Patch testing can prove very useful in patients with suspected sensitization to a variety of allergens contained in personal care products and orthopedic implants.
Patch testing can prove to be very helpful in determining the source of the rash in patients with a suspected allergic contact dermatitis (ACD), however, clinicians must learn to be savvy as to when, and in which cases, to employ this very useful diagnostic tool.
Allergic contact dermatitis can occur at any age, and the current conventional wisdom is that, in general, everyone with recurrent or persistent dermatitis suspected of having a component of ACD should be patch tested. There are a multitude of potential causes of ACD which can often be due to a variety of ingredients contained in the personal care products used by patients.
“The typical consumer may apply more than 30 lbs of personal care products to their skin a year, and while an average adult female applies 12 personal hygiene products daily—exposing her to 168 discrete chemicals—the average male uses 6 personal care products daily with 85 new unique ingredients,” said Luz S. Fonacier, MD, immediate past president of the American College of Allergy, Asthma & Immunology (ACAAI), professor of medicine, New York University (NYU) Long Island School of Medicine, and head of allergy and training program director, NYU Langone Hospital-Long Island, who recently spoke at the ACAAI annual scientific meeting held November 4 to 8 in New Orleans, Louisiana.1 “These chemicals and ingredients can potentially be the cause of ACD and, as such, should be appropriately investigated and patch tested when suspected.”
An accurate history of personal care product use is also crucial in uncovering the potential source of the ACD. According to Fonacier, many patients empirically change the products they are using on the involved area of ACD presuming that if the dermatitis persists, the products discontinued were not the cause. However, it is likely that the new product contains the same allergen as the original. Fonacier stressed that a detailed history and meticulous surveillance of products used or eliminated are very important in finding the source of the ACD.
Although clues to the cause of ACD can be suspected from the distribution on hands, face, and feet, he said that up to 20% of ACD cases manifest as generalized or scattered rashes, further underscoring the diagnostic importance of patch testing. According to Fonacier, patch testing should be considered in patients with chronic eczematous dermatitis, persistent or recalcitrant dermatitis, occupational dermatitis, hand, leg, or foot dermatitis, stasis dermatitis, AD patients who fail to improve, facial dermatitis (eyelid), and dermatitis with unusual distribution.
“It is important to carefully eliminate the false positives and false negatives when reading results, however, you do not want to over interpret outcomes either,” Fonacier said. “Once you have your positives, you need to determine how relevant the result is in respect to the patient’s symptoms, history, and exposure.”
After allergens are identified from a patch test, patients need to review their personal products and eliminate those that contain the tested allergens. This process can be very challenging and intimidating for patients, Fonacier said, which could lead to compliance issues regarding allergen avoidance.
Databases generating a list of allergens to avoid, along with a comprehensive list of skin care products that are free of their identified allergens, increase patient compliance and can lead to faster resolution of clinical disease. According to Fonacier, the cycle of an ideal patch testing procedure is to identify the allergens, determine the relevance, educate patients, and then offer them treatment and management alternatives.
To help improve compliance of allergy avoidance, there are currently 2 computer generated databases available in the United States that list products free of allergens which the patient is allergic, and can safely use, including the Contact Allergen Management Program (CAMP) available for members of the American Contact Dermatitis Society, and Mayo Clinic’s Contact Allergen Replacement Database (CARD).2,3
Hypersensitivity reactions to orthopedic implants exist and remain a controversial field in contact dermatitis and patch testing. Unfortunately, the value of patch testing and the diagnostic clarity one can achieve are not fully recognized across all specialties, he explained.
“One of the main challenges in patch testing today is that many orthopedic surgeons still do not recognize that metal hypersensitivity to implants can cause joint replacement failure, and that patch testing can be useful in identifying allergic hypersensitivities to metal prostheses. Some orthopedic surgeons have been taught that an allergic reaction to implants constitutes less than 1% of joint failure cases, or that patch testing does not reflect the immune setting in the joint and therefore [it] can’t be trusted. The standard of care needs to change so that all clinicians understand the diagnostic value of patch testing in the right circumstances,” said Karin Pacheco, MD, MSPH, an assistant professor in the Department of Medicine, Division of Environmental & Occupational Health Sciences, National Jewish Health, Denver, Colorado, who spoke at the ACAAI meeting.
An allergic reaction to an implanted metal can range from mild irritation or rash of the skin over the implant, to pain and tenderness in or around the implant. In severe cases, an implanted joint can loosen and become unstable. A system-wide rash is rare.
Current orthopedic literature addresses what to do with joint failure, Pacheco said, but the 10% rate of joint replacement failure hasn’t changed much over the last 20 years. The common causes that an orthopedic surgeon will consider are infection or malposition of the device. However, according to Pacheco, it is important to recognize that sensitization to implant components is another important cause of joint failure.
“The patients we see are referred by their orthopedist and have already been evaluated for possible infections or mechanical issues and, in that setting, our rates of relevant patch test results are high with approximately half of our patients showing sensitization to something in their joint,” Pacheco said. “So, it is important to consider the diagnosis, do the right patch testing, and then correlate the results with the actual implant components.”
Interestingly, most orthopedic implant manufacturer websites do not list what the implants are made of, making it even more challenging to uncover the potential source of its allergic hypersensitivity.
The majority of orthopedic implants are made of cobalt chromium with a small amount of nickel and have undergone significant research and development resulting in very good mechanical properties, she said. In cases of suspected ACD, clinicians should investigate whether the patient is sensitized to something in the common implant makeup, then clarify whether they are sensitized to something in their specific implant. For this, clinicians should use a standardized panel that incorporates all the metals included in different implants today, as it could hold the answers to these important questions.
In terms of preoperative patients, it is reasonable to test those with a prior history of reactions to metal or methacrylate products such as in artificial nails. Nevertheless, most patients without previous history of allergic reactions are not commonly tested before the initial implant, she said, because without it, results would be hard to interpret.
“We not only need to publish more papers demonstrating that, in the right patient, patch testing can make a huge difference in their outcome, but we also need to get other specialties on board and stress the diagnostic importance and benefits of patch testing in the right case scenarios,” Pacheco said.
Fonacier and Pacheco reported no relevant disclosures.
1. Fonacier LS, Pacheco K. Pearls and pitfall of patch testing for contact dermatitis and biomedical devices allergens. Presented at: ACAAI 2021 Annual Scientific Meeting; November 4-8, 2021; in New Orleans, LA, and virtual.
2. Contact Allergen Management Program. American Contact Dermatitis Society. Accessed November 3, 2021. https://www.contactderm.org/resources/acds-camp
3. Contact Allergen Replacement Database. Mayo Clinic. Accessed November 3, 2021. http://allergyfreeskin.com