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Multicentric reticulohistiocytosis is a rare non-Langerhans cell histiocytosis of unknown etiology. It is classified as multicentric because of multisystem involvement. The disease predominantly affects the skin and joints, but visceral involvement is possible. Multiple erythematous-brownish, pruritic nodules and papules on the face, hands, neck, and trunk are characteristic. It is associated with autoimmune diseases, or malignant neoplasms are seen in 20% to 30% of patients with multicentric reticulohistiocytosis. The diagnosis is based on histopathology of affected tissues. As it is an underreported disease, there is no standardized treatment. A case of multicentric reticulohistiocytosis is reported as a paraneoplastic manifestation of ductal breast cancer, being successfully treated with no recurrence after two years of follow-up. Few cases of multicentric reticulohistiocytosis associated with breast cancer have been reported in the literature., Competing Interests: The authors declare that there are no conflicts of interest in this manuscript., (This work is licensed under a Creative Commons Attribution 4.0 International License.)

Objective: To investigate the clinical features of multicentric reticulohistiocytosis (MRH)., Methods: The clinical manifestations, laboratory examination results and histologic characteristics of eleven patients with MRH were collected and compared with those of 33 patients with rheumatoid arthritis., Results: In total, 72.7% of the MRH patients were women. The median age was 46 years (range 33-84 years). Diagnosed by specific pathologic features, all MRH patients exhibited cutaneous involvement. The dorsa of the hands, arms, face and auricle were the most commonly affected areas. Nodules were also located on the legs, scalp, trunk, neck, and even the hypoglossis and buccal mucosa. Ten MRH patients (90.9%) had symmetric polyarthritis. Compared with rheumatoid arthritis (RA) patients, MRH patients were more likely to have distal interphalangeal joint (DIP) involvement (63.6% vs 24.2%, P = 0.017) and less likely to have elbow (36.4% vs 72.7%, P = 0.003), ankle (45.5% vs 93.9%, P < 0.001) and metacarpophalangeal joint (MCP) (36.4% vs 78.8%, P = 0.009) involvement. Positivity for rheumatoid factor (RF) (36.4% vs 84.6%, P = 0.001) and anti-CCP antibody (9.1% vs 81.8%, P = 0.000), as well as the median RF titer [43.8 (31.7-61.0) vs 175.4 (21.3-940.3), P = 0.021], in MRH patients was lower than in RA patients. Elevation of the erythrocyte sedimentation rate (ESR) was also less common in MRH patients than in RA patients (36.4% vs 72.7%, P = 0.030). After treatment with median- to large-dose corticosteroids and disease-modifying antirheumatic drugs, 8 patients achieved complete remission and 2 patients partial remission (skin lesions ameliorated, joint lesions not ameliorated)., Conclusion: Always pathologically diagnosed, MRH is a systemic disease involving RA-like erosive polyarthritis and a specific distribution of skin nodules characterized by "coral beads". More DIP involvement and less elbow, ankle and MCP involvement are seen in MRH than in RA. In addition, less positivity and lower-titer RF, uncommon presence of anti-CCP antibodies and ESR elevation may be helpful to distinguish MRH from RA., (© 2022. The Author(s).)

Abstract: Xanthoma disseminatum (XD) is a rare non-Langerhans cell histiocytosis characterized by xanthomatous lesions in the absence of hyperlipidemia. XD usually develops in young adults, and there are rare cases among children. BRAF mutations are frequent in Langerhans cell histiocytosis and Erdheim-Chester disease but absent or only rarely detected in other histiocytosis. Herein, we described a 6-year-old Chinese girl presented with generalized skin lesions and diabetes insipidus for 5 months. There were multiple periorbital xanthelasma with histopathological features of foamy histiocytes infiltration with Touton cells. Pituitary magnetic resonance imaging showed pituitary enlargement and pituitary stalk thickening. The presence of BRAF p.V600E mutation makes this case distinctive and also offers a potential therapeutic target. According to our review of the literature, this is the first pediatric XD with diabetes insipidus and BRAF mutation., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Abstract: Multicentric reticulohistiocytosis (MRH) is a rare multisystem disorder, primarily affecting the skin and joints. As severe joint damage is a possible symptom, early diagnosis and therapeutic intervention are required. Cutaneous lesions present with characteristic features such as discrete reddish nodules, especially on acral locations. Additionally, the face, scalp, trunk and extremities are also affected. Xanthomatous plaques are also seen on the face. The cutaneous manifestations of MRH are various, which therefore should be differentiated from several diseases. In particular, MRH has been reported to assume clinical appearances resembling Gottron papules, periungual erythema, V-neck erythema, shawl sign, and poikiloderma associated with dermatomyositis. Histopathologic features show proliferation of multinucleated giant cells with abundant eosinophilic granular ground glass-like cytoplasm in the dermis. Multicentric reticulohistiocytosis is occasionally paraneoplastic and is associated with internal malignancies. The appropriate therapies are still challenging, and oral prednisolone, immunosuppressants, and recent biologics are used. In this article, cutaneous lesions, histopathology, and pathogenesis of MRH are mainly discussed from a dermatological perspective. It is important, not only for dermatologists but also for rheumatologists and orthopedists, to be able to distinguish between the various types of skin lesions brought on by MRH. Cutaneous signs are important diagnostic clues and assessment tools for therapeutic efficacy., Competing Interests: The author declares no conflict of interest., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Multicentric reticulohistiocytosis (MRH) is a rare type of non-Langerhans cell histiocytosis characterized by coral-toned papules with predilection for dorsal surfaces in addition to severe arthropathy. It sometimes proves difficult to differentiate these joint and skin findings clinically from certain rheumatologic diseases, primarily dermatomyositis. Herein, we present an 82-year-old woman who presented with the clinical findings described above and was subsequently diagnosed with MRH after biopsy and review of relevant clinical history. Because about 25% of patients diagnosed with MRH have an underlying occult malignancy, our patient underwent a complete malignancy workup that was negative. She was treated with systemic corticosteroids and methotrexate, which resulted in an improvement of the arthritis and constitutional symptoms. This case demonstrates that in patients with both rheumatologic and dermatologic symptoms, particularly on acral surfaces, MRH must be a diagnostic consideration. Identifying this disease early in its course can prevent negative consequences for the patients, specifically arthritis mutilans and upper airway involvement.

Reticulohistiocytoses (RH) are rare and clinically heterogeneous histiocytic disorders of dermatological interest. Three clinical entities with superimposable histopathological features are currently considered, namely solitary reticulohistiocytoma, diffuse/generalized reticulohistiocytosis and multicentric reticulohistiocytosis. Although in the last decade, RH studies have only minimally progressed, histiocytosis research has advanced considerably: the prognostic and therapeutic importance of the clinical subclassification of histiocytosis patients as well as of the detection of genetic alterations in the genes of the ERK pathway has been highlighted. According to these insights, we previously reported the presence of molecular alteration RH and described a subset of patients with disseminated multisystem involvement lacking arthritis. In the present review, we aim to update and revise the knowledge regarding RH. We first reviewed their histopathological, immunophenotypical and ultrastructural features, discussed their histopathological differential diagnosis with other conditions characterized by infiltrates made of oncocytic or epithelioid cells (with special regard to Destombes-Rosai-Dorfman disease) and finally summarized the molecular landscape of RH. We therefore tried to adjust the clinical subclassification of Langerhans cell histiocytosis to the clinical phenotypes of RH, outlining five clinically different groups of patients. Finally, we reconsidered the clinical workflow to the evaluation of RH patients, in light of the 5 different clinical groups and discussed the different therapeutic approaches and the possible role of target inhibitors., (© 2020 European Academy of Dermatology and Venereology.)

Objectives: Multicentric reticulohistiocytosis (MRH), a rare histiocytic disease that can mimic other rheumatic conditions, may be associated with cancer and other autoimmune disorders. To better understand the disorder and its other associations, we aimed to evaluate clinical correlates and outcomes of all patients with MRH seen at Mayo Clinic, Rochester between 1980 and 2017., Methods: A retrospective medical record review was conducted to identify all patients with MRH between 1 January 1980 and 30 April 2017., Results: We identified 24 patients with biopsy-proven MRH (58% female, 75% Caucasian, median age at diagnosis 52 years, median follow-up of 2.3 years). All patients had cutaneous and articular involvement; 23 (96%) patients had papulonodular skin lesions (87% periungual and dorsal hand) and seven (30%) mucosal nodules; and 22 (92%) patients had arthralgias, 21 (88%) joint effusions and 13 (54%) synovitis. Most frequently used therapies included corticosteroids, cyclophosphamide, methotrexate and bisphosphonates. Biologics were used in four patients. Nine patients had symptomatic resolution at 1 year and 12 partial improvement. Radiological findings included erosive changes in three (60%) patients and arthritis mutilans in two patients (40%). Twenty-nine per cent of patients had a concomitant autoimmune disease and 25% malignancy including melanoma, endometrial, peritoneal and lung carcinoma. The 5-year survival rate was 85% (95% CI: 74, 100%)., Conclusion: To our knowledge, this is the largest single-centre series of patients with MRH highlighting the rarity of the condition and an unmet need for treatment options that can allow sustained disease remission. It also highlights the need for a high vigilance for malignancy and autoimmune diseases., (© The Author(s) 2019. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Competing Interests: Competing interests: None declared.

Langerhans cell histiocytosis (LCH) is a rare histiocytic disorder resulting from dysregulated clonal proliferation of Langerhans cells. Reticulohistiocytosis (RH) is another rare histiocytosis caused by the proliferation of histiocytes other than Langerhans cells. Co-existence of LCH and RH in different organs and in the same skin area has not been reported. We present the case of a 20-year-old woman who initially had co-existing bone LCH and cutaneous RH. After 1 year of chemotherapy with cytarabine, bone LCH significantly improved but cutaneous LCH developed in the same area where cutaneous RH was, resulting in hybrid LCH and RH of the skin. This unique history provides some evidence to support the theory that LCH and RH originate from the same stem cells and subsequently develop into hybrid LCH and RH of the skin in a cytokine environment influenced by chemotherapy. Repeat skin biopsies may be considered for adjusting treatment regimens in LCH patients whenever pre-existing skin lesions progress., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Competing Interests: Competing interests: None declared.