With VNG, if the patient is sound-sensitive, you can use a loud sound and look for eye movement, he said. If you get that, you can send them to get an x-ray or high-resolution computed tomography [CT]. Tell the radiologist that you suspect superior canal dehiscence and ask for a thin-cut CT with bone windows and ask the radiologist to reconstruct in the plane of the superior canal because you’re looking for a hole.
Explore This IssueApril 2006
He added that otolaryngologists should suspect this underlying cause for the dizziness if the patient complains of dizziness, is sensitive to sound, and the CT shows that there is no bone in the area.
Identifying this cause can spare such patients unnecessary surgery for suspected fistulae, he said. Migraine-related dizziness can be identified with questions regarding light sensitivity.
Specialty Clinic Tests
Because of the costs of the equipment, all of the experts interviewed agreed that some of the more advanced tests, such as the rotary chair test, are most appropriately performed at referral clinics.
It’s a select group of people that need the rotary chair test, Dr. Goebel said. That group includes those who don’t have caloric responses and those with a unilateral vestibular function loss. Another group would those with a unilateral loss, but with an unknown amount of central nervous system compensation.
Rotary Chair Tests
The rotary chair test involves the patient sitting in a chair, head affixed to a head holder and using video goggles as with VNG. The testing system uses software to lock on the pupil for a tracing of the eye movement and calculates how well the patient’s system is making eye movements when moving to the right or left.
A variation of this, eccentric rotation, utilizes asymmetric stimulation of the inner ear, particularly the utricle. This test may be the first to give an idea of utricular function, Dr. Goebel said.
Noting that the standard rotary chair has limitations regarding speed, Dr. Epley pointed out that he has developed the Epley Omniax chair, which is manufactured by Vesticon, to address these limitations and to allow for a fuller positional test. Since patients with cupolalithiasis have vertigo in some positions but not in others, the Omniax chair puts patients in all of the positions, he said. The chair is still being reviewed by the Food and Drug Administration.
Because rotary chairs can be costly, in the neighborhood of $100,000, others are using a less costly device: a computerized headband that can measure acceleration of eye and head movement in horizontal and vertical planes.