Does SCDS worsen over time if it is not treated?
In many cases, it will stay at a certain level, although it's hard to predict. That very first patient I identified with this disorder back in 1995—whose eye movements were so profound in response to sound that I could see just on the exam that there was something wrong with the superior canal—has elected never to have treatment. His most disturbing symptom was loud noises caused his eyes to move, so he's avoided loud noises.
Other people are more disturbed by the disorder. Some people develop eye movements that follow the rhythm of their pulse, and that's extraordinarily disturbing because you're constantly sensing motion. Another thing that's disturbing to people is hearing their own voice, this sense of autophony. Even a conversational voice reverberates and is uncomfortably loud, causing them to feel motion. The range of symptoms is quite diverse, so therapy has to be tailored to the individual.
Do people get this in both ears?
In about one third of cases it's bilateral when diagnosed. Usually there's a more symptomatic ear, and we treat that ear first (although some have opted to have both ears treated, but not at the same time). In the minority, both ears appear to be equally affected.
How is this treated?
The way we have treated this disorder is to mechanically inactivate the balance canal, to plug it with fascia (the covering of muscle) and tiny chips of bone taken from the patient. It's a tiny structure, so you need only the smallest amount of fascia and chips. We've used canal plugging with success. Bone cement is often used to cover the canal after it is plugged. You'd think that if the problem was the covering being missing, why not just replace the covering? In principle that sounds great. In practice, however, we found that function in the canal is often diminished before surgery, and replacing the covering itself may lead to inactivation of the canal anyway.
A person can function perfectly fine with five balance canals, so we believe the best treatment is to plug the canal. We can selectively inactivate one balance canal without affecting the other balance canals. Superior canal plugging is a procedure that usually takes about four hours and requires patients to be in the hospital for a couple of days. I had worked with that canal-plugging technique in a lot of my basic research, so I was comfortable with it as a surgical technique.
Are there preventative measures that can be taken or tests that determine whether a person is at risk for SCDS?
There are screening tests that can be done. We've seen people in their teens and 20s that have this disorder. If someone is having symptoms that are suggestive of superior canal dehiscence, then the evaluation begins with a physical exam to determine if any of the distinctive signs like eye movements evoked by sound or pressure are present. A vestibular evoked myogenic potential test (a neurophysiological assessment technique to inspect the function of organs in the inner ear) can also show abnormalities characteristic of SCDS. A high-resolution CT scan can also be performed to look at the temporal bones for dehiscence.
You mentioned that 1 or 2 percent of the population could be at risk for SCDS. Do you know how many people are afflicted with this disorder?
Experience with this is relatively new. When we started out, we thought, well, this is probably quite rare. We don't have enough data to give an actual number of people afflicted with the disorder, you can just see from the papers and the cases being reported that it may not be all that rare.
Why are we hearing more about SCDS recently?
It's being better recognized because it's been in the medical literature now. Most major ear centers in the world now have experience with it and are comfortable making the diagnosis. It's also a gratifying diagnosis to make, because you can do something about it. The symptoms seem bizarre—I mean, hearing your eyes move. The first patient referred to me was referred by a psychiatrist because his symptoms were so bizarre that it was clear that something was going on. It's a neat story—there's good science in it and an effective treatment once you've made a definitive diagnosis, and the outcomes tend to be very good. It's the kind of thing you'd like to see more of in medical science: Start out with a mystery, come up with an explanation, develop the right screening tests to make the diagnosis, and then come up with an effective treatment.