Are you a rash whisperer?

By Ruth Carol, contributing writer

While patch testing has been the gold standard for diagnosing allergic contact dermatitis (ACD) for a century, the key is combining the patient’s history and clinical examination with the results to determine the relevance of positive patch testing. That means asking the right questions, linking the answers to potential allergens, determining which patch tests are likely to yield the best results, having a good eye, and accurately interpreting the results. Once the offending allergens are identified, it requires educating the patient about how to avoid them. Those who do it well have earned the nickname the “rash whisperer.”

Standard patch tests and beyond

The commonly used patch tests are the Thin-Layer Rapid Use Epicutaneous Test (T.R.U.E. Test), American Contact Dermatitis Society (ACDS) Core Allergen Series, and North American Contact Dermatitis Group (NACDG) Standard Series. The T.R.U.E. Test consists of 36 FDA-approved allergens, the ACDS series is a panel of 80 allergens, and the NACDG series is composed of 70 allergens.

“There are more than 15,000 allergens out there. You’re going to miss opportunities to diagnose ACD if you only test for 36,” said Bruce Brod, MD, co-director of the Occupational and Contact Dermatitis Program at Penn Dermatology and immediate past president of the ACDS. “On the other hand, the T.R.U.E. Test encompasses some of the more common allergens.” It is also commercially available, making it convenient and more cost effective for dermatologists who don’t house allergens for comprehensive patch testing, noted Jonathan Zippin, MD, PhD, vice chair of research and director of the Contact, Occupational, and Photodermatitis Service at Weill Cornell Medicine in New York City.

While allergens in the T.R.U.E. Test do not change frequently, both the ACDS and NACDG series are routinely updated. The ACDS series is a real-world patch testing baseline series that is scaleable, Dr. Brod explained. A consensus group of dermatologists — of which Dr. Brod was a part — compiled suggested allergen groups organized in terms of prevalence that can be logically scaled up or down based on the needs of the patch tester and individuals being tested. The NACDG is a multi-center research group that developed a panel of allergens including some used to study relevance.

Oftentimes, larger panels are needed to comprehensively evaluate patients. Examples of advanced trays that can be ordered include series to detect allergens in corticosteroids, botanical extracts, hair dressing products, rubber, shoes, and textiles. Dermatologists should assess their needs and choose supplemental series based on what would most benefit their patients, Dr. Brod said. Customized panels can help identify exposures that differ based on patient population demographics and geographic distribution. He has a lot of consults for patients prior to having metal implants, so he has a panel for orthopedic metals. Because Dr. Brod sees a lot of health care workers with hand dermatitis, he put together a series of panels to identify allergens in rubber gloves. It is estimated that 21-34% of ACD diagnoses would be missed without testing for supplemental allergens through comprehensive patch testing, added Jenny Murase, MD, director of the Patch Test Clinic at the Palo Alto Foundation Medical Group, and member of the ACDS Board of Directors.

Pros and cons of patch testing

Patch testing, however, is not an exact science. It’s suggested that the T.R.U.E. Test detects 66% of allergens, noted Christen Mowad, MD, director of the Contact and Occupational Dermatitis Clinic at Geisinger Medical Center. With expanded patch testing, that number is more like 80%. Customized panels can raise those numbers even higher.

It’s a very time- and labor-intensive process, especially when patients bring in their own products for testing. Staff has to learn how to prepare the trays and the nurse spends a lot of time with patients on their intake questionnaires. In a private practice, staffing and training would be an issue as would the cost of the tests, not to mention the time it takes for each appointment. “For a private practitioner who sees one patient every 15 minutes, there is not enough time to figure out potential allergens,” Dr. Murase added.

Patch testing is also time consuming and inconvenient for patients, who must come for a visit when the patches are placed on their back, return in two days for a patch reading, and return in five to seven days after that for a final reading. Patients can be itchy and uncomfortable if they have a reaction. Furthermore, some insurance companies have started to limit the number of patches they will cover. Insurance won’t necessarily pay for an additional 70-plus allergens after the patient has already had a T.R.U.E. Test, leaving the patient with additional expenses.

Patch testing is, however, the only thing that leads to a cure for ACD. Topical steroids can relieve the symptoms, but that doesn’t do much good if the patient continues to come in contact with the allergen, Dr. Murase said. Sometimes patients blame the medication for not working when the problem is that they are allergic to the steroid — which can be identified through patch testing.

To date, no other type of test is on the horizon to replace patch testing. A lymphocyte transformation assay has been shown to detect a delayed metal hypersensitivity, but it’s not widely available or covered by insurance, Dr. Mowad stated. Perhaps down the line, genomic studies might predict which patients will be allergic to what allergens, Dr. Brod said.

IMPORTANCE OF PATIENT HISTORY, PHYSICAL

In the meantime, the patient history provides clues to determine what allergens to test for. “This is where the detective work comes in,” Dr. Mowad stated. It begins with the questionnaire that asks about medications and personal care, household, and hobby-related products. Having the patient fill out a questionnaire in advance gives them time to reflect on all the products they use, Dr. Brod added. Past medical history and physical exam offer additional clues.

If the patient is a caregiver, it’s important to find out if it’s for an elderly person, infant, child, or pet as the allergen could be in products they are applying to somebody else’s skin, Dr. Mowad explained. Knowing their job title may not help identify potential exposures but learning what they actually do may. Sometimes the product itself is not the culprit, but what it is being applied with, such as a rubber applicator used to put on eye makeup. Products, and even medications, can cause an allergic reaction, even if the patient has been using them for a long time.

Dr. Zippin works off the patient intake questionnaire. “I discuss everything…their workplace, home, hobbies, who they live with, and where they frequent. One question begets another question,” he said. Dr. Zippin has learned not to shy away from asking questions because “the second you don’t ask a question or don’t delve into some personal detail is when you miss something,” he said. If fragrances are suspect, the incense that the patient’s roommate lights may be the allergen, so it’s not enough to ask if the patient uses incense. Asking questions after the patch test results are known is just as important. Dr. Zippin had a patient who developed a rash on the back of their legs. It turns out that the patient was allergic to a chemical in the cleaning supplies used on the toilet seats at their office. “I would never have come up with that before testing,” he said, “but the results provided some clues that led us to discover how the patient was coming in contact with the allergen.”

Pro tip: Ask questions after the patch test results are known.

Dr. Zippin had a patient who developed a rash on the back of their legs. It turns out that the patient was allergic to a chemical in the cleaning supplies used on the toilet seats at their office. “I would never have come up with that before testing,” he said, “but the results provided some clues that led us to discover how the patient was coming in contact with the allergen.”

Dr. Murase added, “There is no clear, easy algorithm to follow. You take a detailed history and then figure out what is likely to be driving the rash.” Oftentimes, more than one allergen is at play in ACD. One of her patients is a baker who reported having reacted to some shampoos and sunscreens in the past. Dr. Murase tested the patient using a bakery, emulsifier, and sunscreen series. The patient was allergic to one baking ingredient, one fragrance, and one sunscreen ingredient. When the patient stopped using those products, they got better. Using just one supplemental panel may not have cleared the patient’s hands because the patient would still have been exposed to the other allergens, she said. “You also have to have a good eye to rule out ‘look alikes’ during the physical exam,” Dr. Murase added.

Pro tip: Consider using more than one supplemental panel.

One of Dr. Murase’s patients is a baker who reported having reacted to some shampoos and sunscreens in the past. Dr. Murase tested the patient using a bakery, emulsifier, and sunscreen series. The patient was allergic to one baking ingredient, one fragrance, and one sunscreen ingredient. When the patient stopped using those products, they got better. Using just one supplemental panel may not have cleared the patient’s hands because the patient would still have been exposed to the other allergens.

CLINICIAN INTERPRETATION

Expertise in interpreting patch test results is essential for diagnosing ACD. The accuracy of the test is dependent upon the skill set of the clinician interpreting the results, emphasized Dr. Brod. For example, experienced testers know factors that cause variability, so they patch test patients when their skin is less inflamed to minimize the risk of false positives and have patients avoid ultraviolet exposure and topical steroids for four weeks on their back prior to placing the patches. They also follow the proper process steps. Dr. Brod is always skeptical about the accuracy of a patch test when a provider only does the first reading. “Those delayed readings are really important because ACD evolves slowly over time,” he said. Up to one-third of positive reactions can be missed when the second reading isn’t done, Dr. Mowad added.

“The more you do it, the better you get at seeing subtleties and nuances that might be missed by someone who doesn’t perform patch testing that often,” Dr. Murase stated. For example, she now recognizes sister allergens that cross react. She knows that some allergens discolor the skin in a certain way and a pustular reaction to certain allergens can occur in a metal tray, both of which could be misinterpreted as a positive result.

“Contact dermatitis specialists have the experience and skill set plus the infrastructure to handle numerous trays and costs incurred from comprehensive patch testing,” said Dr. Zippin, who is the only dermatologist at Cornell who does patch testing. “The other dermatologists have come to the conclusion on their own that it’s too complicated,” Dr. Zippin said. “Even if they get positive results, they don’t know what to tell the patient effectively to avoid the allergen(s). It’s the same way that I refer to my Mohs surgeon to remove my patients’ skin cancers,” he added.

PATIENT EDUCATION

Explaining what products the allergens might be found in and how to avoid them is as important as identifying them. To that end, ACDS members can access its Contact Allergen Management Program (CAMP) designed to help patients identify personal care products that are free of the ingredients that may cause an allergic reaction. Each list generated is personalized for the patient and the CAMP app allows patients to access their list on their phone. The ACDS is developing a portal for patients and physicians that it hopes to launch in 2019 that will make educational materials and resources easily accessible to patients, said Dr. Murase, who serves on ACDS’s Board of Directors and is chair of the CAMP Optimization Task Force. Similarly, dermatologists can use SkinSAFE to generate a safe products list personalized for their patients, also available on an app. “Providing this type of information to patients is useful and empowering,” Dr. Murase said.

If the allergen is an occupational one, the patient should be given potential strategies to avoid it, Dr. Brod stated. That may include recommending occupational safeguards such as keeping work surfaces clean, or personal hygiene practices, using protective equipment, and properly ventilating the area. For one of Dr. Mowad’s patients, it meant not touching the primroses that were on the table at the restaurant where they waitressed. ACD is one of most common causes of occupational diseases in the U.S., according to the AAD’s Burden of Skin Disease report, but up to half of allergens causing occupational dermatitis are missed, Dr. Murase noted.

Pro tip: Give the patient strategies to avoid the allergen.

According to the AAD’s Burden of Skin Disease report, ACD is one of most common causes of occupational diseases in the U.S. If the patient has an occupational allergen, the patient should be given potential strategies to avoid it. For one of Dr. Mowad’s patients, it meant not touching the primroses that were on the table at the restaurant where they waitressed.

Patients need to understand that not all allergens are created equal; some elicit a very powerful reaction while others elicit a mild reaction, Dr. Brod explained. “That means some allergens should be avoided at all costs, whereas the patient might be able to tolerate some products with very low levels of weaker allergens, even if the patient is allergic to one of them.” Patients should also be taught how to do a “use” test on their skin so they can tell if they will have a reaction before using a product on a widespread basis.

ACD may not be simple to diagnose, but it is rewarding for the rash whisperers. Dr. Brod also finds it very humbling. “I’ve learned that we’re not always good at predicting what the allergen will be prior to patch testing,” he said. “That has taught me the value of performing it.” Dr. Murase reads patch testing differently now than when she started 12 years ago. “I’ve grown to appreciate and respect how complex and subtle ACD can be, and I understand how profoundly a single test can improve patients’ lives.”

Patch test. Identify allergens. Avoid them. If only it was that simple to diagnose and treat patients with allergic contact dermatitis.