solitary epithelioid histiocytoma
Reticulohistiocytoma and multicentric reticulohistiocytosis are designations for uncommon, incompletely characterized histiocytic proliferations of the skin or soft tissues. There is a uniform group of 44 lesions composed of epithelioid histiocytes, comprising a subset of lesions originally designated as reticulohistiocytoma, and the term "solitary epithelioid histiocytoma" (SEH) have been proposed.
SYnopsis
median age : 35 years (range, 2.5-74 years)
superficial, circumscribed, mildly elevated, solitary lesion (size range, 1.5-11 mm; median, 4 mm), located in the trunk wall (n = 16), lower extremity (n = 12), head and neck (n = 8, including 2 in the oral cavity), upper extremity (n = 6), penis (n = 1), and an unspecified site (n = 1).
upper and mid-dermis
large epithelioid histiocytes with a varying number of lymphocytes and neutrophils. The histiocytes had abundant, typically densely eosinophilic, cytoplasm and mostly mild, if any, nuclear atypia.
Multinucleated forms with randomly oriented nuclei
The histiocytes have low mitotic activity (range, 0-4 mitoses per 10 wide HPFs; median, 1 mitosis per 10 HPFs).
The lesions contain varying numbers of CD3-positive T cells, whereas B lymphocytes, plasma cells, eosinophils, and mast cells were scant, if present at all.
Immunohistochemistry
Epithelioid histiocytes were positive for CD163, CD68, lysozyme (variably), and vimentin.
They often had focal nuclear immunoreactivity for microphthalmia transcription factor, and they sometimes had focal reactivity for Factor XIIIa and S-100 protein.
Membrane positivity for CD31, CD43, and CD45 is variable.
The epithelioid histiocytes are consistently negative for CD3, CD20, CD30, HMB45, and keratins.
SEH is a benign, probably reactive, histiocytic proliferation of unknown etiology.
Differential diagnosis
Rosai-Dorfman disease
juvenile xanthogranuloma
granulomatous conditions
malignant neoplasms
- histiocytic sarcoma
- melanoma
- epithelioid sarcoma.
References
Miettinen M, Fetsch JF. Reticulohistiocytoma (solitary epithelioid histiocytoma): a clinicopathologic and immunohistochemical study of 44 cases.Am J Surg Pathol. 2006 Apr;30(4):521-8. PMID: #16625100#