Rosai-Dorfman disease is a histiocytic disorder with a poorly-defined pathogenesis. Recent molecular studies have revealed recurrent mutations involving genes in the MAPK/ERK pathway in Langerhans cell histiocytosis and Erdheim-Chester disease. However, cases of Rosai-Dorfman disease have rarely been assessed. We performed next-generation sequencing to assess 134 genes on 21 cases of Rosai-Dorfman disease, including 13 women and 8 men with a median age of 43 years (range, 3–82). Thirteen had extranodal, 5 had nodal, and 3 had coexistent nodal and extranodal disease. The head and neck region was the most common area involved (n=7). Mutation analysis detected point mutations in 7 (33%) cases, including KRAS (n=4) and MAP2K1 (n=3). No mutations were identified in ARAF, BRAF, PIK3CA, or any other genes assessed. Immunohistochemistry demonstrated p-ERK overexpression in 3 cases, all harboring MAP2K1 mutations. Patients carrying mutated genes were younger (median age, 10 versus 53 years, p=0.0347) with more pediatric patients (4/7 versus 1/14, p=0.0251). The presence of mutations correlated with location being more common in the head and neck region; 6/7 (86%) mutated versus 1/14 (7%) unmutated cases (p=0.0009). All 5 (100%) mutated cases with available staging information had a multifocal presentation, whereas only 3/11 (27%) unmutated patients had multifocal disease (p=0.0256). Treatment information was available in 10 patients, including radical resection (n=4), resection and radiation (n=3), and cladribine-based chemotherapy (n=3). With a median follow-up of 84 months (range, 7–352), 7 remained in clinical remission and 3 had persistent disease. No correlation between mutation status and clinical outcome was noted. In summary, we detected mutually exclusive KRAS and MAP2K1 mutations in one third of cases of Rosai-Dorfman disease suggesting this subgroup are clonal and involve activation of MAPK/ERK pathway. Our data contributes to the understanding of the biology of Rosai-Dorfman disease and points to potential diagnostic and therapeutic targets.

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Dermatopathic lymphadenopathy (DL) is a distinctive type of lymph node hyperplasia that typically occurs in the setting of chronic dermatologic diseases. DL generally self-resolves following disappearance of the underlying skin stimulus and does not require any specific therapy. We recently observed multiple myeloma oncogene 1/interferon regulatory factor 4 (MUM1/IRF4) expression in a case of DL using immunohistochemical methods. The goal of this study was to systematically assess DL cases for MUM1/IRF4 expression and to survey other histiocytic and Langerhans cell lesions. We particularly focused on Langerhans cell histiocytosis (LCH) because the differential diagnosis of DL versus LCH in lymph nodes can be challenging. We identified high expression of MUM1/IRF4 in all 22 cases of DL tested. Specifically, MUM1/IRF4+ dendritic cells comprised 50% to 90% (median, 80%) of all dendritic cells in the paracortex of dermatopathic lymph nodes, always showing moderate or strong intensity. Among 10 DL cases stained for MUM1/IRF4 and langerin/CD207 using dual immunohistochemistry, MUM1/IRF4+ and langerin+ Langerhans cells represented 5% to 60% (median, 30%) of paracortical dendritic cells. MUM1/IRF4 was also positive in reactive Langerhans cells in skin biopsy specimens of all cases of spongiotic dermatitis (n=10) and normal skin (n=15), and was negative in all cases of LCH (n=24), Rosai-Dorfman disease (n=10), follicular dendritic cell sarcoma (n=5) and histiocytic sarcoma (n=4). In aggregate, our findings support the utility of MUM1/IRF4 to highlight the dendritic cells of DL and to distinguish DL from other histiocytic and Langerhans cells lesions.

Granular Parakeratosis is a rare disorder of keratinization usually presented in adults. There are only fews reports in children. We present two cases, one in an adult and the other in a 7-month-old infant.

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One of the pathogenic causes of cutaneous inflammatory pseudotumors is chronic localized fibrosing leukocytoclastic vasculitis (CLFLCV), a vasculitic reaction pattern seen in granuloma faciale (GF), a localized vasculitis, and erythema elevatum diutinum (EED), a generalized vasculitis. Patients with myelodysplastic syndromes (MDSs) are at risk for a diverse spectrum of cutaneous neutrophilic dermatoses such as EED. Herein, we report a 74-year-old man who presented with a large ulcerative, fungating tumor affecting the right flexor ankle caused by CLFLCV. During his workup and management, MDS and Philadelphia chromosome-negative chronic myeloid leukemia was diagnosed. Surgical excision of the inflammatory mass promptly triggered tumor recurrence, whereas antineutrophil therapy (dapsone coupled with hydroxyurea, and prednisone) lead to tumor regression. Histopathologic examination revealed an eosinophilic-rich small-vessel neutrophilic vasculitis associated with storiform and angiocentric fibrosis (GF-like). In the regions of fibrosis, dilated lymphatic and vascular spaces were numerous, some of which were congested with small CD3-positive lymphocytes (intralymphatic and intravascular lymphocytosis). These findings indicate coexisting localized lymphedema. By direct immunofluorescence, IgM and C4d vessel deposits were detected. The pathogenesis of the fibrotic nodules and plaques of CLFLCV is suspected to be due to recurring bouts of immune-complex vasculitis, creating a cycle of vessel damage followed by reparative granulation tissue. Poor lymphatic drainage may be the underlying factor initiating and maintaining recurrent, localized episodes of immune-complex vasculitis and progressive fibrosis. Although his tumor histopathology resembled GF-eosinophilic rich CLFLCV-the clinical context points to a solitary and paraneoplastic case of EED.