A brief word of caution – this week’s blog is not for general consumption. It will be confusing to those not very familiar with Benign Paroxysmal Positional Vertigo (BPPV).
Last week, I blogged about some recent courses I had taught, and promised to post about a new trick I learned in the process.
I was about halfway through a 90-minute talk on BPPV, and the subject had steered toward horizontal canal (also known as Lateral Canal) BPPV. I had just finished describing the two most common nystagmus patterns associated with this condition. In the Canalithiasis version (where the particles are free floating in the horizontal canal), you will typically see right-beating nystagmus when you roll the patient’s head to the right supine position. The nystagmus will change directions to a left-beat nystagmus when you roll their head to the left supine position.
In the cupulolithiasis version (where the particles are attached or “stuck” to the cupula), you will see just the opposite. You will observe left-beat nystagmus in head right supine, and right-beat nystagmus in head left supine. There is a well-accepted treatment for the canalithiasis version known as the “log roll” or “barbecue roll” maneuver where the patient completes a full 360-degree roll away from the affected side.
So, how do you know which side is affected? Traditionally, it has been believed that the particles were on the side with the most intense nystagmus, but to some degree that could be affected by the order of your tests. Due to the fatiguing response from head movement, you could get a lesser response from the affected ear if you test it second. I was trying to make that point when someone asked about the “Bow and Lean” test. Of course, my response was “The what?” “The butterbean test?” (Have I mentioned I have some hearing loss?)
At this point, I felt the smart thing to do was surrender the podium to my co-presenter, Dr. Joel Goebel, who graciously explained how this test helps identify which ear is the culprit in horizontal canal BPPV. The point of the test is to stimulate both horizontal canals simultaneously by “bowing,” or leaning forward into a nose down position. In this situation, if there are free floating particles in one of the horizontal canals, they will flow TOWARD the cupula on the affected side. This results in an excitatory response in the affected canal and causes the eye to be pushed away (slow phase) from the affected side. Just like a warm caloric, the fast phase of the nystagmus would also beat toward the affected side.
This is a simple, but brilliant concept that had eluded me (as had the related literature) up until now.
