22 April 2008 – Case of the Week #116
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Case of the Week #116
A 60 year old man had a pearly papular lesion of the scalp.
What is your diagnosis?
Epithelioid variant of benign fibrous histiocytoma
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 (AJSP 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 solitary epithelioid histiocytoma, Rosai-Dorman disease and granulomatous conditions. This case most closely resembles solitary epithelioid histiocytoma, a recently described lesion formerly called reticulohistiocytoma (AJSP 2006;30:521). It is composed of large epithelioid histiocytes, but 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. There is some overlap with epithelioid variant of benign fibrous histiocytoma regarding the staining pattern, as the histiocytes are immunoreactive for vimentin, and may have focal staining for Factor XIIIA. They are also immunoreactive for CD163, CD68 (may be focal), and negative for MelanA, S100 and keratin.
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, S100+, HMB45+), epithelioid sarcoma (deep seated, granuloma-type clusters with necrosis, more atypia, keratin+, CD163-), and histiocytic sarcoma (marked atypia and mitotic activity)
Epithelioid variant of benign fibrous histiocytoma has an excellent prognosis, with only rare recurrences reported after excision.
Nat Pernick, M.D., President
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