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The clinical utility of 18 F-FDG PET/CT is being increasingly recognized in histiocytic disorders. We report the case of a 23-y-old woman who presented with slowly progressive, yellowish-brown papules, plaques, and nodules over her face and flexures. Besides the multiple cutaneous lesions, lesions of the brain, stomach, gallbladder, and marrow were additionally revealed by baseline 18 F-FDG PET/CT. Skin biopsy and the overall clinical picture were consistent with xanthoma disseminatum. Subsequent PET/CT after cladribine therapy revealed a decrease in the extent and metabolic activity of most lesions, suggestive of a favorable response. This case report highlights the potential role of 18 F-FDG PET/CT in the accurate assessment of disease extent and posttreatment response in rare histiocytic disorders., (© 2023 by the Society of Nuclear Medicine and Molecular Imaging.)

Background: Xanthoma disseminatum (XD) is a rare form of non-Langerhans histiocytosis with extensive cutaneous involvement. There is a paucity of evidence-based recommendations for treatment decision-making. Previous case reports have established purine analogues, especially cladribine, as a hopeful first-line treatment option, but characterization of the clinical and pathological responses is lacking., Objectives: To characterize the clinical and pathological responses to cladribine monotherapy based on serial examinations in XD patients., Materials & Methods: We retrospectively studied the clinical, pathological and laboratory data in a cohort of five XD patients who received intravenous cladribine monotherapy with serial examinations in our hospital. Compared with baseline characteristics, changes in clinical features and pathological patterns were identified and analysed. We also conducted a literature review of reported cases of cladribine treatment in XD patients., Results: Four male and one female patient were involved in the study. All patients demonstrated satisfactory clinical responses to cladribine monotherapy after 5 to 10 cycles. We observed a pathological shift in pattern from classic xanthogranuloma to transitional fibrohistiocytic infiltration during the treatment, and pathological responses heralded persistent clinical improvement. Other than afebrile neutropenia, no prominent adverse events were identified. Sustainable lesion clearance was achieved in all five patients during the follow-up period, ranging from 19 to 66 months., Conclusion: Cladribine monotherapy is an effective and well-tolerated therapeutic option for XD patients. Pathological transformation is a signature of the clinical response and possibly unveils the underlying histiocyte biology of diseases in the xanthogranuloma family.

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.)

Background: Non-Langerhans cell histiocytosis (non-LCH) is a collective term that encompasses a long list of rare "histiocytosis" that do not meet the criteria for Langerhans cell histiocytosis (LCH). Among cutaneous non-LCH, the xanthogranuloma (XG) family represents a distinct group of disorders derived from dermal dendritic cells (DDCs) at different stages of differentiation., Objectives: To investigate the clinicopathological characteristics of the XG family in adults and review the relevant literature., Materials and Methods: We performed a retrospective clinicopathological study of five adult cases with a previous diagnosis of non-LCH. Clinicopathological features, immunophenotypes, genetic alterations and ultrastructural characteristics were analysed., Results: Skin biopsies revealed that all five cases were characterized by diffuse infiltration of polymorphic cells, which were immunoreactive to factor XIIIa but negative for Langerin, CD1a, and S100. None of the cases harboured the BRAF V600E mutation. Electron microscopy of two cases exhibited abundant cytoplasmic processes with numerous lysosome-like dense bodies and electron-lucent vesicles in the cytoplasm and extracellular matrix. The overall features suggested that DDCs are the cellular origin, and these cases fulfilled the criteria for the XG family., Conclusion: The XG family represents a spectrum of rare diseases with different clinical presentations, a wide range of morphological appearances, and a shared common origin (DDCs). This group of disorders has been proposed as a unique entity with diagnostic challenges that should not be underestimated.

A 9-year-old boy presented with multiple hyperpigmented papules over flexors with polyuria, polydipsia and progressive loss of vision. Histopathology of papule suggested a diagnosis of non-Langerhans cell histiocytosis and systemic evaluation showed central diabetes insipidus and optic atrophy. With a diagnosis of xanthoma disseminatum with significant neurological involvement, he received cladribine therapy and showed significant improvement in both cutaneous and nervous system lesions., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2019. No commercial re-use. See rights and permissions. Published by BMJ.)

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.)

Introduction: Multicentric reticulohistiocytosis (MRH) is a rare histiocytic disorder that involves the skin, joints, and visceral organs., Case Presentation: We report a 67-year-old woman with MRH who presented with a 2-years history of polyarthralgia and skin nodules. Her symptoms were an inflammatory polyarthropathy with punched-out lesions of the distal interphalangeal (DIP) joints of both hands. Doppler ultrasonography of the hands showed large bone erosions with power Doppler signals in the DIP joints. F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) demonstrated increased FDG uptake in cutaneous papules surrounding the affected joints, suggesting an inflammatory process. There was no evidence of malignancy. Biopsy samples of skin nodules exhibited dermal infiltration with CD68-positive histiocytes and multinucleated giant cells. The patient was diagnosed with MRH and treated with combination therapy comprising a steroid (prednisolone), tacrolimus, methotrexate, and infliximab, which resulted in clinical improvement. Following infliximab treatment, there was a significant decrease in a bone resorption marker (tartrate-resistant acid phosphatase 5b: TRACP-5b), suggesting that tumor necrosis factor-α targeting therapy may inhibit osteoclast formation and resorption activity in patients with MRH., Conclusion: MRH is a progressive destructive arthritic condition, and early diagnostic and therapeutic strategies are necessary to improve the outcome. FDG-PET/CT and joint ultrasonography might be noninvasive imaging modalities that could help diagnose MRH.

Multicentric reticulohistiocytosis (MRH) is a rare histiocytic proliferative disorder of uncertain etiology, characterized by mucocutaneous papulonodular lesions and progressive, symmetric erosive arthritis. MRH can coexist with various autoimmune disorders, tuberculosis, and malignancy. It usually occurs in the elderly and is very rare in children. This is probably the first case in which disease manifestation appeared in infancy in the form of skin lesions. The patient had recurrent ulceration of cutaneous lesions, which is unusual in MRH. Early diagnosis and aggressive treatment are essential to prevent progressive irreversible course and development of arthritis mutilans. Various drugs, such as steroids, nonsteroidal anti-inflammatory drugs, immunosuppressants, interleukin inhibitors, and tumor necrosis factor-α antagonist, have been tried with variable responses. The present case responded well to vinblastine and steroid, which have not been reported previously. Here, we document a case of MRH with early onset in infancy along with role of vinblastine and prednisone in its treatment., (Copyright © 2016 by the American Academy of Pediatrics.)

Unlabelled: Histiocytic neoplasms are clonal, hematopoietic disorders characterized by an accumulation of abnormal, monocyte-derived dendritic cells or macrophages in Langerhans cell histiocytosis (LCH) and non-Langerhans cell histiocytosis (non-LCH), respectively. The discovery of BRAF(V600E) mutations in approximately 50% of these patients provided the first molecular therapeutic target in histiocytosis. However, recurrent driving mutations in the majority of patients with BRAF(V600E)-wild-type non-LCH are unknown, and recurrent cooperating mutations in non-MAP kinase pathways are undefined for the histiocytic neoplasms. Through combined whole-exome and transcriptome sequencing, we identified recurrent kinase fusions involving BRAF, ALK, and NTRK1, as well as recurrent, activating MAP2K1 and ARAF mutations in patients with BRAF(V600E)-wild-type non-LCH. In addition to MAP kinase pathway lesions, recurrently altered genes involving diverse cellular pathways were identified. Treatment of patients with MAP2K1- and ARAF-mutated non-LCH using MEK and RAF inhibitors, respectively, resulted in clinical efficacy, demonstrating the importance of detecting and targeting diverse kinase alterations in these disorders., Significance: We provide the first description of kinase fusions in systemic histiocytic neoplasms and activating ARAF and MAP2K1 mutations in non-Langerhans histiocytic neoplasms. Refractory patients with MAP2K1- and ARAF-mutant histiocytoses had clinical responses to MEK inhibition and sorafenib, respectively, highlighting the importance of comprehensive genomic analysis of these disorders., (©2015 American Association for Cancer Research.)

A young male presented with panhypopituitarism (including diabetes insipidus) and temporal lobe epilepsy. A histology specimen of cutaneous papules was diagnostic of non-Langerhans histiocytosis. The diagnosis of xanthoma granulomata was considered based on the clinical and brain MRI findings. Brain lesions significantly worsened over time despite radiotherapy until anakinra induced a complete clinical and radiological remission of all active lesions. Although a single case, the outcome of this patient with xanthoma disseminatum treated with an interleukin-1 receptor antagonist opens and strengthens new and recent physiopathogenic and treatment perspectives for the otherwise difficult-to-treat non-Langerhans cell histiocytosis. Similar results with anakinra have been observed in patients with Erdheim-Chester disease and in multicentric reticulohistiocytosis., (© 2016 S. Karger AG, Basel.)

Importance: Generalized eruptive histiocytosis (GEH) is a rare non-Langerhans cell histiocytosis with a benign, self-healing course. Neoplastic hematologic disorders of the myeloid lineage have been reported in association with GEH in 4 patients. A clonal association between GEH and the underlying leukemia was suspected in these patients but could only be confirmed in one patient., Observations: A male patient in his 20s presented with asymptomatic red to brown macules and papules. A skin biopsy confirmed a diagnosis of GEH. His blood cell count revealed hypereosinophilia. Morphologic and molecular analyses from bone marrow and blood samples revealed FIP1L1-PDGFRA-positive chronic eosinophilic leukemia. The patient was treated with imatinib and achieved complete clinical remission of his leukemia and the GEH., Conclusions and Relevance: To our knowledge, this is the first report of a patient with GEH associated with FIP1L1-PDGFRA-positive chronic eosinophilic leukemia. Generalized eruptive histiocytosis in association with a myeloid neoplasm may occur in 2 variants: a reactive condition or a clonal derivative of the underlying leukemia. In this case, both diseases responded well after initiation of treatment with imatinib.

Multicentric reticulohistyocytosis (MRH) is a rare multisystemic non-Langerhans histiocytosis characterized by cutaneous nodules and severe destructive polyarthritis, sometimes associated with constitutional symptoms and various organ involvements. Its treatment remains empirical and challenging. We first report herein, the successful treatment of a multicentric reticulohistiocytosis patient with anakinra based on cutaneous biopsy immunostaining and serum cytokines features. A first-line treatment associating methotrexate, cortisone and hydoxychloroquine showed none improvement. Therefore, while further tests were performed to rule out an associated malignancy, auto-immune disease or mycobacterial infection, a treatment with anakinra was chosen instead of anti-TNF-alpha drugs. As soon as the 5th day, anakinra allowed control of fever, then rapid improvement of constitutional symptoms, arthritis, cutaneous lesions, and normalization of C-reactive protein, IL-6, and especially IL-1β levels. Then methotrexate was added, while anakinra was removed at the 12th month, with persistent and complete remission over the two-year follow up. Further assessment of IL-1 pathogenic role and blockade on larger cohorts of patient could open new therapeutic perspectives for refractory/relapsing MRH, considering the good tolerance profile of specific targeting drugs., (Copyright © 2015 Société française de rhumatologie. Published by Elsevier SAS. All rights reserved.)

The literature reports approximately 300 cases of multicentric reticulohistiocytosis (MRH) worldwide, mostly women of Caucasian origin. MRH manifests as a symmetric erosive polyarthritis mimicking rheumatoid arthritis with the subsequent appearance of typical papulonodular skin lesions. The disease may rapidly progress towards mutilans arthritis in the majority of cases, but it generally remits spontaneously in 10 years. The only diagnostic hallmark for MRH is the observation at histology of numerous histiocytes and multinucleated giant cells and ground glass eosinophilic cytoplasm. Despite its rarity, clinical and pathogenetic challenging features characterize the condition. First, the differential diagnosis with other forms of arthritis and the frequent coexistence of neoplasms or autoimmune diseases warrant a careful evaluation of suspected cases. Second, data from isolated MRH cases are consistent in supporting a role for monocyte/macrophage cells and for an enhanced osteoclastic activity in the affected tissues. Third, beside anti-inflammatory treatments, promising reports suggest that biologics targeting TNF-alpha and bisphosphonates may prove beneficial in MRH. Based on these observations, we are convinced that our understanding of this rare condition may prove beneficial in mechanistic advancement for other more prevalent inflammatory conditions such as arthritidies and other bone diseases.

Multicentric reticulohistiocytosis (MRH) is a rare systemic inflammatory granulomatous disease marked by severe and often rapidly progressive polyarticular arthritis and cutaneous papulonodules. Initial clinical diagnosis may be difficult. We describe a 2-year-old girl presenting with pink dermal papules on the forehead, thighs, elbows, knees, and palms of the hands. Based on clinical findings and skin biopsy results, she was initially diagnosed with granuloma annulare. At 5 years of age, she developed arthritis, fatigue, and more widespread skin papules leading to the diagnosis of MRH. To our knowledge, this is the youngest individual with MRH yet described. We outline the timeline and unique features of her case and review the literature pertaining to MRH in children. Although rare, MRH can be permanently debilitating, making prompt diagnosis critical. A standardized approach to investigation and management needs to be developed., (© 2015 Wiley Periodicals, Inc.)