Case for diagnosis
A 1-month-old boy, born at term after an uneventful pregnancy, with a birth weight of\n3,480g. First child of healthy and unrelated parents. At birth his mother noticed a 1 x\n1.5 cm erythematous, infiltrated, perianal plaque that rapidly progressed to ulceration\n(). The patient was otherwise healthy.\nA second evaluation at age two and a half months showed a complete and spontaneous\nresolution of the lesion (). Serologic\ntest for syphilis (VDRL) was negative both for the mother and the patient.\nHistopathological exam revealed a dermal infiltrate with predominance of large, round\nhistiocytic cells with dense eosinophilic cytoplasm, with ground glass appearance, and\neccentric reniform nuclei ().\nImmunohistochemical staining was positive for S100 and CD1a ( and ). Routine\nlaboratory workup and radiographs of chest, skull, pelvis and long bones were within\nnormal ranges. The patient remains asymptomatic with no signs of recurrence.