Conversion to Horizontal Canal BPPV

Since we discussed Horizontal Canal (HC) BPPV last week while discussing descriptive analogies we use in patient education, let’s talk a bit more about this variation of BPPV. A 2006 study states that HC BPPV accounts for as much as 13% of all cases of BPPV. My personal experience has been that it is more like 5%. That study looked at 169 patients, and I am considering probably over 15,000 patients. They did an exact count, and I am estimating.

Bottom line, if you see dizzy patients, you are going to encounter HC BPPV.

Maybe one reason for the difference is that I only count patients who walk in the door with HC BPPV, not those who are converted from Posterior Canal BPPV to HC BPPV during Canalith Repositioning (CRP). Sometimes when the otoconia debris exits the posterior canal (as planned), it enters the horizontal canal on the same side (duh). We see at least one of these a month. I refer to it as “easy in, easy out” because simply performing a quick CRP for that horizontal canal resolves the problem well over 90% of the time.

Why is it then that previously reported success rates for CRP of the horizontal canal are lower than for posterior canal BPPV, and far lower than the 90% range I experience in my office?

Well, I don’t know for sure, but I have a theory. Maybe all the “easy in, easy out” patients are unknowingly treating themselves simply by lying down and rolling over in bed. This is a movement that most people do naturally every night. Maybe only the more difficult cases make it as far as a vestibular specialist. That will certainly affect your success rate.

Why doesn’t this happen with the more common Posterior Canal BPPV? Primarily because the series of movements that effectively moves otoconia out of the posterior canal are not movements people make naturally.

Maybe this theory is completely wrong. Maybe it doesn’t even stand up to the scrutiny of “diagnostic plausibility” that I have discussed in the past. If you have some thoughts on this, please comment.

About Alan Desmond

Dr. Alan Desmond is the director of the Balance Disorders Program at Wake Forest Baptist Health Center, and holds an adjunct assistant professor faculty position at the Wake Forest School of Medicine. In 2015, he received the Presidents Award from the American Academy of Audiology.