Solitary and generalized variants of spindle cell xanthogranuloma (progressive nodular histiocytosis).

Twelve cases of solitary spindle cell xanthogranuloma, seven of which had originally been misdiagnosed as dermatofibroma/benign fibrous histiocytoma, were clinicopathologically compared with four cases of progressive nodular histiocytosis, a rare generalized non-X histiocytic disorder. Clinically, a single brown-yellowish papule or nodule is characteristic of solitary spindle cell xanthogranuloma, multiple generalized lesions of progressive nodular histiocytosis. Solitary spindle cell xanthogranuloma occurs with decreasing frequency on the head, neck, upper trunk, or occasionally the extremities of young adults (aged 20-40 years), progressive nodular histiocytosis mostly on the trunk of older patients (aged 40-60 years), both without sex predilection. Histologically, both entities are characterized by predominance (> 90%) of spindle-shaped histiocytes arranged in a storiform pattern. Other mononuclear (vacuolated, xanthomatized, scalloped, oncocytic) and multinucleate (Touton) histiocytes are also regularly seen. Immunohistochemically, both entities exhibit a macrophage/dendritic cell lineage positive for KP1/Ki-M1p (CD68), HAM 56 and factor XIIIa as well as for smooth muscle specific actin and HHF35. Ultrastructurally, dense, regularly laminated, myeloid or pleomorphic cytoplasmic inclusions may be found, but no Birbeck granules are present. This study documents that both solitary spindle cell xanthogranuloma and progressive nodular histiocytosis are distinct entities within the spectrum of a xanthogranulomatous reaction characterized by predominance of spindle-shaped histiocytes.