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Shedding light on diagnosing photosensitivity diseases.

SNOWMASS, COLO. -- Photosensitivity diseases can often be confused with other dermatologic conditions, but a few key observations can often shed some light on a correct diagnosis, according to David R. Bickers, M.D.

Photosensitivity diseases fall into three main categories: idiopathic, exogenously induced, and endogenously induced, Dr. Bickers said at a clinical dermatology seminar sponsored by Medicis.

The most common type of idiopathic photosensitivity is polymorphous light eruption (PLE), which presents as delayed erythema, edema, and pruritic papules and plaques on exposed skin.

The condition can sometimes appear on unexposed skin as well.

This condition is most commonly found in women (80% of cases), with onset usually by age 30 years. PLE typically occurs after the initial seasonal exposure to sunlight, explained Dr. Bickers, professor and chair of the department of dermatology at Columbia University, New York.

"One of the key differential diagnoses is to distinguish PLE from airborne contact dermatitis," Dr. Bickers said, adding that the best clue to this is in a careful assessment of the patterns of involvement.

"PLE is less common on the face than on the arms and chest," Dr. Bickers said at the seminar. "If it is on the face, the anatomic areas that are shadowed may be spared, while they will not be in contact dermatitis."

PLE-involved areas may include the neck, upper chest, and dorsal hands, while spared facial areas include the intranasal, retroauricular, and submental areas, as well as the upper eyelids, he reported.

The treatment for PLE involves sunscreen prior to exposure and mid- to high-potency corticosteroids for patients who have already been exposed, Dr. Bickers said at the seminar.

Systemic options include antimalarials, thalidomide, and corticosteroids. Phototherapy can be used as a prophylaxis to desensitize the patient prior to exposure.

Exogenously induced photosensitivity diseases include phototoxicity and photoallergy.

Phototoxicity can occur in anyone who has been exposed to photosensitizing drugs and light exposure, but photoallergy is limited to individuals who have been sensitized to a substance that is activated by light, Dr. Bickers said.

Drug-induced phototoxicities can be caused by psoralens, porphyrins, antibiotics, and NSAIDs. This reaction presents as exaggerated erythema with desquamation and subjective burning and stinging.

Photoallergy, however, presents as eczematous dermatitis and subjective pruritus and should be confirmed with photopatch testing, Dr. Bickers said at the seminar.

One small difference between the presentations of these conditions: Earlobe involvement is usually a sign of photoallergy and not phototoxicity, Dr. Bickers added.

Endogenously induced photosensitivity can be caused by porphyrias, which are present as a result of conditions such as porphyria cutanea tarda, Dr. Bickers explained.

Enzyme deficiencies in cutaneous porphyrias cause the release of excessive amounts of porphyrins. Porphyrins are potent photosensitizers, Dr. Bickers explained, and they make "the skin an innocent bystander in events happening elsewhere in the body."

BY KATE JOHNSON

Montreal Bureau
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Title Annotation:Dermatology
Author:Johnson, Kate
Publication:Internal Medicine News
Geographic Code:1USA
Date:May 1, 2005
Words:468
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