Atopic Dermatitis & Occlusion: Positive patch tests don't necessarily indicate true allergy

November 1, 2008

Occlusion in patients with atopic dermatitis causes increased transepidermal water loss (TEWL) and increased regulation of specific inflammatory cytokines, according to one study. The findings suggest positive patch tests in atopic dermatitis patients may not necessarily indicate true allergy.

Key Points

Montreal - Patients with atopic dermatitis have increased transepidermal water loss (TEWL) and increased regulation of specific inflammatory cytokines, due to occlusion, according to a recent study.

"We know that one of the primary triggers in atopic dermatitis is barrier dysfunction," says Susan Nedorost, M.D., a dermatologist in Cleveland and associate professor, department of dermatology, University Hospitals Case Medical Center, Cleveland.

"One of the possible (treatment) approaches is to see if we can smother it and make it better," she says.

Dr. Nedorost says that patients with atopic dermatitis find undergoing a patch test to be challenging because of persistent itch. In contrast, patients with psoriasis do not have similar complaints about itch.

"Clinicians who patch test patients with atopic dermatitis will see that these patients will call at midnight and say they can't leave the patches on their back," Dr. Nedorost says.

Likewise, many atopic dermatitis patients cannot tolerate ointment vehicles.

"Psoriasis patients complain about the mess of the ointment, but they don't complain that it makes them itch," Dr. Nedorost says.

Research has begun to investigate why patients with atopic dermatitis are intolerant of occlusion, according to Dr. Nedorost. "It raises the question of whether it is an inflammatory problem," she says.

Fabrics a factor

Anecdotally, patients with atopic dermatitis, particularly children, complain about the fabrics they wear that cause itch, noting some fabrics cause more itch than others.

Dr. Nedorost and co-investigators sought to evaluate how patients with eczema responded to exposure to polyester and lyocell fabrics, occlusive polyethylene wrap and sodium lauryl sulfate. They measured TEWL and inflammatory cytokine and chemokine mRNA produced by the skin in response to these materials.

Study parameters

The team examined six patients with eczema who wore T-shirts that were split vertically into polyester and lyocell for four days, as well as occlusive wrap and sodium lauryl sulfate patches that were taped to the skin. They took TEWL measurements at study entry and then later compared those measurements four days later.

They chose specific cytokines and chemokines to measure, including mRNA for IL-8, IL-1 gamma and IL-1RA, which were obtained through tape stripping the skin.

Researchers also measured the 18S rRNA housekeeping gene. They employed real-time polymerase chain reaction (PCR) to quantify the data.

They observed marked increases in TEWL via polyethylene occlusion and occlusion with sodium lauryl sulfate at four days. Moreover, they observed that occlusion with polyethylene induced IL-8 and IL-1 gamma levels comparable to or in excess of sodium lauryl sulfate.

Additionally, they found the anti-inflammatory IL-1RA was down-regulated through occlusion relative to sodium lauryl sulfate in some patients, whereas few cytokines were induced by polyester and lyocell.

Bacterial proliferation

Dr. Nedorost hypothesized that the production of abundant bacteria might explain the skin irritation associated with occlusion.

"Atopic patients can be prone to bacterial proliferation when you occlude the skin, and that might explain the inflammation," Dr. Nedorost tells Dermatology Times.

In addition, perspiration, increased temperature or other factors may also contribute to the irritation.

Although the study's sample size was small, Dr. Nedorost says the research has implications for clinical practice. Indeed, the findings highlight that positive patch tests may not necessarily be indicative of a true allergy.

"You need to be careful when you interpret positive patch tests in atopic patients, which is especially true in children," she says.

"Many have underlying atopic dermatitis. When evaluating for dermatitis under a percutaneous delivery patch, dermatitis due to occlusion should also be considered as a culprit in addition to reaction to an active drug or component of the adhesive patch," Dr. Nedorost says.

The data suggest that patients with atopic dermatitis would benefit from the use of non-occlusive vehicles, Dr. Nedorost says, noting that other forms of occlusion, apart from polyethylene, can trigger a similar reaction in atopic dermatitis patients.

Disclosure: Lenzing, an Austrian fiber company, sponsored the study.

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