Histological Features of Flagellate Erythema

Flagellate erythema is a distinctive eruption characterized by "whip-like" linear or curvilinear streaks and plaques, occurring mainly on the trunk. It has classically been described in 2 disparate clinical settings: chemotherapy with bleomycin and ingestion of mushrooms (most commonly Shiitake mushrooms). Most of the literature comprises single case reports, often with minimal histological description of rather nonspecific features. We describe in detail the histological features of 3 cases of flagellate erythema (2 related to bleomycin therapy and one related to ingestion of mushrooms) and review the findings described in the literature to define the spectrum of histological changes encountered in this eruption. Our 3 cases showed mild epidermal changes, with spongiosis and variable interface inflammation. All 3 showed a relatively prominent dermal lymphohistiocytic infiltrate, with features suggestive of a lymphocytic vasculopathy extending to at least the mid-reticular dermis. Eosinophils were a prominent component of the inflammatory infiltrate in 2 cases. Our review of the literature identified a total of 45 publications, representing reports of 46 patients, containing histological information. As well as bleomycin- and mushroom-related cases, similar eruptions have been reported in the context of connective tissue disease and other drugs. Although cases related to connective tissue disease show features of the underlying condition, cases secondary to drugs or mushrooms predominantly show features compatible with common patterns of exanthematous/morbilliform drug reaction. In particular, subtle spongiosis and/or interface dermatitis combined with a dermal lymphocytic infiltrate that includes increased numbers of eosinophils is a common finding. Features of a lymphocytic vasculopathy may be seen in a subset of these cases.