Photodermatoses are comparatively rare, and dermatologists may sometimes be reluctant to tackle them, according to Vincent DeLeo, MD, of the department of dermatology at the University of Southern California, Los Angeles, who discussed common diagnoses at the annual Coastal Dermatology Symposium.

“They’re not common bread-and-butter dermatitis, like acne rosacea. Many people feel uncomfortable trying to work out the differential diagnosis when they see someone who comes in with what either the patient or the physician thinks is a reaction to the sun,” Dr. DeLeo said in an interview at the meeting.

“Usually, the best clue is the distribution of the rash or lesion,” which often are on the backs of the hands or on the arms from the sleeves down, he added. “When you see that, you should think of a photosensitive eruption,” and consider a differential diagnosis, using “certain tests, asking questions, and looking at the morphology and distribution of the reaction.”

The most common of the photodermatoses is polymorphous light eruption, which typically occurs in people on vacation, often among those who live in temperate climates and react violently to sun overexposure. “You usually have to rule out things like connective tissue disease by getting serology,” Dr. DeLeo noted in the interview.

In general, these patients either present with a reaction or describe a rash that has since cleared up. When a patient is describing a problem that has disappeared, he or she may have a photo of the reaction on their phone, which can be helpful, he said at the meeting jointly presented by the University of Louisville and Global Academy for Medical Education.

Some photodermatoses are characterized by tell-tale rashes indicative of a connective tissue disease like lupus or dermatomyositis, which can be followed up with biopsy and serology to confirm a diagnosis, said Dr. DeLeo, who is also professor emeritus of dermatology at the Icahn School of Medicine at Mount Sinai, New York. Other patterns, such as blisters on the hands, should prompt tests for porphyria cutanea tarda, which requires a 24-hour urine test to confirm.

But reactions in sun-exposed areas can also be caused by drug-induced photosensitivity and drugs such as NSAIDs, antibiotics, and diuretics, among others, Dr. DeLeo said.

Another common reaction can occur with exposure to photosensitizing plant materials, resulting in blisters combined with altered pigmentation. Most frequently, these reactions are caused by exposure to limes, which contain psoralens that absorb light and produce the reaction. “That is a clinical diagnosis and we can recognize that because, like poison ivy, it is usually a streaky kind of reaction in a distinct pattern. You don’t need [additional] tests for that,” he said. This can occur, for example, after making cocktails, he said, describing an example of parents who had been mixing drinks and then picked up their child. Later, they brought the child to the ED with a hand-shaped rash, and treating physicians contacted social services out of fears of child abuse.

In some cases, patients who present with no rash can elicit the problem. Solar urticaria can produce hives on demand – ask a patient to go out in the sun and return after a few minutes, and a rash will generally appear, Dr. DeLeo advised.

Patients might want to take steps to avoid such problems and there are several options available to do so, Dr. DeLeo noted. There is some evidence of efficacy for photoprotection for an extract from a fern plant found in Central and South America, a product called Heliocare, in a study sponsored by the manufacturer, Ferndale Healthcare (J Clin Aesthet Dermatol. 2015 Feb;8[2]:19-23). Patients can also undergo two or three treatments of phototherapy for 3-4 weeks in advance of a trip in order to “harden” the skin and reduce the chances of an overreaction.

Dr. DeLeo presented a simplified guide to use when considering differential diagnoses in patients with photodermatoses.

  • Solar urticaria occurs quickly upon exposure and is short lived.
  • Polymorphous light eruption usually occurs during a vacation and does not affect the face.
  • A sun-related eczematous rash affecting the face, which recurs, is typically photoallergy to sunscreen.
  • A chronic, severe dermatitis seen in a photodistribution pattern could be chronic actinic dermatitis. The patient should undergo phototesting. A biopsy of a severe case may resemble lymphoma.
  • In photosensitive individuals with an uncertain diagnosis, serology testing for connective tissue disease should be performed to rule out lupus or dermatomyositis.
  • When the patient has a rash in only sun-exposed areas, as well as a history of exposure to photosensitizing drugs, the drug should be discontinued to see if the rash disappears.
  • Porphyria cutanea tarda is diagnosed with a 24-hour urine test that reveals at least five times normal uroporphyrin levels, along with hemochromatosis polymorphisms. Levels of uroporphyrin that are elevated but not five times normal are suggestive of pseudoporphyria.
  • Phototoxic contact dermatitis caused by plants often results in unusual distributions.
  • Hispanic individuals with a photodistributed rash, especially in the presence of cheilitis, may have actinic prurigo.

Dr. DeLeo is a consultant for Estee Lauder. The annual Coastal Dermatology Symposium is jointly presented by the University of Louisville and Global Academy for Medical Education. This publication and Global Academy for Medical Education are owned by the same parent company.