Rapid, uncontrollable eye movements that swish and thump as the eyes roll and blink. Bones that creak as the body moves. Sudden dizziness, loss of balance. Falling down after a loud noise, such as the sound of your own voice, a cough or even laughter. These are hallmarks of a debilitating and relatively rare syndrome known as superior canal dehiscence that has stumped clinicians for a long time.
Victims lose balance, fall down stairs, are unable to read or sleep due to loud noises inside their head, and some become convinced they are mentally ill, suffering from symptoms that won't yield to conventional treatment. Now, Johns Hopkins surgeons have proven that these symptoms can all be successfully treated by a single operation that plugs up a threadbare layer of bone in the inner ear.
Superior canal dehiscence occurs in roughly equal numbers of men and women and is often not diagnosed until after age 40, when symptoms, such as hearing loss, appear to worsen. However, patients often recall that initial symptoms happened much earlier in their lives.
"The surgical plugging procedure can put a stop to even severe symptoms and can lead to a return to normal daily activities and, in some cases, to a mild-to-moderate improvement in hearing," says Lloyd B. Minor, M.D., the Andelot Professor and director of otolaryngology - head and neck surgery at The Johns Hopkins University School of Medicine. It was Minor who, in 1998, first clinically described superior canal dehiscence and developed the surgical techniques to repair it.
In a pair of reports believed to offer the largest followup analysis of patients after their surgery for the syndrome, a Hopkins team, led by Minor, found that plugging the superior canal where the bone casing is thin, and then covering the plug with a bone graft, prevented symptoms from recurring.
Researchers say that for patients who had already experienced some hearing loss from the syndrome, the plugging procedure - which essentially compresses and closes off the canal - often helps restore their hearing. They note that improvements in hearing occurred in five of 29 patients who underwent surgery for the disorder between 1996 and 2005.
They add that the risk of hearing loss is very low in patients who have not had previous ear surgery, with no hearing loss reported in 19 patients undergoing their first operation.
No wider than a toothpick, the canal bone in question rests at the top of the inner ear's three semicircular canals. Thinning due to failure of bone to develop properly and maintain its strength over time makes the ear hypersensitive to sound and motion. A common complaint is autophony, where patients hear their own voices reverberating inside their head. For some patients, even a conversational level of loudness can produce symptoms strong enough to cause severe discomfort.
The Hopkins surgeons will present their findings from a decade's worth of research this week at the Combined Otolaryngological Spring Meeting (COSM) being held in Chicago, Ill. Since the team saw its first patient with the condition in 1995, they have successfully operated on 39.
While no survey exists of just how widespread is the condition, Minor says about two-thirds of those who have it will never require surgery. But for the remaining one-third who undergo surgery to repair the bone casing in the ear, the surgery in most cases fixes the disturbance in balance caused by the dehiscence.
In their latest findings, researchers report that in 19 patients undergoing analysis of abnormal eye movements, surgery led to a resolution in each case of vertigo, or dizziness, brought on by loud noises.
The surgery, which takes from four to six hours, is extremely delicate and requires access to the inner ear, a space the surgeons describe as no wider than the diameter of a dime. They first cut a hole above the ear and open the skull, after which they move aside a part of the brain so that they can reach the three paired canals that form the inner ear, of which the superior canal is the one closest to the top of the head. The plug mixture is made up of small chips of the patient's bone and fibrous tissue taken from the area of incision and the temporary opening the surgeons make in the skull.
In the first study to be presented at the COSM, audiograms were performed both presurgery and postsurgery to assess hearing levels. In the second study, tests of eye movements in response to sound and to rapid head movements were used to assess the inner ear's balance function after surgery.
Minor cautions that the surgery has the potential to damage balance, but notes that the studies suggest the other two balance canals, the posterior and horizontal canals, can adapt. Postsurgery results showed a 44 percent reduction in the function of the superior semicircular canal, while function in the other two canals was typically not affected. This shows, researchers say, that plugging typically limits sensation in just the one canal.
The results should allow surgeons to better counsel their patients with superior canal dehiscence on what is the likely improvement to their hearing and balance after either procedure, according to the lead authors of the studies, John Carey, M.D., an associate professor, and Charles Limb, M.D., an assistant professor, both in otolaryngology - head and neck surgery at Hopkins.
However, Limb notes that only long-term data from postsurgical monitoring of patients for longer than 10 years will truly confirm if surgical treatments hold steady or decline at some point. The Hopkins team continues to monitor how its patients are doing.
Although research on the condition is relatively new, Minor believes the underlying cause of the syndrome is an opening in a layer of bone that fails to develop to normal thickness during or after birth. The open balance canal can then respond to sounds and to pressure induced by activities such as coughing, sneezing or straining. And this abnormal activation of the canal is then misinterpreted by the brain as a head movement that leads patients to lose their balance and to have abnormal eye movements.
According to Minor, normal inner ear bone thickness is on average 0.7 millimeters. And while the condition can affect both ears, in patients with just one ear affected, the other ear has less-than-normal bone thickness.
Diagnosing the condition consists of CT scans of the head to gauge the thickness of the bones in the inner ear, as well as balance tests to record how various sounds trigger body motions, including eye movements and contractions of muscles in the neck.
Funding for this study was provided in part by the National Institute on Deafness and Other Communication Disorders, a member of the National Institutes of Health.
In addition to Minor, Carey and Limb, other researchers involved in this research, conducted solely at Hopkins, were Americo Migliaccio, Ph.D., and Sharmila Srireddy, M.S., M.A.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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