Rarely, maneuvers don’t seem to work, even though the vertigo seems to be BPPV. The affected person is able to make spells happen by making head movements like lying down, rolling over or tipping the head up, but the particles seem to be stuck, unable to exit the ear. Each time a maneuver is done, the vertigo remains the same, rather than improving.
For the last 50 years, this has been blamed on particles attached to the cupula, the main spinning sensor in the semicircular canals. The particles in BPPV move freely in the canals and can be moved out by rotating the head, but in this condition they won’t exit. We don’t believe this is caused by otoconia stuck on the cupula. Instead, we believe they form a blockage in a narrow part of the canal.
This problem is called canalith jam. Otoconia are very sticky, and they are very good at sticking to each other. This means that particles can enter the semicircular canals one at a time, but once inside can stick together until they form a large, irregular clump. These clumps can include pieces of the membrane that attaches them to the gravity sensor, forming a cluster rather like crumpled pieces of paper.
The problem with this is that the semicircular canal is a tube with a large swelling on the end containing the sensor, called the ampulla. Individual particles can easily enter this enlarged area, but have to pass through a gradually tapering funnel in order to get back into the semicircular canal. If they form a larger clump in the ampulla, this is a problem. Imagine pouring sugar through a kitchen funnel—it’s simple. It’s harder to pour brown sugar, which sticks together and forms clumps. Now try to drop pieces of crumpled paper through—that’s very difficult. Rough, irregular clumps don’t pass easily through narrow places.
The symptom this causes is just like BPPV, but maneuvers don’t seem to work. The particles are usually hanging up very close to the sensor, moving back and forth between the cupula and the chokepoint in the canal. Since they are blocked from exiting, maneuvers have a hard time resolving the problem. We’ll discuss how this is treated in the next post.