Progressive Mucinous Histiocytosis

Progressive mucinous histiocytosis is a rare, benign, non‐Langerhans cell histiocytosis limited to the skin. A total of ten cases, all women, in four families, and one sporadic case have been described in the English literature. The disorder usually begins in childhood and progresses slowly. We report two sporadic cases of adult‐onset progressive mucinous histiocytosis in unrelated African American women, age 48 and 55 years old respectively, who developed red‐brown and flesh‐colored, asymptomatic papules on the face, arms and legs without truncal, mucosal or visceral involvement. The lesions show no spontaneous regression. Both patients lack associated systemic symptoms including polyuria, polydipsia or seizures. There is no underlying hyperlipidemia, paraproteinemia or lymphoproliferative disease. No family history of similar lesions can be identified. Light microscopy reveals dermal proliferation of spindle‐shaped histiocytes with abundant mucin deposition. Electron microscopy demonstrates a high number of myelin‐figures or zebra bodies in the cytoplasm of histiocytes. On immunohistochemistry, positive staining with macrophage markers CD68, HAM56 and lysozyme, and Factor XIIIa, a transglutaminase present in dermal dendrocytes, and negative staining with Langerhans cell markers CD1a and S100, and CD34, a marker present in dermal dendritic cells derived from uncommitted mesenchymal cells, are observed.