Losing the ability to smell can be devastating, robbing sufferers of the pleasures of food and even leading to depression. But doctors are finding new ways to restore the function
Special to The Globe and Mail
Tuesday, March 6, 2001
From scented candles to aromas wafting out of a bakery, smell is the unsung hero of the five senses. It provides the hints we need to know whether food is fresh or foul, or detect life-threatening dangers such as smoke or dangerous gases. People who lose their sense of smell often find it has devastating consequences. This is what Mick O'Hare discovered in June, 1998, when he got a nasty, feverish cold. It wasn't until about a week later, when he was eating Thai food with his wife, that he realized his sense of smell and taste were totally gone -- he couldn't even sense the salty taste of his own saliva.An infection ravaged both his olfactory receptors and his taste buds. "My doctor told me there was nothing that could be done except wait. Then a succession of ENTs [ear, nose and throat specialists] told me that sometimes it happens, there's no cure, live with it," he said. Some people are born with a defect and are never able to smell. In an Internet forum frequented by people with smell disorders, one woman with no sense of smell writes: "You can't miss what you never had. But I'm curious and frustrated that there is a part of 'normal' life closed off to me."
While the inability to smell is bad enough, other people's reactions aren't exactly sympathetic. "The loss was totally devastating," O'Hare said. "One of the first things a fellow sufferer told me was that it is the only disability where people will openly laugh in your face when you tell them. They do. But it's not amusing, it's dreadful. I found myself on the floor of the toilets at work one day just crying my eyes out with the mental pain of my situation, I was so totally overwhelmed by what had happened."His reaction and sense of hopelessness is not uncommon, Robert Henkin said. The doctor specializes in treating smell disorders, and is director of the Taste and Smell Clinic in Washington. He takes on patients other doctors say are untreatable, and points out there are a wide range of smell disorders. There are treatments available, though many are still considered by the to be experimental. Disorders range from a total loss of the ability to sniff out the world (causes vary from allergic rhinitis to brain trauma affecting the olfactory centres) to what's referred to as "olfactory hallucinations," or smelling things that just aren't there. Some people are simply born never being able to smell (congenital anosmia), and others are mistaken in what they smell (dysosmics) -- such as rotten eggs instead of toast. One dysosmic reports he smells rotting road-kill deer wherever he goes. Chronic smell disorders affect about 7 per cent of the population, Dr. Henkin said. While it is common to have a partial loss of smell when sick with a cold or flu, it normally comes back in a few days. For people who have a chronic loss or distortion of smell, "its devastating, but in a way that's not necessarily obvious." People take smell for granted, and when it's gone, one is plunged into a scentless world.
"Do you have bad breath, do your clothes have an odour that's going to be obvious? If you pass gas, how bad is the smell? If you can't smell, you lose your taste for food, that interest is gone," Dr. Henkin said. If you don't enjoy eating, that puts a real damper on your social life. In fact, many of his patients become less social -- and that can lead to depression. Try to think of social events or holidays that don't involve food or aromas. He considers the loss of the sense of smell a hidden handicap because, on the surface, people look fine. There are dangers to not being able to smell, too. "You can't smell leaking gas or fire," he pointed out. One of his patients died because she couldn't smell the smoke warning that a fire had started. The loss of the sense of smell can stem from damage or changes to any one of the three major parts of the smell and taste system: the brain, the nerves and the receptors.The most common problem is diseases that somehow affect the receptors, small organs that receive the information about taste and smell before it moves on to the brain. These receptors are nourished by proteins that are excreted by various nearby glands. Illness or trauma can impair the production of these proteins. Certain hormones and other proteins are linked to smell, Dr. Henkin said. They're involved in the growth, development and maturation of the receptors, but right now, only a handful of these compounds are known.
Still, identifying deficiencies and treating them can help patients. One of these saliva compounds is gustin/carbonic anhydrase CAVI. In a study of 14 patients found to be deficient in this compound, 10 had smell restored after treatment for four to six months. Patients were treated with a specially formulated zinc medication that stimulates an increased production of gustin/CAVI.
Much of Dr. Henkin's work lies in trying to restore protein production by using drugs such as theophylline (a commonly used asthma medication) or specialized zinc compounds to trigger the gene responsible for enzyme production in the saliva glands. There are a variety of treatments that can be used, but there is no such thing as one fix for all.
Tests must be done to determine the exact cause of the disorder. One test, for instance, examines the saliva for protein and other compounds that are needed for maintaining the health of the receptors. But Dr. Henkin noted that not many doctors order this test because it is still such a new area of research. Other tests might reveal that the loss of sense of smell, and of taste, can even be a consequence of other medical conditions, said Steven Bromley, a neurologist at the Columbia-Presbyterian Medical Center in New York.
After working for six years at the Smell and Taste Center at the University of Pennsylvania, he has come to the conclusion that there is a need for better assessment of smell and taste disorders. There are actually many classes of problems associated with smell and taste abnormalities, he said. A perpetually clogged up nose or sinuses may be something an ENT would deal with. Yet other causes fall outside the ENT jurisdiction, and symptoms could be a sign of liver or thyroid disease, diabetes or other conditions.The loss of smell can be associated with neurodegenerative conditions such as Parkinson's disease, Alzheimer's disease and multiple sclerosis. As well, numerous medications, including antibiotics, antihistamines, lipid-lowering agents and anticonvulsants can be culprits, causing changes or loss in smell and taste. Dental related problems can lead to a decrease in the ability to smell or taste too -- such as gum disease or a severe build-up of cavity-causing bacteria. And as if aging isn't linked to enough problems, over time there is a decrease in sensitivity to smell and taste
Dr. Bromley said there is a need for the diverse areas of research to come together. "Not a lot of people fuse the specialties that need to be fused to really appreciate the subtleties of smell and taste disturbances," Dr. Bromley said. To further investigate smell, Dr. Henkin has done MRI studies on thousands of patients. He points out there are certain regions in the brain that are crucial for olfaction. The MRIs provide brain maps that "tell us where in the brain smell information is processed and differences in degree of activity between normal people and patients with smell loss or distortions. Even better, it gives us clues as to who needs treatment."
More pieces of the puzzle are starting to fit together. For one, when healthy people smell something unpleasant such as old, dead fish, there is more activation on the right side of the brain. Pleasant smells such as peppermint tend to light up the left side. Researchers can't yet say what this means, plus it doesn't address individual responses, such as which side of the brain lights up in that odd person who likes smelling stinky fish?
In people with congenital anosmia, who have never smelled, there is still activation in the smell regions of the brain. This is similar to the fact that vision parts of the brain are active in people who were born blind, Dr. Henkin said.
All this new research is beginning to pay off for patients such as Mr. O'Hare. He experienced a month without any sense of smell. Then some smell and taste returned, but they were severely distorted. After making a couple of trips to Dr. Henkin, he is now getting normal smell back. "I'm now around 70 per cent [recovered] and delighted," he said. The first smell that came back for him was the aroma wafting from a coffeemaker near his desk. "I remember being ecstatic . . . the second thing I noticed was a colleague's perfume. It wasn't even a nice perfume, but I didn't care." The nose doesn't always know.
Smell, like the other senses, depends on the nervous system's receptor cells sending a message to the brain for interpretation. An olfactory disorder occurs when there is a breakdown in any element of this sensory process. Smell, or olfaction, works the following way:
1. Odour molecules travel through the air.
2. The nasal cavity is where the molecules enter the body's system.
3. Olfactory cila are hair-like structures located on the ends of the sensory receptor cells. Located in the mucus layer that lines the walls of the nasal passage, the cilia pick up the airborne odour molecules, and pass the sensory stimuli up along the receptor cells.
4. The olfactory bulb is the meeting point of all the receptor cells, and here neural messages are formed and sent to the brain.
5. The olfactory tract is the pathway that carries the neural signal to the brain.
6. The olfactory areas of the brain, are where the signals are interpreted as odours.
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