Okay, so never say never in medicine, but just like all the “who done it movies” no matter how much they try to make you believe it’s the butler, it’s never the butler.
Dermatitis/Eczema is listed as a diagnosis code in about 9 percent of all dermatology office visits, and allergic contact dermatitis accounts for about 20 percent of those visits. Regardless of your specialty, most practices will encounter patients with contact dermatitis. In some cases, the cause is easy to determine, for instance, a rash where EKG electrodes were placed or an eruption everywhere medication patches were located. However, any dermatologist will tell you the number one item patients tend to blame for any rash of unknown cause is laundry detergent. Now mind you most folks have already changed their detergent weeks before they see you and the outbreak remains, yet the soap still gets the blame. This experience is why I disagree with one of the famous quotes of Sir William Osler “Listen to your patient, he is telling you the diagnosis” he should have said, “Listen to your patient unless you are a dermatologist.”
Contact dermatitis generally falls into two classes – it is either irritant or allergenic. Irritant contact dermatitis is more common, but both conditions are difficult to differentiate by appearance. Even biopsies of the skin frequently cannot distinguish between the two disease states. An old mentor once told me “I can easily tell allergic contact dermatitis from irritant contact dermatitis just by looking and I only get it wrong half the time.”
Many times you can find irritant and allergic contact dermatitis colluding together especially in the case of hand eczema. Mild allergic sensitivity to a fragrance or preservative in a soap combined with repeated irritation from frequent hand washing, common to many professions, can result in a whopping dermatitis. Sorting out the causes can be a Sherlockian task.
Hundreds of chemicals can cause allergic contact dermatitis, which can be a bit of a nightmare in trying to determine the source. Complicating the diagnosis further, it usually takes multiple repeated exposures over time before someone becomes sensitized to an allergen. Personally, I am a perfect example of this phenomenon. For years I wore swimming goggles with neoprene rubber seals then one day I began breaking out with bilateral eyelid dermatitis. Switching goggles to a silicon seal solved the problem, but any change back to the neoprene seal resulted in me looking like Rocket raccoon from the Guardians of the Galaxy. It took over ten years of exposure for me to develop the sensitivity. One exception to long-term exposure causing sensitivity is poison ivy. With a single exposure to the urushiol resin, there is about an 80 percent conversion rate to allergic sensitivity. So nobody breaks out with the first exposure to poison ivy as an immune response has not developed, this is your one freebie, but after that watch out.
Fortunately, ninety-five percent of allergic contact dermatitis in the United States is limited to about 100 or so more common allergens. The remaining five percent includes thousands of chemicals, but a person is less likely to receive exposure to these compounds in the general population. So the trick is how does one sort out what chemical the patient has become allergic to. In 1884 Dr. Jadassohn applied some chemicals to blotting paper, which he then affixed to the skin. This produced a reaction similar to the eruption the patient was experiencing (the term allergy had not been created yet). Jadassohn’s experiment was the first patch test, and not much has changed in testing for allergic contact dermatitis the last 134 years. The good news is that you could have slipped on reading your medical journals for a few decades only to find out that your patch testing skills don’t need updating. The bad news is patch testing remains a tedious, labor-intensive process, which requires multiple days to determine a diagnosis.
Many physician’s offices can easily do patch testing now with premade patch test panels called T.R.U.E Test ®. This test contains 35 different allergens and is FDA approved for use in the United States. The only problem I have with this test is that the limited number of allergens can result in missing a significant percentage of positive reactions. Some dermatologists will do their testing using the allergens from the North American screen. This panel includes approximately 80 allergens; additionally, there are specialized panels such as shoe series, dental series, metal series, hairdresser series, etc. When positive reactions are noted, physicians who are members of the American Contact Dermatitis Society can access the Contact Allergen Management Program which can create personalized, safe product lists for patients once their allergens are identified.
Imagine a wealthy patient comes in with a pruritic recurrent eczematous on both arms that has been persistent since the beginning of summer. His biopsy shows a spongiotic dermatitis with a differential of chronic allergic contact dermatitis, chronic irritant dermatitis, or idiopathic eczema. My recommendation for you would be if you think it might be allergic contact dermatitis, patch test, and if you don’t think it’s allergic contact dermatitis, patch test. The patch test results show a 2+ positive reaction to Benzocaine, which is found in his anti-itch cream that he has been using the last three months. He is surprised because he was sure it was due to his butler changing the laundry detergent. He states but I have used this cream for years without problems. You respond in the words of the famous French detective Jacques Clouseau “Not anymore.”
By: Lucky Meisenheimer, MD and John Meisenheimer, VII
Contact dermatitis trivia: The most common allergen for contact dermatitis in the United States is Nickel. The most common iatrogenically associated allergen is neomycin.