MAUI, HAWAII – Polymorphic light eruption is the most common of all the photodermatoses, yet few physicians will ever actually see the rash in their office, according to Dr. Vincent A. DeLeo.
That’s because polymorphic light eruption (PMLE) typically occurs when someone goes on vacation someplace sunny. By the time the patient returns home, the itchy rash is gone. But the history tells the tale, Dr. DeLeo said at the Hawaii Dermatology Seminar sponsored by Global Academy for Medical Education/Skin Disease Education Foundation.
"PMLE is a clinical diagnosis you make when you’ve ruled out photoallergic contact dermatitis and lupus. It’s a diagnosis of exclusion," explained Dr. DeLeo, chairman of the department of dermatology at St. Luke’s-Roosevelt Hospital Center and Beth Israel Medical Center, both in New York.
Dr. Vincent A DeLeo
The salient features of PMLE are that it’s a recurrent rash, which typically erupts several days after – not within minutes of – sun exposure; it lasts for days; and it spares the face.
The face is spared because patients with PMLE gradually become "hardened" to sunlight. The more sun they get on a body part over time, the less likely they are to experience an eruption at that location. The face gets more sunlight than other body parts during everyday outdoor exposure. The rash of PMLE occurs on skin sites that are usually covered in winter, but exposed to the sun in the spring or while vacationing, such as the upper chest and arms.
A study conducted several decades ago among Harvard Medical School students suggested that PMLE affects about 10% of Americans. European studies indicate 21% of Swedes and 15% of U.K. residents are affected. Women outnumber men with PMLE by at least 2:1. The onset of the condition is typically in the 20s among women and somewhat later in men.
The itchy rash is variable in appearance. It can take the form of papules, papulovesicular lesions, or plaques. In the unlikely event the physician actually sees the rash and takes a biopsy, the histology shows a dense perivascular dermal lymphocytic infiltrate.
The differential diagnosis involves photoallergic contact dermatitis and lupus, both of which, like PMLE, feature recurrent, persistent rashes that erupt after a delay in response to sun exposure. Photoallergic contact dermatitis usually affects the face and almost always is due to sunscreens, with oxybenzone the No. 1 culprit. Photopatch testing will confirm the diagnosis. Titanium- or zinc-based physical sun blockers are protective.
It’s important to recognize that oxybenzone and other offenders are also present in shampoos, rinses, and other personal care products in addition to sunscreens, the dermatologist noted.
The plaque form of PMLE looks morphologically like lupus erythematosus (LE). But LE can be ruled out on the basis of negative results for antinuclear antibody, anti-Ro, and anti-La testing.
Because episodes of PMLE are recurrent and predictable, prophylaxis is the best approach. Dr. DeLeo recommended the use of sunscreens containing avobenzone and ecamsule; the combination works better than either agent alone.
If sunscreens don’t work, his top choice is narrow-band UVB phototherapy. "We use it like you would for psoriasis. We give most patients three treatments per week for 3-4 weeks before they go away on their trip. That usually suppresses the eruption. Essentially we’re hardening them," he said.
A product that physicians can expect to be hearing a lot more about is Polypodium leucotomos, an oral fern extract marketed as a sunscreen in pill form. In one recent open-label study involving 57 patients with PMLE, three-quarters of them benefited (G. Ital. Dermatol. Venereol. 2011;146:85-7). In another open-label study by other investigators, this one involving 35 PMLE patients, daily P. leucotomos also resulted in a significant reduction in sensitivity to sunlight (J. Am. Acad. Dermatol. 2012;66:58-62). The usual dosage is 240 mg twice daily.
P. leucotomos has been a commercially available natural product in Europe for 3 decades, with well-established safety. It has been acquired by Ferndale Pharma, which plans to raise its market profile in the United States.
Dr. DeLeo reported serving as a consultant to numerous pharmaceutical and cosmetics companies. SDEF and this news organization are owned by the same parent company.