Horizontal Canal BPPV can be tricky to diagnose. You will first have to determine whether the patient presents with cupulolithasis or canalithiasis, and then recognize which ear is the affected ear. Sometimes the testing is obvious, and sometimes it is not! When the Roll Test or the patient does not help yield an obvious result, we have The Bow and Lean Test to help us out.
First, lets discuss the difference between Canalithiasis and Cupulolithiasis. Each term refers to where the otoconia (also commonly known as crystals) are displaced. Canalithiasis indicates that the otoconia are free floating and moving within the canal. Otoconia is significantly heavier than the endolymph it is sitting in. They sink like stones in water through the canal whenever the patient changes positions. As the otoconia moves through the canal, they pull the endolymph with them causing the cupula, the sensor at one end of the canal, to deflect in a certain direction. This creates an inappropriate excitation or inhibition in the canal that they are displaced in, which in turn causes nystagmus and associated complaints of vertigo for the patient. Cupulolithiasis indicates that the otoconia are adhered to the cupula. The cupula is a gel-like membrane that sits over the hair cells that detect the angular acceleration of head movement. Examples of angular head motion includes nodding your head yes, shaking your head no, or tilting your head side to side. During these motions, endolymph inside the canal moves and billows the cupula one way or another. The cupula has the same density as the endolymph that surrounds it so that only motion makes it billow, not gravity. However, in the case of cupulolithiasis, the otoconia weigh down the cupula making it heavy and sensitive to its relation to gravity.
The are distinct characteristics of cupulolithiasis and canalithiasis.
So how does the Bow and Lean Test work?
If you can recognize the difference between Canalithiasis and Cupulolithiasis, the Bow and Lean Test will give you indication which ear is the affected ear so that you can administer the appropriate treatment. Ewald's Second Law is important in this situation:
Fluid flow, or otoconia movement, TOWARDS the cupula in the HORIZONTAL canal is an excitatory stimulus.
This means when the cupula deflects toward the utricle/away from the canal, an excitation response occurs. When the cupula deflects away from the utricle/towards the canal, an inhibition response occurs. Nystagmus always beats toward the more neurally active ear. When excited, the ear is considered more neurally active.
Below is a summarized chart of Cupulolithiasis and Canalithiasis with the Bow and Lean Test created by Brian Werner, PT, MPT, National Director of Balance Center Programs with FYZICAL Therapy & Balance Centers.
Start by having the patient sit on the edge of a treatment table. Frenzel Goggles or Infrared Videonystagmography Goggles are recommended to remove visual fixation. By removing the patient's ability to visually fixate on a target, horizontal nystagmus will not be suppressed by the brain and be easily visible to the clinician.
Bow Test: Canalithiasis
Bow Test: Cupulolithiasis
Lean Test: Canalithiasis
Lean Test: Cupulolithiasis
Nystagmus will be persistent
Bow and Lean Test Clinical Example
This examination clip demonstrates the Bow and Lean Test with a patient who presents with Right Horizontal Canal BPPV, Cupulolithiasis-Type
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