Primary papular xanthoma of children: a clinicopathologic, immunohistopathologic and ultrastructural study.

Papular xanthoma (PX) is a very rare skin disorder. We describe a typical case of PX in a 13-month-old Chinese boy who presented with numerous yellow-red papulonodules, 2-8 mm in diameter, mainly on the face, both upper extremities, and abdomen of 10 months duration. Histologic studies showed a diffuse monomorphous infiltrate of foamy cells in the upper dermis. The foamy cells stained positively with oil red O and CD68. The periodic acid Schiff (PAS) stain, S-100 protein, CD1a, CD56, lysozyme, alpha1-antitrypsin, and factor XIIIa were all negative in the foamy cells. The electron microscopic (EM) studies revealed the morphologic features of macrophages with electron-dense, membrane-limited lipid vacuoles in the cytoplasm. After 14 months, neither spontaneous regression nor anetoderma-like scars were noted. Our immunohistochemical and ultrastructural studies support the notion that the origin of the foamy cells is the macrophage rather than the factor XIIIa (+) dermal dendrocyte. There was no associated or underlying disease in this case. We suggest the term primary PX for cases such as this one.