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Victoria,
BC-- Patch-testing relevance reflects the knowledge base of
the physician, said Frances J. Storrs, MD, professor emerita, Oregon
Health and Science University, Portland.
While some may beg to differ, Dr. Storrs draws a big distinction
between an allergy, which is a disease, and an allergic patch test
reaction, which is not.
"One can be allergic to gold, but not have an allergy to gold.
It's confusing, but I think there is an important difference,"
she said at the annual meeting of the Canadian Dermatology Association.
Irritant
or allergen?
Positive patch tests to gold are very common. However, many patients
who have a positive test have no difficulty wearing gold, either
in their fillings or in their jewelry. Dr. Storrs recruited 136
of these patients for a study and found that 24 of 71 people who
had gold in their mouths had positive patch tests. Sixty-five people
who wore gold jewelry (no gold in their mouths) had positive patch
tests. "There was a much higher positive rate if they had gold
in their mouths," she said, "but it looks like the gold
seldom reached the level where it caused a real allergy."
Positive patch test reactions to dust mites are also very common.
In Dr. Storr's opinion, some poorly conducted research was done
on this and as a result dust mites are getting bad press for driving
or causing atopic dermatitis. The conclusion is likely over-rated,
she said.
Definite
relevance
Definite relevance means that a patient has a positive patch test
along with a positive reaction to a product or object. For example,
a 72-year-old woman had a knee replacement in 1999 with a metal
alloy and acrylate glue. Her knee pain returned two years later,
with a dermatitis over the incision line. She was negative to a
metal tray, including nickel. Subsequently, she tested positive
to tea-tree oil and two other fragrances. Even though she used tea-tree
oil on other parts of her body, she came up positive only to the
tea-tree oil that was put on her knee.
"So we had a positive allergen, we tested her own product,
and it got better when she stopped using the product."
Probable
relevance
Probable relevance means that a patient has a positive patch test
and it is discovered that the allergen is in something that the
patient is using. For example, a patient with long-lasting dermatitis
on the face had positive patch-test reaction to an ingredient in
her moisturizer. When she stopped using the product her symptoms
disappeared. This was a clear case of probable relevance because
she was not tested to the moisturizer.
Possible
relevance
Possible relevance means there is a positive patch test and the
allergen, though not found, could be present in the patient's environment.
For example, the prevalence of fragrance-mix patch-test reactions
is high. Dr. Storrs believes many of them to be irritant reactions,
and these can be difficult to separate from allergic reactions.
"Seldom, if ever, are these reactions analysed to see if the
patient actually has a dermatitis to any perfume that goes away
when the perfume is taken away. Instead, there is a dermatitis and
the patient has what is read as a positive reaction to fragrance
mix. Whether a fragrance in the patient's product actually caused
the dermatitis is almost never investigated. I think true fragrance
allergy is vastly over-rated."
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