Older Male with a Skin Lesion

Matthew R. Muenster, M.D.

Specimen Type:



63 year-old man with a 6-month history of a 6 millimeter, bright red, elevated, dome-shaped papule of the left upper arm. Clinical diagnosis: Molluscum contagiosum vs adnexal tumor; rule out non-melanoma skin cancer.

Pathologic Features:

There is a nodular collection of inflammatory cells forming a dome-shaped papule with a collarette of epithelium surrounding it. The collection is well-circumscribed, and at higher power, is composed predominantly of large cells containing abundant amphophilic cytoplasm that displaces the nucleus to one side. Also, numerous admixed neutrophils, eosinophils, and lymphocytes are present.

Differential Diagnosis:

  • Squamous Cell Carcinoma
  • Metastatic Melanoma
  • Reticulohistiocytoma
  • Molluscum contagiosum infection



Reticulohistiocytoma is an uncommon, poorly understood proliferation of histiocytes containing characteristic abundant “glassy,” eosinophilic cytoplasm. When lesions are multiple and systemic, the disorder has been termed multicentric reticulohistiocytosis. Lesions are described in both men and women, most commonly occurring on the trunk and lower extremity. Usually, the lesion is solitary as in this case and does not recur. Reticulohistiocytoma typically stains positive for CD68, CD163, and vimentin. In our case, and in a subset of reported cases, S100 stains positively as well, though most do not. Immunostains for MART-1, and AE1/AE3 were negative.


  1. Miettinen, M, Fetsch, JF. Reticulohistiocytoma Am J Surg Pathol, Vol 30, Num 4, April 2006.
  2. Weedon, D. Skin Pathology, second edition. Churchill Livingston, 2002. p. 1072.