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Sound clues in mystery affliction  

Credit:  Helen Francombe, The Australian, May 09, 2009, theaustralian.com.au ~~

Imagine leaving your house to go about your day, pulling the door closed behind you, when you suddenly feel like you are on a roller-coaster. You lose your balance, fall over and vomit. And you’re so dizzy you can’t get up for 15 minutes.

Now imagine this happens to you twice or thrice a week, without warning. Throw in the responsibility of looking after a young child and you have the life of Sara Eastway, one of about 40,000 people in Australia who have Ménière’s disease.

The vertigo attacks dominate stage one of the disease, and about half of those affected will be lucky enough to have only occasional attacks, with years of remission in between.

The other half will progress to stages two and three, says Bill Gibson, head of the ear, nose and throat department at Sydney’s Royal Prince Alfred Hospital and director of the Sydney Cochlear Implant Centre.

In stage two, patients have a combination of hearing loss, tinnitus and vertigo attacks. In stage three, many people find the vertigo attacks and tinnitus subside a little, but their hearing is damaged so much they have trouble understanding speech and suffer poor balance.

Ménière’s often first strikes between the ages of 30 and 50, Gibson says.

“They are mostly people with a young family and they then can’t do their job and can’t drive,” he says. “If you are an accountant you can probably keep working, but I have a patient who is a butcher and another who is a school bus driver, and they just can’t keep working.”

Anxiety about when the vertigo might strike is a big problem for many patients, and some are so anxious about having an attack in public they become house-bound, he says.

“They are worried if they go shopping they could collapse on the floor at Kmart vomiting, have to call a friend to come and get them, and explain to store security that they are not totally drunk.”

Eastway agrees the anxiety is a disabling aspect of Ménière’s. “The fear of an attack stopped me doing a lot of things I wanted to do with my son, and really stopped me enjoying my maternity leave: it felt more like an incarceration where I was limited to the four walls of my home,” she says.

Although she had only occasional attacks of vertigo before becoming a mother, unfortunately Sara had a cluster of attacks in the first year of her son Tom’s life. No harm has come to Tom during an attack, but she has certainly been left shaken and anxious about what could happen next time.

“Once when Tom was about eight months old I had an attack while I was reading him a story,” she says. “When I was on the floor and couldn’t move, I could hear him exploring the cupboard under the kitchen sink while I waited for my husband to come home.”

The anxiety also led to the reluctant decision not to try for a sibling for Tom.

“We were quite traumatised by the almighty struggle of that first year and we felt it would be too difficult to manage another baby in those circumstances, and irresponsible – or just impossible – to even think about how we would manage to raise two children if the vertigo attacks were to continue.”

A viral infection is one of various theories about what causes Ménière’s. The underlying cause of the disease remains something of a mystery, Gibson says.

“All we really know is that there is a build-up of fluid in the inner ear in Ménière’s disease,” he says.

A certain amount of fluid in the vestibular system and cochlea of the inner ear is normal, and necessary for balance and hearing.

When these fluids are moved – either by motion or sounds – tiny hairs in the inner ear move and transmit electrical signals to your brain to let your body know where you are in space, or to hear.

There is no cure yet for Ménière’s disease, but some patients’ symptoms are reduced by vestibular suppressant medications such as lorazepam (Ativan), or by reducing the amount of fluid in the body (which reduces the amount of fluid in the ear) with diuretics or low-salt diets.

Surgery can also help some patients, Gibson says. Removing the balance portion of the affected ear can provide relief from attacks for some, although their balance will never be as good as it was with two functioning inner ears, he says.

A lucky discovery about the workings of the inner ear by researcher Daniel Brown may be a turning point for our understanding of Ménière’s disease, he says.

Brown has just returned to Australia after a two-year stint in the laboratory of Alec Salt, a world leader in the study of the workings of the inner ear and Ménière’s disease, and head of the Cochlear Fluids Research Laboratory at Washington University in St Louis, Missouri.

While investigating methods of drug delivery to the inner ear in guinea pigs, Brown and Salt stumbled on an interesting finding that might explain what is happening deep in the cochlea of people with Ménière’s disease.

The cochlea is made up of three tubes wound in a spiral to make a shape resembling a snail’s shell, Brown explains. The middle of the three tubes contains a fluid called endolymph, while the two tubes on either side of it contain a different fluid, called perilymph.

The middle tube does not have any openings where fluid can flow in or out to the outer tubes, whereas the two outer tubes are connected by a narrow pathway at the apex of the cochlea (or the centre of the spiral), called the helicotrema.

Injecting a gel containing medication into the helicotrema didn’t work as a drug delivery system, but the initial disappointment turned to excitement when Brown noticed that when the helicotrema was blocked with gel, the guinea pigs became very sensitive to ultra-low frequency sound that would normally be undetectable.

“People with Ménière’s disease are often bothered by infra-sound, which is created by slow changes in pressure, for example by weather fronts or driving up a mountain,” Brown says.

In recent experiments Brown has showed that the helicotrema normally filters out low-frequency sounds in the ear. If the helicotrema is blocked, the inner ear becomes more sensitive (by about 40dB, or 100 times) to low frequencies below 20hertz.

He believes that in people with Ménière’s disease the middle tube of the cochlea is so distended with fluid that it blocks the helicotrema. When the helicotrema is blocked, the pressure in the two outer tubes of the cochlea cannot equalise as it normally would, and the hair cells are displaced by low frequencies, causing the hearing problems.

Brown plans to explore the effects of helicotrema blockage on the vestibular system, responsible for balance.

He is about to continue his fellowship, funded by the Ménière’s Research Fund, at the University of Sydney, where he plans to trial a simple diagnostic test for Ménière’s disease, based on echoes recorded from the inner ear after various frequencies of sound are applied.

Ménière’s is at present often diagnosed by a process of elimination, ruling out the various other possible causes for the symptoms.

The lack of a simple test for Ménière’s disease has been a significant problem in the past, says Gibson, who has been using MRI as one method of diagnosis. The time, cost and invasiveness of MRI make it a less than ideal test, he says. Gibson will be collaborating with Brown to see if the echo responses match the MRI results, and could be used as a much simpler diagnostic test.

Source:  Helen Francombe, The Australian, May 09, 2009, theaustralian.com.au

This article is the work of the source indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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