Superior Canal Dehiscence (SCD): Bedside Tests

Timothy C. Hain, MD   • Page last modified: July 6, 2020

See also: SCD (overview)SCD references

None of the bedside tests are very strong (i.e. both sensitive and specific). One mainly has to rely on lab tests (VEMP) followed by a proper CT scan. Still they are quick and if positive can point the clinician towards doing lab tests.

Tests that may be helpful in the office to identify SCD are as follows:

Somewhat sensitive is asking patients if they can "hear" a tuning fork (128 hZ) applied to their wrist. The latter method is of course vulnerable to suggestibility, but is quick and easy.

Pragmatically, one generally always tests for all of these at bedside, aside from fistula testing. The reason is that these bedside tests are quick, fairly specific when positive, and can increase one's enthusiasm to proceed with laboratory tests.

 

Valsalva test: (follow link for more detail)

In SCD, positive pressure or Valsalva against pinched nostrils produces downbeating nystagmus, with a torsional fast phase consistent with stimulation of the affected ear (CCW for right ear, CW for left ear). See example below. Negative pressure or Valsalva against a closed glottis may produce upbeating nystagmus and nystagmus beating with the torsional fast phase in the opposite direction (CW for right ear, CCW for left ear). We ourselves prefer the Valsalva against a closed glottis.

Practically, we don't think that you can do this test without magnification -- i.e. a video-frenzel system with a good enough focus that you can see torsion.

Another method is to use an examining microscope focused on the sclera. We are less enthused about technique as it is very hard to keep the sclera in view while the patient is undergoing a maneuver. Also, the light can be uncomfortable.

For those familiar with posterior canal BPPV, the vector relationships between vertical and torsional components is reversed so that the upbeating nystagmus beats away from the "bad" ear, and downbeating, towards the "good" ear. More commonly, however, no nystagmus at all is produced by either maneuver. In persons with lateral canal fistulae (which are rare and usually confined to persons with cholesteatoma or after fenestration surgery), horizontal nystagmus can be produced (see example below). In persons with window fistulae, generally very little nystagmus is produced by Valsalva or for that matter, any maneuver.

nystagmus elicited by Valsalva in person with L Superior Canal Dehiscence (51 meg)

R SCD nystagmus elicited by Valsalva in person with R Superior Canal Dehiscence -- figure 2b (2 meg)

Fenestration Movie of nystagmus elicited by Valsalva in person with fenestration

 

Tullio testing (i.e. nystagmus from loud noise).

While certainly there can be nystagmus provoked by sound in SCD, the equipment to deliver calibrated intensity sound to each ear in turn is generally not found at the bedside, but rather is found in the audiology suite. In the past, there was a device resembling a children's toy called a "Barany noise box", but these have vanished. We sometimes use a portable audiometer to deliver 500 hZ, 100 dB to each ear in turn. We think that this is generally more trouble than it is worth as the oVEMP test is very effective in detecting sound sensitivity.

Fistula testing (i.e. nystagmus from pressure in the external ear canal).

Our current feeling is that fistula tests are much lower yield than the oVEMP test to be discussed in the next page..

Movie of nystagmus elicited by pressure

Movie2 of nystagmus elicited by pressure in person with R SCD (courtesy of Dr. Dario Yacovino).

A fistula test , which entails making a sensitive recording of eye movements, usually with video frenzel goggles, while pressurizing each ear canal with a rubber bulb, is occasionally helpful to diagnose SCD. A positive test is good grounds for a temporal-bone CT. Fistula tests are little used because they are difficult to do and insensitive. Fistula tests are often not available or even thought of. However, if a patient complains of dizziness during tympanometry, this is a clue that the patient has a positive fistula pressure test.

A strong nystagmus (vertical and rotatory) may be produced by pressure in the external ear canal. However, we do not think that this is very sensitive. It is very specific.

Vibration test for SCD

Vibration
Upbeating nystagmus provoked by vibration over the mastoid of person with left sided SCD.  Image courtesy of Dr. Dario Yacovino.

 

Vibration testing can occasionally produce nystagmus over the defective ear in SCD.  An example of this is shown above.  Our impression is that vibration is insensitive. It is also nonspecific as there are many patients without any SCD that will have vertical nystagmus provoked by vibration. There is some room for disagreement here however, as our impression is that it is insensitive may relate to methodology (we usually vibrate the SCM, not the mastoid), and our impression that it is nonspecific may just be wrong (too few samples).

Pulse synchronous nystagmus in SCD.

Simple observation of the patient's eyes with appropriate equipment (such as video frenzel goggle) may also provide the diagnosis, as in some cases, there is a pulse-synchronous oscillation (Rambold, 2001; Hain et al, 2008), see videos below. This rare but specific sign requires either use of an ophthalmoscope or video frenzel goggles to see it. This sign is specific byt subtle and one also has to think of it (: this is usually the hard part) . If you are watching a pendular nystagmus at about the same frequency of the patient's heart, it helps to take their pulse, and count out each beat while watching on screen.

The main confounding possibility is oculopalatal myoclonus, which causes a similar but non-pulse synchronous oscillation. This is easily checked by looking at the patient's throat. There are also many other rare sources of pendular nystagmus, but almost all of thse have visual or neurological symptoms.

SCD pulse synchronous nystagmus movieSupplemental material: ----Pulse synchronous nystagmus in R SCD

 

See also: SCD (overview)SCD references