Abstract

Sweet syndrome (SS), or acute febrile neutrophilic dermatosis, is characterized by tender, edematous plaques accompanied by fever and leukocytosis. Histologically, SS typically shows mature neutrophilic infiltrates in the dermis, karyorrhexis, papillary dermal edema, and sometimes focal leukocytoclastic vasculitis (LCV). Histology can vary, and a lobular neutrophilic panniculitis can sometimes be present, complicating the diagnosis. Histologic findings in SS can also differ based on the chronicity of the biopsied lesion and the presence of associated myeloproliferative disorder.

In the early stages of SS, immature neutrophils are often observed, while in later stages, Miescher radial granulomas— small histiocytes arranged radially around a central cleft—can aid in diagnosis even when most of the neutrophilic infiltrate is replaced by chronic inflammation. This finding permits distinction of late or resolving SS from reactive granulomatous dermatitis (which includes palisaded), granuloma annulare, and histiocytoid SS. Additionally, elastophagocytosis can be a useful diagnostic clue in late SS.

We describe three cases of late SS with Miescher radial granulomas. All patients exhibited the classic clinical features of SS. One early biopsy showed significant dermal edema and neutrophils, while late lesions displayed Miescher radial granulomas at the junction of the dermis and subcutis along with a mixed dermal inflammatory infiltrate with neutrophils as a minor component. These cases emphasize the diagnostic value of Miescher radial granulomas in identifying the histopathologic evolution of late or resolving SS.  While historically described in association with SS, erythema nodosum, and erythema induratum, this useful clue has only rarely been described in the literature.