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Photoallergic contact dermatitis (PACD), a subtype of allergic contact dermatitis that occurs because of the specific combination of exposure to an exogenous chemical applied topically to the skin and UV radiation, may be more common than was once thought. Although the incidence in the general population is unknown, current research points to approximately 20% to 40% of patients with suspected photosensitivity having a PACD diagnosis. Recently, the North American Contact Dermatitis Group (NACDG) reported that 21% of 373 patients undergoing photopatch testing (PPT) were diagnosed with PACD; however, PPT is not routinely performed, which may contribute to underdiagnosis.
Mechanism of Disease
Similar to allergic contact dermatitis, PACD is a delayed type IV hypersensitivity reaction; however, it only occurs when an exogenous chemical is applied topically to the skin with concomitant exposure to UV radiation, usually in the UVA range (315–400 nm). When exposed to UV radiation, it is thought that the exogenous chemical combines with a protein in the skin and transforms into a photoantigen. In the sensitization phase, the photoantigen is taken up by antigen-presenting cells in the epidermis and transported to local lymph nodes where antigen-specific T cells are generated. In the elicitation phase, the inflammatory reaction of PACD occurs upon subsequent exposure to the same chemical plus UV radiation. Development of PACD does not necessarily depend on the dose of the chemical or the amount of UV radiation. Why certain individuals may be more susceptible is unknown, though major histocompatibility complex haplotypes could be influential.
Clinical Manifestations
Photoallergic contact dermatitis primarily presents in sun-exposed areas of the skin (eg, face, neck, V area of the chest, dorsal upper extremities) with sparing of naturally photoprotected sites, such as the upper eyelids and nasolabial and retroauricular folds. Other than its c Department of Pediatrics, Division of Medical Genetics and Metabolism, and Center for Genomic Medicine, Massachusetts 02114, USA; Find articles by Lauren C Briere Department of Neurology, Division of Neurogenetics, Child Neurology, Massachusetts 02114, USA; Find articles by Melissa A Walker Department of Pediatrics, Division of Medical Genetics and Metabolism, Massachusetts 02114, USA; Find articles by Frances A High Department of Internal Medicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA; Find articles by Cynthia Cooper Department of Pediatrics, Division of Medical Genetics and Metabolism, and Center for Genomic Medicine, Massachusetts 02114, USA; Find articles by Cassandra A Rogers Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA; Find articles by Christine J Callahan Department of Biochemistry, Niigata University School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8510, Japan; Find articles by Ryosuke Ishimura Department of Biochemistry, Niigata University School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8510, Japan; Find articles by Yoshinobu Ichimura Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA; Find articles by Paul A Caruso Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA; Find articles by Nutan Sharma Division of Medical Genetics and Genomic Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37 This is a PDF-only article. The first page of the PDF of this article appears above. Subscribe and get access to all BMJ articles, and much more. Subscribe * For online subscription Access this article for 1 day for: You can download a PDF version for your personal record. .Lauren C Briere
Melissa A Walker
Frances A High
Cynthia Cooper
Cassandra A Rogers
Christine J Callahan
Ryosuke Ishimura
Yoshinobu Ichimura
Paul A Caruso
Nutan Sharma
Elly Brokamp
INDEX TO VOLUME 299 FOR 1989
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