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The role of patch testing in genital dermatitis: A less commonly considered etiology

Acta Eruditorum

Abby Van Voorhees

Dr. Van Voorhees is the physician editor of Dermatology World. She interviews the author of a recent study each month.

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In this month’s Acta Eruditorum column, Physician Editor Abby S. Van Voorhees, MD, talks with Peter Schalock, MD, about his recent Dermatitis article, “Genital Contact Dermatitis: A Retrospective Analysis.”

Dr. Van Voorhees: To start out, tell us a little bit about the population you studied.

Dr. Schalock: The population studied was the standard patch test population — people who were referred for evaluation of dermatitis, not the general population. We studied patients identified between January 1990 and December 2006. In the entire database there were 1,238 patients total. Of those only 37 had a genital dermatosis as their chief complaint or as the chief site for their dermatosis. That works out to 2.4 percent of the population we saw during those 17 years.

Dr. Van Voorhees: Do patients who have genital dermatitis have a greater or lesser likelihood of having a positive patch test reaction than a patient who might come in for a more typical contact dermatitis?

Dr. Schalock: That was one of the more interesting findings — allergic contact dermatitis was less common with the genital site specifically. There was a trend toward significance — it had a p value of .0058. Genital dermatitis patients also had significantly fewer actual patch test reactions so it seems that those with genital dermatoses didn’t have contact dermatitis as often as the average patient being evaluated with patch testing.

Dr. Van Voorhees: Did any of these patients with genital dermatoses have a history of atopy?

Dr. Schalock: Patients with genital-site dermatitis were significantly less likely to have atopic dermatitis; that p value was .0047. These patients were less likely to have atopic dermatitis and less likely to have allergic contact dermatitis. In my mind, the take-home point from this is that someone with genital-site dermatosis often has some other diagnosis than allergic contact dermatitis but in recalcitrant patients it’s worth patch testing.

Dr. Van Voorhees: What percentage of patients have a positive patch test when they present with a genital rash?

Dr. Schalock: In terms of just straight numbers, 41.5 percent of those tested had a positive test — but of those, 30 percent of the actual patch tests were relevant, indicating true allergic contact dermatitis as the underlying etiology of the patient’s rash.

Dr. Van Voorhees: The relevance of patch testing is an interesting point. How does the relevance of patch testing in those with genital dermatoses compare to a non-genital-site patient who has a positive patch test?

Dr. Schalock: In our study, of the people who had positive patch tests, 73 percent of reactions seemed causative, which is actually a touch higher for the genital site when compared to other body sites.[pagebreak]

Dr. Van Voorhees: So you’re saying that patients who have a positive patch test with a genital rash, probably a slightly larger percentage of those patients have a relevant patch test so it probably is truly an allergic contact dermatitis?

Dr. Schalock: Right. I think fewer people have positives at that site but the people who do have positives tend to have a higher likelihood of having relevant positives.

Dr. Van Voorhees: What were the most common genital allergens?

Dr. Schalock: The top three were fragrance allergens: Balsam of Peru, fragrance mix one, and Balsam of Tolu.

Dr. Van Voorhees: Did you expect to see fragrances as the most common allergens? Are these just very common exposures? Do you have a theory as to why that might be?

Dr. Schalock: I think fragrances are very common exposures. Many of the things that are used especially in the genital area are highly fragranced. I think if you look at other studies you see fragrance-related chemicals causing problems; this occurs in almost every study we looked at. It doesn’t surprise me at all.

Dr. Van Voorhees: Were those fragrance reactions equally likely in males and females?

Dr. Schalock: Yes, there was no difference with gender for those reactions.

Dr. Van Voorhees: What would you say the limitations of what we know about genital contact dermatitis and in particular this group of patients you were looking at are?

Dr. Schalock: In our study itself, one of the limitations, as with any referral center, is the referral bias. I feel that 2.4 percent is a fairly low frequency, but even with that being said our numbers are comparable to some of the bigger cohorts reported in the literature. I feel like our data is good and makes sense, it’s just lower than I expected — I didn’t expect only 37 patients over 16 years.

Dr. Van Voorhees: Do you think that’s a result of dermatologists not thinking to send patients for evaluation who have genital rashes?

Dr. Schalock: I think that’s definitely part of it. I think people also don’t necessarily bring it up. Many patients suffer genital dermatitis or genital irritation and don’t want to talk about it. Even if you do ask about it, I think of one woman in particular, she didn’t want to tell me anything. Finally she did tell me and I was able to help her because it was actually an irritant. But people just don’t want to talk about genital issues and I think probably part of the other bias that we saw in our study is that people aren’t talking about it to their dermatologist or their gynecologist. There’s a cultural reluctance to discuss these kinds of issues.[pagebreak]

Dr. Van Voorhees: Are there other irritants and allergens we should highlight?

Dr. Schalock: The other thing worth mentioning which I think the North American group saw in their study (Archives of Dermatology 2008: 144:749-55) is that the -caines, benzocaine especially, were significant allergens in the North American group data in the genital area. We had no reactions to benzocaine in our data, something I was completely surprised by. Despite that, the North American group numbers support, in the United States at least, that it’s worth having benzocaine on the radar screen in this area.

Dr. Van Voorhees: What about irritant dermatitis? What role might it play in this situation?

Dr. Schalock: If you look at our final diagnoses the most common was “other dermatoses,” but if you break that out it was essentially lichen planus, lichen sclerosus, atopic dermatitis, and psoriasis. That would be among people who did not have any positive patch test.

Speaking of irritant dermatitis, an important allergen to note in these patients is propylene glycol. In and of itself it is an irritant. This is relevant in genital dermatoses because many sexual lubricants include a significant amount of propylene glycol. We didn’t test for it in this study, but people should be aware of it — I anticipate having data soon that will show it’s worth keeping in mind. It can be an allergen but I think of it more as an irritant, anecdotally. 



Dr. Schalock is assistant professor of dermatology at Harvard Medical School. His article was published in Dermatitis, Vol 21, No 6, 2010: pp. 317-320. doi: 10.2310/6620.2010.10048.