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Abstract

An accumulation of clonally restricted, terminally differentiated, monocyte-derived dendritic cells within the skin is a unique cutaneous manifestation of chronic myeloproliferative disease that falls under the designation of monocytic papulosis. We present a 76-year-old man with a history of chronic myelomonocytic leukemia (CMML) who developed intensely pruritic erythematous papules coalescing into plaques on the chest, back, and forearms, recalcitrant to antihistamines and topical steroids. A skin biopsy showed a striking nonepidermotropic superficial and deep micronodular infiltrate of well-differentiated mature atypical histiocytes accentuated around blood vessels, the adventitial dermis of the eccrine coil, and hair follicles. The monocytic ontogeny was suggested by the eccentrically disposed round, oval, and reniform nuclei and relatively abundant lightly eosinophilic cytoplasm. The cells were highlighted by CD4, CD11c, CD31, and HLA-DR; CD14 marked a subset of histiocytes, with a minor component expressing myeloperoxidase, and some cells staining for MxA. The Ki-67 proliferation index was mildly increased (~5%). The findings were compatible with a neoplastic infiltrate of mature monocytes. The diagnosis was rendered of monocytic papulosis, a unique monocytic proliferative disorder characterized by an accumulation of mature neoplastic histiocytic elements in the skin seen in patients with chronic myeloproliferative disorders. We originally coined the term myeloid dendritic cell dyscrasia as the monocytes showed a phenotypic profile characteristic for the myeloid dendritic cell. Like lymphomatoid papulosis, the lesions can spontaneously regress, and there is no correlation with an aggressive clinical disease.