A sporadic case of progressive mucinous histiocytosis.

Hereditary progressive mucinous histiocytosis is a rare autosomal dominant non-Langerhans cell histiocytosis. We describe a sporadic case of this syndrome in a 64-year-old woman who had multiple dark-red dome-shaped papulonodules located mainly on the back of her hands, forearms and thighs. Light microscopy revealed a circumscribed upper dermal aggregate of ovoid or spindle-shaped histiocytes with abundant mucin deposition. Iron deposits and numerous mast cells were scattered throughout the tumour but giant cells were rare. Electron microscopy revealed a high number of zebra bodies and myeloid bodies in the cytoplasm of the histiocytes. Immunohistochemistry showed positive labelling with alpha-1 antitrypsin, Factor XIIIa and CD68, while CD1a, CD34 and S100 protein were negative. The differential diagnosis of histiocytic syndromes is discussed.