Atopic Dermatitis Skin Testing

Filed under: 4 - Atopic Dermatitis

Skin testing is often a valuable procedure in atopic derma­titis as a help in planning treatment. Its value has, however, been greatly exaggerated, too much attention has been paid to it, and harm has been done, particularly in babies and in young children by too rigorous diet­ing solely on the basis of skin tests. What the mother has actually seen happen to the child is more important. Skin testing is a laboratory procedure, and like all other laboratory pro­cedures it must be evaluated in rela­tion to the patient and not by itself.

Too much attention to laboratory tests and too little attention to the pa­tient is one of the defects of modern medicine, and is often carried to an ab­surdity. I saw not long ago a bottle-fed eczematous baby 7 months old whose family had moved to Boston from a large midwestern city. The mother brought with her a typed report of the skin tests that had been done there in a thriving private clinic. Eighty tests had been done by the indirect method, forty-six of which were reported positive. Some of the things tested for were tobacco, camel hair, mustard, cinnamon, allspice, ginger, paprika, garlic, vanilla, straw­berry, and cucumber. This is not an isolated example by any means.

When one sees such things he be­gins to believe that there is as much foolishness in modern medicine as there was in the Middle Ages, and he is not so very far from right.

There is no need of doing a large number of skin tests on a baby with eczema. If he is tested with most of the foods he is eating, plus egg white, and with a few of the environmental allergens to which he is exposed, that is enough. I never do an intracutaneous test until a scratch test has been done first and is negative, and would not do an intracutaneous test with egg white on any baby, no matter what the scratch test showed. It is sometimes desirable to do a few intracutaneous tests with other al­lergens on eczematous babies, as the skin sensitivity is often of low de­gree and the intracutaneous test may be positive when the scratch test is negative. I have not used the in­direct method of testing for over ten years except for investigative work-it is more bother than it is worth. This could be discussed at considerable length-I will simply say that I do not think much of it. As a matter of fact, it is possible to treat most babies who have atopic derma­titis very well without doing any skin tests at all. I find myself doing fewer and fewer, and the patients seem to do about as well as when I was careful to do complete testing on every patient. Older children, whose trouble is likely to be coming from

the environmental allergens, particu­larly pollen and dust, can be under­stood better and treated better if pretty complete testing with the en­vironmental allergens is done.

In a series of 100 eczematous babies under 1 year of age, who gave posi­tive scratch tests to something, the positive tests to foods were as follows:

Egg   white	86	Corn	2
Milk	26	Spinach	2
Wheat	17	Pea	2
Oat	8	Carrott	2
Barley	6	Orange	2
Beef	6	Lamb	2
Potato	4	Codfish	1
Haddock	3	Chicken	1
Tomato	3

Fifty-six gave positive tests to some­thing they were eating, thirty-nine gave positive tests to egg white alone. It must be understood that this series of 100 was not made up of consecu­tive cases-they were all babies with atopic dermatitis who reacted to something; no babies who had nega­tive skin tests were included.

In a series of thirty-eight under 1 year of age, tested by the scratch method with fifteen environmental allergens, only four children gave positive reactions-the allergens were silk, cat hair, and wool. However, in a series of forty-four which had nega­tive scratch tests to dust and feathers, thirty-one had positive intracutaneous tests to dust and twenty-five to feathers. At the time these tests were made the high percentage of positive reactions was surprising to me, and still is. It may be that some of these were irritative reactions, as fairly strong testing solutions were used, but they gave no reactions on normal babies, and in a good many of these babies reagins for dust and for feathers were present as well as posi­tive skin tests.

In older children positive scratch tests to a variety of environmental allergens become more frequent. In a large series the ratio between posi­tive reactions to foods and to environ­mental allergens was 2.5 to 1, in a series of infants under the age of 1 year it was as 20 to 1.

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