A "placebo effect" can cause a diverse array of symptoms in children when undergoing food allergy testing, according to the results of a study published in the current issue of Allergy. One of these effects is that some patients believe they have had an allergic reaction when they have actually received with the placebo.
This reaction is sometimes referred to as a "nocebo" effect. The more conventional placebo reaction is an improvement of symptoms after receiving an inactive substance rather than the real medicine.
"To date, the occurrence and diagnostic significance of placebo events have not extensively been documented," Dr. B. J. Vlieg-Boerstra and colleagues from the University of Groningen, the Netherlands point out.
To investigate, Vlieg-Boerstra's group conducted a double-blind, placebo-controlled food "challenge," in which a patient is exposed a substance that he is likely to be allergic to. A double-blind study is when the doctor and the patients do not know which is the placebo and which is the real medicine.
The researchers examined the occurrence and features of placebo reactions after 132 challenges in 105 children (average age 5.3 years) who were suspected of having an allergy to cow's milk, egg, peanut, hazelnut or soy. Challenges with a placebo or food were performed on different days with at least a 2-week interval in between.
A total of 17 (12.9 percent) false-positive reactions to the placebo occurred in 17 different children, meaning the children developed food allergy symptoms after being exposed to the placebo. Most of these symptoms (65 percent) were objective, such as rash, hives diarrhea and vomiting. The other symptoms were subjective -- reported by the child but couldn't really be verified.
The researchers conclude that doctors should be aware that some reactions to food allergy challenges may be false-positive, and that these sensitivity tests will need to be repeated.
SOURCE: Allergy, August 2007.
