Hereditary progressive mucinous histiocytosis

We describe a 61‐year‐old woman who presented with multiple small, firm, shiny, skin‐coloured papules in a symmetrical pattern on the dorsum of the hands, sides of the fingers and extensor aspect of the forearms. These had slowly increased in number over a period of 40 years, and were asymptomatic. Both laboratory results and systemic review were unremarkable. Histological examination of six papules revealed well‐circumscribed but unencapsulated dermal nodules composed of epithelioid histiocytes and abundant alcian blue‐positive mucin separating broad bundles of collagen. Histiocytes within the nodule stained positively with vimentin, and were focally positive for α 1 ‐antitrypsin and lysozyme. The interstitium was positive for tenascin. On electron microscopy, the histiocytes showed numerous circular, osmophilic myelin bodies and zebra bodies reminiscent of those seen in lysosomal storage diseases. Our patient’s clinical, histological and ultrastructural features have been previously described as hereditary progressive mucinous histiocytosis, a rare familial form of eruptive histiocytoma characterized by multiple persistent papules with prominent mucinosis.