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When
Stopping To Smell Is A Problem Barbara
Giurlando's troubles began several years ago after her office was
remodeled and she was suddenly surrounded by new printers, faxes
and copiers that gave off a weird odor that she now thinks was
ozone. All
of a sudden, said Giurlando, 62, who lives in Boston, the smell of
perfumes, deodorants or after-shave became sickening. She couldn't
even read newspapers without feeling queasy from the ink smell. Susan
Rioff, 54, of Lexington has the opposite problem. Seven years ago,
she was thrown from a horse and sustained a severe brain injury
that left her with no sense of smell. Because smell is central to
taste, food also lost its flavor. "You
can stay alive without smelling," she said ruefully,
"but you're missing a lot of pleasures. There's a whole part
of experience that I cannot share. It makes me very sad." By
conservative estimates, 4 million Americans have sustained the
complete or partial loss of the sense of smell, sometimes, as in
Rioff's case, after a head injury, but more often as a result of
aging or Alzheimer's disease. In fact, half of all people lose at
least part of their sense of smell by age 65 and 75 percent do so
by age 80, probably because of lower levels of key brain
chemicals, repeated colds or cumulative exposure to toxins or
medications. Until recently, there was little that doctors could
do to help. Thousands
of others, like Giurlando, develop a hyper-acute sense of smell
that drives them to distraction. One woman became as sensitive to
smells as cockroaches, whose noses are 100,000 times more
sensitive than humans. She could walk around a room and trace by
smell where different people had stood, a
sensitivity that was so disabling she became housebound. Still
others suffer from phantom smells - imagined foul odors such as
that from feces or strong chemicals - that may be caused by nasal
polyps or damage to olfactory or taste nerves. To
those not afflicted, having too much or too little sense of smell
may seem trivial. But as many as 90 percent of people who lose the
sense of smell wind up depressed or anxious, said Dr. Alan Hirsch,
neurological director of the Smell and Taste Treatment and
Research Foundation in Chicago.
And because that loss often means losing the ability to
taste as well, people who lose the sense of smell in accidents
sometimes win multimillion-dollar awards in court cases. The
sense of smell is one of the most ancient parts of our nervous
system, so old that it forms part of the reptilian brain, neural
circuits that evolved eons ago. It is so basic that the sense of
smell is the only part of the human sensory system that has a
direct, neurological link from the outside world to the limbic
system in the brain, which controls fear and other emotions. This
special wiring - a kind of neurological shortcut - is vital to
survival. It allows an animal to detect immediately any nearby
predators, or to avoid other potentially fatal dangers, such as
rotting food. This quick link to the brain also allows an animal
to detect the presence of an eager mate, through odor molecules
called pheromones. The primitive nature of the link between smell
and the limbic system is also the reason why smells can trigger
long-buried memories. Lay
people often assume that there is only one way to detect odors -
by sniffing, or orthonasal olfaction. But there is another way -
retronasal olfaction by which smell plays its central role in
taste, said Linda Bartoshuk, a psychologist at Yale Medical
School. "When
you chew," Bartoshuk said, tiny puffs of air containing odor
molecules "drift up the backward route to the nose. You are
not truly aware that this is olfaction: It's what most people
mistakenly call taste." But,
in fact, there are
only five true tastes - sweet, salty, sour, bitter and umani, a
Japanese term for a savory, delicious taste. All the other subtle
flavors that we can detect are combinations of these basic tastes
plus the sense of smell. Basic
though the sense of smell is, it's only in the last few years that
scientists have begun to understand how it works and how to treat
it when things go wrong. Though
humans can detect thousands of distinct odors, the nose only has
about 1,000 olfactory receptors that lie on specialized nerve
cells lining the top of the nasal cavity, said Linda Buck, a
Howard Hughes neurobiologist at Harvard Medical School. She and
others have recently discovered that particular odors are detected
by particular combinations of these receptors. When
an olfactory receptor captures an odor molecule, it triggers
electrical signals carried by nerves that run from the nose to the
olfactory bulbs inside the brain. Along this path, wispy
projections of these nerves, called axons, pass through a porous,
paper-thin piece of bone called the cribiform plate. Someone
with a head injury sometimes loses the sense of smell because that
bony plate shears off the delicate axons as the brain gets slammed
around inside the skull. This breaks the connection between the
olfactory receptors and the brain, said Marcia Levin Pelchat, a
biological psychologist at
the Monell Chemical Sense Center, a nonprofit research
organization in Philadelphia. If
the shearing of olfactory nerves is complete, there is little that
doctors can do to help. But if some neural connections remain
intact, there is a growing array of drugs that may enhance
whatever sense of smell is left, including in some people with
age-related smell loss, said Hirsch. (So far, there appears to be
little doctors can do for people who lose their sense of smell
because of Alzheimer's disease.) Steroids
may help in some cases, particularly if the problem involves nasal
polyps, benign growths that can cause nasal swelling that blocks
odor perception. Another
approach now being tested in Hirsch's lab is to give patients a
drug called phosphatidylcholine, a drug sold over the counter as
Phoschol, which boosts levels of a brain chemical called
acetylcholine, or ACH. The olfactory bulbs need lots of ACH, which
suggests that increasing ACH might restore the sense of smell. So
far, however, the results have
been mixed. Hirsch is also studying the possible efficacy of zinc,
as tablets to be swallowed. Zinc, which appears to help the
transmission of signals along olfactory nerves, seems to be safe,
he said, though if taken as a nasal spray, it can cause a loss of
the sense of smell. Researchers
are also experimenting with Ritalin - the drug used to quiet
hyperactive children - because it can raise levels of a brain
chemical called norepinephrine, which is important to olfactory
bulb function. Some people with age-related smell loss may also
benefit from sniff therapy, which involves repeatedly smelling a
strong odor, such as that of a banana, every day. In some people,
this kind of olfactory retraining may improve a sagging sense of
smell. For
people like Barbara Guirlando whose sense of smell is too acute,
desensitization training may help. This means learning to pair a
nonoffensive odor, such as pepper, with an offensive one. That
doesn't really change the sense of smell, but does allow people to
be less conscious of the noxious odor. Another solution is to
sniff tubes of peppermint, which also can inhibit the conscious
recognition of the offensive smell. Phantom
smells, or phantosmias, often respond to treatment with
anticonvulsant or antidepressant drugs. In
the future, higher-technology solutions may become available,
including transplantation of neural stem cells. The
bottom line, say those who treat smell disorders, is to see a
doctor if you're troubled about smelling too much or too little.
But there's also something else you can do: Wear your seatbelt in
the car and a helmet if you ride a bike or a horse. You probably
can't avoid losing some sense of smell because of aging
but you can reduce the odds of losing it through a head
injury. Judy
Foreman is a Lecturer on Medicine at Harvard Medical School. Her
column appears every other week. Past columns are available on www.myhealthsense.com..
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