The appearance of dermatofibromas is markedly influenced by architectural, e.g. in deep penetrating dermatofibroma, and/or cellular/stromal criteria, e.g. in epithelioid cell histiocytoma or sclerosing dermatofibroma. Cellular neurothekeoma seems to be a variant of dermatofibromas with both architectural and cellular/stromal peculiarities, i.e. plexiform pattern, epithelioid cytology and stromal sclerosis.
An otherwise healthy 50-year-old woman presented with a 6-month history of having developed more than 100 generalized, non-confluent, reddish-brown, partially yellow-coloured papules. A non-epidemotropic, monomorphous infiltrate of vacuolated mononuclear, and occasionally multinuclear, histiocytes, positive for factor XIIIa and macrophage markers HAM56 and KiM1p, was consistent with the clinical impression of generalized eruptive histiocytomas. However, the additional reactivity for S100 protein, in the absence of features of histiocytosis X, suggested a diagnosis of indeterminate cell histiocytosis (ICH). Further immunohistochemical studies, performed on snap-frozen material, characterized the lesions as being diffusely positive with LN3 (HLA-DR), Leu4 (CD3) and Leu3 (CD4), the infiltrate in the upper dermis as reactive for OKT6 (CD1) and IOT6c (CD1c), and the infiltrate in the lower dermis as reactive for a variety of macrophage markers. Ultrastructural studies showed various non-specific features of histocytic disorders, but no Birbeck granules. Our findings confirm those of previous reports suggesting that ICH is a distinct histiocytic entity, characterized by immunophenotypic features of both X- and non-X histiocytoses. Generalized eruptive histiocytoma seems to be an early indeterminate stage of various non-X histiocytic syndromes including ICH, multicentric reticulohistiocytosis, xanthogranuloma and xanthoma disseminatum. The distribution pattern of the various X/non-X histiocytic markers suggests dermal arrest of antigen-presenting cells during their physiological trafficking from the skin to the lymph nodes.
An otherwise healthy 50-year-old woman presented with a 6-month history of having developed more than 100 generalized, non-confluent, reddish-brown, partially yellow-coloured papules. A non-epidemotropic, monomorphous infiltrate of vacuolated mononuclear, and occasionally multinuclear, histiocytes, positive for factor XIIIa and macrophage markers HAM56 and KiM1p, was consistent with the clinical impression of generalized eruptive histiocytomas. However, the additional reactivity for S100 protein, in the absence of features of histiocytosis X, suggested a diagnosis of indeterminate cell histiocytosis (ICH). Further immunohistochemical studies, performed on snap-frozen material, characterized the lesions as being diffusely positive with LN3 (HLA-DR), Leu4 (CD3) and Leu3 (CD4), the infiltrate in the upper dermis as reactive for OKT6 (CD1) and IOT6c (CD1c), and the infiltrate in the lower dermis as reactive for a variety of macrophage markers. Ultrastructural studies showed various non-specific features of histocytic disorders, but no Birbeck granules. Our findings confirm those of previous reports suggesting that ICH is a distinct histiocytic entity, characterized by immunophenotypic features of both X- and non-X histiocytoses. Generalized eruptive histiocytoma seems to be an early indeterminate stage of various non-X histiocytic syndromes including ICH, multicentric reticulohistiocytosis, xanthogranuloma and xanthoma disseminatum. The distribution pattern of the various X/non-X histiocytic markers suggests dermal arrest of antigen-presenting cells during their physiological trafficking from the skin to the lymph nodes.
We report five cases of plexiform fibrohistiocytic tumors, three classic subcutaneous lesions and two dermal ones. Both variants had similar profiles and were clinically indistinguishable. The lesions affected the trunk more than the upper extremities and were found in children and young adults (18.4 +/- 12.8 years). They showed a marked female predominance (4:1, including both dermal variants). Clinically, they were skin-colored, hard nodules of 1-2-cm diameter that resulted in such differential diagnoses as fibroma, histiocytoma, pilomatricoma, or cyst. Interestingly, one subcutaneous case with a painful "worms in the sack" presentation was thought to represent a plexiform neurofibroma. Histology revealed well-circumscribed dermal or subcutaneous plexiform lesions with a characteristic biphasic appearance. Most of the tumor bulk consisted of spindle-shaped to stellate myofibroblasts with a variable admixture of collagen or loosening of stroma. In the center of the plexiform strands and nodules, a few osteoclast-like giant cells as well as epithelioid mononuclear cells (< 10%) were found. Myofibroblasts were positive with HHF35 and for smooth muscle actin in three of five cases. Osteoclast-like giant cells were positive with KP1 in all five cases. Both types of cells stained with the macrophage marker Ki-M1p. A broad panel of other markers was negative. This series expands the spectrum of plexiform fibrohistiocytic tumor, but it also broadens the differential diagnosis of (dermal) plexiform lesions, which at present includes spindle cell nevi, schwannomas, neurofibromas, granular cell tumors, nerve sheath myxomas (neurothekeomas), spindle cell lipomas, and tufted angiomas.
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