Introduction: 5-Fluorouracil is a fluoropyrimidine antineoplastic medication that is used to topically treat actinic keratoses. Although local adverse effects to the drug are common and anticipated, distant skin reactions are rare and unexpected. In this case report, we describe a patient who developed seborrheic dermatitis-like eruption at a distant site after topical application of 5-fluorouracil to his arms.

Case report: A 63-year-old man with actinic keratoses on his arms developed a facial seborrheic dermatitis-like reaction after topically applying 5-fluorouracil 5% cream twice daily to actinic keratoses on his forearms for 7 days. The facial dermatosis resolved shortly after discontinuation of the 5-fluorouracil; upon rechallenge of topical 5-fluorouracil on his arms, the facial seborrheic dermatitis recurred.

Discussion: Several case reports have been published which describe exacerbations of preexisting seborrheic dermatitis with local topical 5-fluorouracil. Additionally, one case series describes the development of scrotal dermatitis in two patients after distant treatment with 5-fluorouracil. The pathogenesis that causes this distant reaction is unclear.

Conclusion: We describe a patient with a seborrheic dermatitis eruption after topical application of 5-fluorouracil at a distant site. The etiologic association between the drug and adverse effect was confirmed with multiple cycles of application and discontinuation of the offending agent.