Photosensitive erythema multiforme and erythema multiforme-like polymorphous light eruption.
Photosensitive erythema multiforme (EM) is a rare disorder. It usually occurs only if a herpes virus infection or ingestion of drugs precedes exposure to sunlight in selected patients. We report a 37-year-old man who had recurrent EM eruptions following sun exposures over a period of 20 years. Lesions were prevalently located on exposed skin, but unexposed skin and mucosa of the oropharynx were also affected. The patient had poor tolerance to sunlight and denied having herpes simplex infection or using drugs. Provocative phototest induced clinically and histologically similar lesions at low dose thresholds of UVA (10 J/cm2) and UVB (100 mJ/cm2). On the basis of clinical and histological findings and results of phototesting, a diagnosis of photosensitive EM was made. The EM-like variant of polymorphous light eruption is discussed in the differential diagnosis.