, the authors suggest that “Semicircular canal membrane plugs (jams), even perhaps more than one in a single canal, may be more common than appreciated and might be responsible for other unusual patterns of nystagmus such as persistent geotropic nystagmus with vertigo that currently is attributed to the “light cupula” phenomenon.”²

After reading through this study, it’s safe to say that my patient in 2017 was not experiencing a true canal jam, but more likely experiencing a form of Horizontal Canal BPPV, Canalithiasis-type where the bolus of debris was moving freely within the canal but was too large to pass through the canal opening back into the utricle.

1. Epley JM. Positional vertigo related to semicircular canalithiasis. Otolaryngol Head Neck Surg. 1995;112(1):154-161. https://doi.org/ 10.1016/S0194-59989570315-2.
2. Schubert MC, Helminski J, Zee DS, et al. Horizontal semicircular canal jam: Two new cases and possible mechanisms. Laryngoscope Investigative Otolaryngology. 2020;5:163–167. https://doi.org/10.1002/ lio2.352

Link to article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7042637/pdf/LIO2-5-163.pdf