March 2010 – Case of the Month #8

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We thank Dr. Keloth E. Pradeep, Wrexham Maelor Hospital, United Kingdom, for contributing this case.  To contribute a Case of the Week, follow the guidelines on our Case of the Week page.

Dermatology Case of the Month #8

Clinical history

A 60 year old man had a pearly, papular lesion on his scalp.

Micro images:

Low power

High power

Immunostains:

Vimentin                     Factor XIIIA

CD68                           Keratin

Melan-A

What is your diagnosis? 

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Diagnosis:

Epithelioid variant of benign fibrous histiocytoma

Discussion

This uncommon variant of benign fibrous histiocytoma (dermatofibroma) usually presents as a small (1 cm or less), solitary, elevated nodule in the extremities.  The mean age is 42 years (Br J Dermatol 1989;120:185).  It is composed of uniform, medium to large, angulated epithelioid cells, often perivascular, with overlying epidermal effacement (Am J Surg Pathol 1994;18:583).  There is minimal inflammation, and no prominent giant cells.  The phenotype is predominantly myofibroblastic and not histiocytic.  These tumors are immunoreactive for Factor XIII, but negative for CD68 and CD163.  They may arise from the dermal microvascular unit (J Cutan Pathol 2003;30:415).  

The differential diagnosis includes reticulohistiocytoma, Rosai-Dorman disease and granulomatous conditions.  This case most closely resembles reticulohistiocytoma, also called solitary epithelioid histiocytoma (Am J Surg Pathol 2006;30:521).  It is composed of large epithelioid cells with the phenotype of histiocytes, and with abundant dense eosinophilic and glassy cytoplasm, often with spike-like cytoplasmic extensions.  The nuclei are round/oval with distinct nucleoli.  Unlike this case, there are variable nuclear grooves and multinucleated cells, and frequent lymphocytes and neutrophils.  The tumor cells are immunoreactive for CD163 and CD68, as well as vimentin.  There may be focal staining for Factor XIIIA.

Rosai-Dorfman disease usually presents with multiple skin lesions and adenopathy.  Its histiocytes are pleomorphic with emperipolesis and S100 staining.  There are also prominent B cells and plasma cells.  Granulomas also contain epithelioid histiocytes, but they are in well-formed clusters and are surrounded by lymphocytes. 

Malignant lesions to consider include melanoma (tight clustering of cells, marked atypia, S100+, HMB45+), epithelioid sarcoma (deep seated, granuloma-type clusters with necrosis, definite atypia, keratin+, CD163-), and histiocytic sarcoma (marked atypia and mitotic activity).

The epithelioid variant of benign fibrous histiocytoma has an excellent prognosis, with only rare recurrences reported after excision.

Nat Pernick, M.D., President

and Kara Hamilton, M.S., Associate Medical Editor
DermatologyOutlines.com
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Bingham Farms, Michigan (USA) 48025

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Email: NatPernick@hotmail.com