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The Bow and Lean Test

Dr. Danielle Gross, PT, DPT

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.

Cupulolithiasis:

  • immediate onset of vertigo when the patient is moved into a provoking position 
  • persistent (non stop, lasting well over 1 minute) vertigo/nystagmus as long as the patient remains in the provoking position
Canalithiasis:
  • may have a delay of onset, or latency, of vertigo/nystagmus lasting anywhere between 1 and 40 seconds when placed in a provoking position
  • there is a fluctuation in intensity of vertigo and nystagmus, first increasing in severity and then slowly decreasing in severity until it disappears in less than 60 seconds of maintaining the provoking position
So in short: Cupulolithiasis causes nystagmus and symptoms lasting greater than one minute. Canalithiasis should present with a burst of nystagmus and symptoms that dissipate in under 1 minute.

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.

Bow

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.

  • Instruct the patient to drop their head into flexion (approximately 30 degrees), and lean forward another 90 degrees. 30 degrees is required to move the canal parallel to floor, and then additional 90 degrees is required to position the cupula perpendicular to gravity
  • The patient shoulder stay in this position for 1-2 minutes.
  • Observe for nystagmus and the direction, as well as ask for associated complaints of dizziness
Source: Susan J. Herdman, Richard A. Clendaniel: Vestibular Rehabilitation, 4th Edition, www.FADavisPTCollection.com, Copyright © F. A. Davis Company All rights reserved

Bow Test: Canalithiasis

  • Otoconia is free floating in the canal
  • When the patient bows forward, otoconia displaced in the posterior portion of the horizontal will move toward the cupula, deflecting the cupula toward the utricle, creating an Excitatory Response. (making the involved ear more neurally active)
  • Nystagmus should beat TOWARDS affected side
  • Example: Right Ear Horizontal Canal BPPV= Right-beating Nystagmus with bow position (SAME SIDE)
  • Nystagmus will not be persistent 

Bow Test: Cupulolithiasis

  • Otoconia is adhered to the cupula
  • When the patient bows forward, the cupula, which is heavy from the adhered otoconia, is pulled away from the utricle creating an Inhibitory Response, making the unaffected sided technically more neurally active in comparison to the affected side.
  • Nystagmus should beat AWAY from the affected side (with otoconia).
  • Nystagmus will be persistent

Lean

  • With the patient in sitting with goggles on and fixation removed, instruct the patient to lean the head backwards 60 degrees. 60 degrees of extension is required since the horizontal canals sit at an approximate 30-degree angle in the head. An additional 60 degrees of elevation is required to place the cupula perpendicular, and most sensitive to gravity.
  • Hold the position for 1-2 minutes
  • Observe the directions of the nystagmus, as well as ask for associated complaints of dizziness

Lean Test: Canalithiasis

  • Free floating otoconia may now be located in the anterior portion of the horizontal canal following the bow test
  • When the patient leans back, the otoconia moves away from the cupula, which will deflect the cupula away from the utricle creating an Inhibitory Response.
  • Nystagmus should beat AWAY FROM the affected.
  • Nystagmus will not be persistent

Lean Test: Cupulolithiasis

  • Otoconia is adhered to the cupula
  • When the patient leans back, the debris sits on top of the cupula, weighing the cupula down towards the utricle, creating an Excitatory Response
  • Nystagmus should beat TOWARDS the affected side

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

  • Video: Dr. Danielle Gross PT, DPT FYZICAL Therapy & Balance Center of Rockville, MD
  • Bow and Lean Illustrations source:  Susan J. Herdman, Richard A. Clendaniel: Vestibular Rehabilitation, 4th Edition, www.FADavisPTCollection.com, Copyright © F. A. Davis Company All rights reserved
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