Dizziness, vertigo and nausea are common symptoms of an inner-ear infection. But they can also be signs of a stroke.
For doctors, especially those working in emergency rooms, quickly and accurately making the distinction is vital. But basic diagnostic tools, including the otoscope and simple eye-movement tests, are far from definitive. As a result, many doctors resort to a pricey imaging test such as a CT scan or an MRI. Nearly half of the 4 million people who visit U.S. emergency rooms each year with dizziness are given an MRI or CT scan, according to a study issued last month. Only about 3 percent of those 4 million people are actually having strokes.
For the 25 percent of strokes that restrict blood flow to the back portions of the brain, CT scans are a poor diagnostic tool, according to the study's leader, David Newman-Toker, an associate professor of neurology and otolaryngology at the Johns Hopkins University School of Medicine. "CT scans are so bad at detecting [these strokes] that they miss about 85 percent of them" in the first day after symptoms begin, he said. "That's pretty close to useless." Even MRIs miss almost 20 percent of strokes if the test is done within the first 24 hours.
A new device offers a promising option for rooting out the cause of dizziness: eye-tracking goggles.
The goggles have a motion sensor for the head and a high-speed camera that records eye movements. They connect to a laptop that analyzes how the head and each eye — the camera can record only one eye at a time — move in relation to each other.
"If you pay attention to a few specific eye movements, you can discriminate those who have strokes versus those who have inner-ear problems," Newman-Toker said.
If the eye does not react to a specific head motion with its usual reflex, this signals that the vestibular nerve, which connects the inner ear to the brain, may be inflamed and impaired by an infection.
"It's like a telephone wire getting cut," Newman-Toker said. "The phone goes dead."
If the eye reflex remains intact, the doctor should check for stroke, which affects brain tissue and typically does not reach the vestibular nerve. The best way to check is to use an MRI at least 48 hours after onset of symptoms; this catches 99 percent of back-of-brain strokes.
In March, Newman-Toker and his colleagues published the results of a small study demonstrating the goggles' effectiveness. The team used the device to check for stroke in 12 dizzy emergency room patients; it was accurate in all cases. Half of the patients had strokes, as confirmed days later using MRI. Since conducting that study, the researchers have tested 14 additional patients, and the goggles remained 100 percent accurate.
The goggles are fairly simple to operate, according to Newman-Toker, requiring only about an hour of intensive training.
But Michael J. Ruckenstein, a professor of otorhinolaryngology at the Hospital of the University of Pennsylvania, worries that many practitioners may have trouble using them.
"I don't know that an ER physician or nurse is going to have the technical expertise to apply this test accurately," Ruckenstein said. He wholeheartedly believes in the technology and thinks it has "fantastic promise," but said it isn't yet ready for widespread use.
The device, called ICS Impulse, already in use in other countries, received approval in February from the Food and Drug Administration for assessing balance. But it isn't yet approved for use on dizzy patients in the ER.
While the goggles aren't cheap — they cost about $19,000 — they might save money in the long run by reducing superfluous scans. A single MRI test can cost more than $1,200, while Newman-Toker estimates that goggle exams will cost about $100.