Superior Canal Dehiscence (SCD): Diagnosis -- Symptoms and Bedside Tests.

Timothy C. Hain, MD   • Page last modified: July 24, 2021

See also: SCD (overview) SCD bedside diagnosisSCD lab diagnosisSCD radiology diagnosisSCD conservative treatment sSCD surgical treatmentSCD references

Symptoms of an inner ear dehiscence syndrome

Interesting fact: Patients who can "hear their eyes move" almost always have SCD.

Dizziness: in SCD

Usually there is an unsteadiness which increases with activity and which is relieved by rest.

SCD is a type of inner ear fistula. Some people with fistulas find that their symptoms get worse with coughing, sneezing, or blowing their noses, as well as with exertion and activity. This sort of symptom goes under the general name of "Valsalva induced dizziness", and it can also be associated with other medical conditions in entirely different categories --for example, the Chiari malformation, and a heart condition called "IHSS".   Oddly, a recent report suggests that the Chiari is far more common in SCD (Kuhn and Clenney, 2010) than the normal population. We think that this report is likely erroneous.

Pressure sensitivity: (also see this link).

The changes in air pressure that occur in the middle ear (for example, when your ears "pop" in an airplane) normally do not affect your inner ear. When a fistula is present, such as in SCD, changes in middle ear pressure will directly affect the inner ear, stimulating the balance and/or hearing structures within and causing typical symptoms. Pressure sensitivity due to SCD generally causes much stronger nystagmus than pressure sensitivity in persons with round or oval window fistulae, presumably because the pressure stimulus is directly applied to a single semicircular canal in SCD rather than disturbing the inner ear in a less direct way. There are also a very few other conditions that can also cause pressure sensitivity such as Meniere's disease and vestibular fibrosis.

One would think that persons both on CPAP and SCD would have dizziness from the interaction between the two conditions. We do not know of any confirmation of this as yet.

 

Sound sensitivity

In superior canal dehiscence or in persons with fenestrations, it is not unusual to notice that use of ones own voice or a musical instrument will cause dizziness (this is called the "Tullio's phenomenon").

Movie of nystagmus elicited by sound. For other examples see the page on Tullio's

There are also patients who can indicate that their voice sounds louder than normal to them. This is a form of "autophony". More commonly autophony is caused by a patulous eustachian tube, which is another subject entirely. In eustachian tube malfunction, such as the patulous ET, the voice is "boomy", as if in a barrel. This is due to a longer resonant cavity in the middle ear.

Persons with unilateral SCD may have a positive "hum" test. When they hum a pitch, it is louder on one side.

Patients who can "hear their eyes move" always have SCD. Some hear themselves blink. (Bertholon et al, 2017) If the patients noticed this, without reading about it on the internet, it is very specific. Of course, people are suggestible and if they develop this after reading Dr. Google, it is much less reliable. Occasional people can also "hear their eyes move" after acoustic neuroma surgery, presumably due to abberant regeneration. This is difficult to confuse with SCD however.

Other auditory symptoms

Some people experience ringing or fullness in the ears, and many notice a hearing loss. According to Yuen et al (2009), 85% of persons with SCD have auditory symptoms including autophony (40%), hyperacusis to bodily sounds (65%), hearing loss (40%), aural pressure (45%), and tinnitus (35%). What is missing in this report is a comparison to a control group -- our experience with SCD does not bear out Yuen's observations. We think that the main presenting symptom of SCD is pressure or sound sensitivity. We don't find that these other symptoms or signs are generally troublesome.

Clearly there are some patients with hearing loss - -this is puzzling as the damage to the ear in SCD is nowhere near the cochlea.  Perhaps the difficulty in SCD is that the pressure fluctuates too widely because the inner ear is directly connected to spinal fluid pressure through the opening.  This might be a similar mechanism to the "enlarged vestibular aqueduct" syndrome.

Some patients with SCD experience pulsatile tinnitus. This appears to be a variant of autophony.

Bedside tests for SCD.

 

Bedside Tests that may be helpful in the office (Valsalva is the best) are as follows:

Of the office based tests, the Valsalva is the most specific, though insensitive. 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.

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 Supplemental material Movie of nystagmus elicited by Valsalva in person with fenestration

Case example: In the man shown in figures 3 and 4, 10 seconds of straining produced a very powerful torsional nystagmus (and a lot of dizziness).

Other office based tests:

Our current feeling is that these tests are much lower yield than the Valsalva.

A fistula test , which entails making a sensitive recording of eye movements while pressurizing each ear canal with a rubber bulb, is occasionally helpful. 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 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

Asking patients if they can "hear" a 128 hz tuning fork on their wrist, is often positive, but of course this is vulnerable to suggestibility.

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

Vibration can occasionally produce nystagmus over the defective ear.  An example of this is shown above.  Again, our impression is that this is VERY insensitive. It is also nonspecific as there are far more patients without any SCD that will have vertical nystagmus.

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 and case 2. This rare sign requires either use of an ophthalmoscope or video frensel goggles to see it. One also has to think of it (: this is usually the hard part) The main confounding possibility is oculopalatal myoclonus, which causes a similar but non-pulse synchronous oscillation. There are also many other rare sources of pendular nystagmus, but almost all of thse have visual or neurological symptoms.

SCD pulse synchronous nystagmus movie Supplemental material: ----Pulse synchronous nystagmus in SCD

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

Summary:

There are several bedside tests that are somewhat sensitive to SCD. If there is a high suspicion of SCD from symptoms or one of these bedside tests is positive, a laboratory test is usually the n ext step. These are discussed next on this page. SCD lab diagnosis

See also: SCD (overview) SCD bedside diagnosisSCD lab diagnosisSCD radiology diagnosisSCD conservative treatment sSCD surgical treatmentSCD references