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Competing Interests: Competing interests: None declared.

Erdheim-Chester disease (ECD) is a rare, non-Langerhans cell histiocytosis with diverse clinical features. It is characterized by systemic histiocyte infiltration of the bone, skin, central nervous system, lung, kidney, and cardiovascular system. Pericardial involvement is frequently revealed through either pericardial effusion or pericardial thickening in patients with ECD. Although most patients remain asymptomatic, progressive pericarditis, effusion, or cardiac tamponade may occur. Herein, we report a rare and unusual presentation of ECD in a 51-year-old man who experienced severe constrictive pericarditis. The patient presented with uncontrolled fluid retention and heart failure. After the diagnosis of ECD, interferon alpha treatment was administered. The patient recovered dramatically with decreased pleural and pericardial effusion, as well as improvements in the echocardiographic signs of constrictive pericarditis. Despite several therapeutic options described in the literature for managing ECD-related pericardial disease, a standard treatment has not been established. This report highlights the importance of early treatment based on accurate diagnosis of an unusual ECD complication.

Histiocytoses are rare diseases characterised by infiltration of affected organs by myeloid cells with a monocyte or dendritic cell phenotype. Symptoms can range from self-resolving localised forms to multisystemic lesions requiring specific treatment. To demonstrate extremely rare cases of CD68-negative cardiac histiocytosis with expression of SARS-CoV-2 antigen in infiltrate cells. We demonstrated a case of Erdheim-Chester disease in a 67-year-old man with pericardial involvement and positive dynamics with vemurafenib treatment, an autopsy case of xanthogranulomatous myopericarditis in a 63-year-old man, surgical material of xanthogranulomatous constrictive pericarditis in a 57-year-old man, and an autopsy case of xanthogranulomatosis in a 1-month-old girl. In all cases, xanthogranuloma cells expressed CD163, many of them spike protein SARS-CoV-2, while CD68 expression was detected only in single cells. In this article, we demonstrated four cases of extremely rare CD68-negative cardiac xanthogranulomatosis in three adults and one child with expression of the spike protein SARS-CoV-2 in M2 macrophages. This potential indirect association between COVID-19 and the development of histiocytosis in these patients warrants further investigation. To substantiate this hypothesis, more extensive research is needed.

Purpose: To review all cases of Erdheim-Chester disease (ECD) with orbital involvement treated at Bascom Palmer Eye Institute in Miami, Florida from 2014 to 2022 and compare presentations, treatment modalities, and outcomes., Methods: A retrospective chart review of all patients diagnosed with ECD who presented to Bascom Palmer Eye Institute from 2014 to 2022 was performed. Data collected included demographics, pretreatment history and ophthalmic examination, pathology report, treatment, subsequent examination, and relevant laboratory results. Histopathology, treatments, and outcomes were reviewed and compared between patients., Results: Four cases were included. Primary treatments included vemurafenib (n = 2), cobimetinib (n = 1), and prednisone (n = 1). All patients demonstrated improvement of ophthalmic symptoms. Vemurafenib was the only medical treatment that was tolerated well and resulted in significant improvement in proptosis despite some reported dry eye; all other medications were discontinued due to intolerable side effects., Conclusions: BRAF inhibitors such as vemurafenib have been used as novel therapy in the treatment of ECD. Vemurafenib demonstrated its utility in reducing proptosis in ECD patients at one ophthalmic institution. Vemurafenib may be a favorable treatment option for BRAF -positive ECD patients presenting with orbital disease., Competing Interests: STW is a consultant for Lassen Therapeutics and Immunovant, an advisor for Horizon Therapeutics, and participates in funded research with Horizon Therapeutics, Immunovant, and Sling Therapeutics. The remaining authors have no financial or conflicts of interest to disclose., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.)

Objectives: To present 4 patients with Erdheim-Chester disease (ECD) based on clinical, radiologic, histopathologic, and molecular genetic findings who had enhancing brainstem lesions and were initially believed to have chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids (CLIPPERS)., Methods: Case series., Results: Although patients with ECD can demonstrate clinical and imaging features similar to CLIPPERS, refractoriness to corticosteroids, lack of fulfillment of specific MRI criteria (i.e., enhancing lesions >3 mm, T2 abnormalities that exceed areas of T1 postgadolinium enhancement), and systemic findings such as "hairy kidney" appearance and metadiaphyseal osteosclerosis on 18 F-fluorodeoxyglucose PET-CT help discriminate it from CLIPPERS., Discussion: ECD is a histiocytic neoplasm characterized by multiorgan infiltration of clonal histiocytes carrying activating variants of the MAPK-ERK pathway. Neurologic involvement occurs in up to 40% of ECD with frequent brainstem lesions that can mimic acquired neuroinflammatory disorders, such as CLIPPERS. ECD is an important CLIPPERS mimic with distinct pathophysiology and targeted treatments. We highlight the need to consider histiocytic disorders among other alternate diagnoses when findings are not classic for CLIPPERS.

Erdheim-Chester disease (ECD) is a rare form of non-Langerhans cell histiocytosis with unknown aetiology. It is recently recognised to be neoplastic with genetic mutations affecting the mitogen-activating protein kinase pathway. We report a 49-year-old female patient who initially presented in 2012 to a tertiary care centre in Muscat, Oman, with bilateral facial masses. These were removed but later recurred over a period of 10 years. She then presented with xanthelasmas, bone lesions, secondary infertility due to hypothalamic hypogonadism, diabetes insipidus and Hashimoto's hypothyroidism. The facial masses were biopsied and they showed classic morphological features in the form of diffuse infiltration by foamy histiocytes with scattered Touton type of giant cells, patchy lymphocytic infiltrates and dense fibrosis. The patient is stable and is being followed-up. The presented ECD case is particularly interesting due to the recurrent bilateral facial masses. To the best of the authors' knowledge, this is the first documented case in Oman., (© Copyright 2024, Sultan Qaboos University Medical Journal, All Rights Reserved.)

Erdheim-Chester disease (ECD) is a rare histiocytosis that tends to co-exist with other myeloid malignancies. Here, we use genetic and transcriptomic sequencing to delineate a case of co-occurring BRAF V600E -mutated ECD and acute myeloid leukemia (AML), followed by AML remission and relapse. The AML relapse involved the extinction of clones with KMT2A-AFDN and FLT3-ITD, and the predominance of PTPN11-mutated subclones with distinct transcriptomic features. This case report has highlighted the screening for other myeloid malignancies at the diagnosis of ECD and the clinical significance of PTPN11-mutated AML subclones that require meticulous monitoring., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Introduction: Erdheim-Chester disease (ECD) is a rare non-Langerhans histiocytic multisystem disorder, deriving from mononuclear phagocytic cells. It is notoriously challenging to diagnose. Here we present a case of a patient with multisystem ECD., Case Presentation: A 76-year-old female with a history of Hashimoto's thyroiditis who presented with persistent leukocytosis was found to have bilateral renal enlargement with a perinephric mass, a recurrent pericardial effusion, and bilateral pleural effusions. Following biopsies of several sites of involvement, a diagnosis of ECD was made., Discussion: The existing literature on ECD is sparse, and no diagnostic criteria have been put forward due to widely differing presentations, although the most common is skeletal. Definitive diagnosis requires a tissue sample., Conclusions: In presenting our clinical reasoning and approach, we hope to contribute to the existing body of literature on ECD, with the aim of ultimately having sufficient data to compile a diagnostic framework for other clinicians who encounter ECD., (Copyright© Board of Regents of the University of Wisconsin System and The Medical College of Wisconsin, Inc.)

Erdheim Chester Disease (ECD) is a rare histiocytic disorder marked by infiltration of organs with CD68 + histiocytes. ECD stems from mutations of BRAF and MAP2K1 in hematopoietic stem and progenitor cells (HSPCs), which further differentiate into monocytes and histiocytes. Histopathology reveals lipid-containing histiocytes, which test positive for CD68 and CD133 in immunohistochemistry. Signs and symptoms vary and depend on the organ/s of manifestation. Definitive radiological results associated with ECD include hairy kidney, coated aorta, and cardiac pseudotumor. Treatment options primarily include anti-cytokine therapy and inhibitors of BRAF and MEK signaling., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Competing Interests: Declaration of competing interest There were no disclosed potential conflicts of interest related to this article.

Histiocytic diseases arise from MAPK mutations in myeloid progenitors. Depending on whether the progenitor follows a dendritic cell or macrophage/monocyte lineage the final histology results in Langerhans cell histiocytosis, Rosai-Dorfman disease or Erdheim-Chester disease. Commentary on: Friedman et al. Mixed histiocytic neoplasms: A multicentre series revealing diverse somatic mutations and responses to targeted therapy. Br J Haematol 2024;205:127-137., (© 2024 British Society for Haematology and John Wiley & Sons Ltd.)

Objective: To evaluate the heart response of Erdheim-Chester disease (ECD) through continuous follow-up within our large cohort, for which there is a lack of understanding., Methods: We conducted a retrospective analysis of clinical data from patients with ECD with cardiac involvement diagnosed at our centre between January 2010 and August 2023. We assessed the heart response by integrating pericardial effusion and metabolic responses., Results: A total of 40 patients were included, with a median age of 51.5 years (range: 29-66) and a BRAF V600E mutation rate of 56%. The most common imaging manifestations observed were pericardial effusion (73%), right atrium (70%) and right atrioventricular sulcus infiltration (58%). Among 21 evaluable patients, 18 (86%) achieved a heart response including 5 (24%) complete response (CR) and 13 (62%) partial response (PR). The CR rate of pericardial effusion response was 33%, while the PR rate was 56%. Regarding the cardiac mass response, 33% of patients showed PR. For cardiac metabolic response, 32% and 53% of patients achieved complete and partial metabolic response, respectively. There was a correlation between pericardial effusion response and cardiac metabolic response (r=0.73 (95% CI 0.12 to 0.83), p<0.001). The median follow-up was 50.2 months (range: 1.0-102.8 months). The estimated 5-year overall survival was 78.9%. The median progression-free survival was 59.4 months (95% CI 26.2 to 92.7 months). Patients who received BRAF inhibitors achieved better heart response (p=0.037) regardless of treatment lines., Conclusion: We pioneered the evaluation of heart response of ECD considering both pericardial effusion and cardiac metabolic response within our cohort, revealing a correlation between these two indicators. BRAF inhibitors may improve heart response, regardless of the treatment lines., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Competing Interests: Competing interests: RS reports grants from Japan Heart Foundation/Bayer Yakuhin Research Grant Abroad during the conduct of the study. FC received honoraria for consultant and speaker activities from Pfizer Pharma and Alnylam Therapeutics. SvH has been a paid consultant for and/or received honoraria payments from AstraZeneca, Bayer, Boehringer Ingelheim, BRAHMS, Chugai, Grünenthal, Helsinn, Hexal, Novartis, Novo Nordisk, Pfizer, Pharmacosmos, Respicardia, Roche, Servier, Sorin and Vifor. SvH reports research support from Amgen, Boehringer Ingelheim, Pharmacosmos, IMI and the German Center for Cardiovascular Research (DZHK).

Erdheim-Chester disease (ECD) is a rare 'L' (Langerhans) group histiocytic neoplasm that affects a multitude of organ systems, causing osteosclerotic bone lesions, periaortic encasement ('coated' aorta), retroperitoneal fibrosis involving kidneys and ureters ('hairy kidney'), and infiltration of the central nervous system. Cardiovascular involvement can occur in up to 70% of patients and is usually found during computed tomography/magnetic resonance imaging evaluation. When present, cardiovascular symptoms can have wide variability in presentation from asymptomatic to pericarditis, fatal cardiac tamponade, myocardial infarction, conduction abnormalities, heart failure, renal artery stenosis, and claudication. Cardiac involvement found on imaging includes right atrial pseudotumor, right atrioventricular groove infiltration, and pericardial effusions. ECD can involve the large- and medium-sized arteries, often seen as periarterial thickening (commonly coating the aorta) with stenosis/occlusion. Although more cardiovascular ECD cases have begun to be published in the literature, more data are needed on the outcomes of these patients, as well as how cardiovascular manifestations respond to treatment of ECD., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

A radiologically diagnosed tumor in a 29-year-old woman with a fever of around 39 °C was operated on under the suspicion of cholecystitis or a liver abscess. A solid tumor was found in the adrenal gland and resected. The frozen section findings did not reveal a clear diagnosis of entity and assignment. Histologically, the tumor was found to consist of densely clustered large histiocyte-like cells with expression of vimentin, CD68, and CD163 as well as negativity for keratin, langerin, and SMA. We diagnosed xanthogranulomatous adrenalitis and discussed the differential diagnoses (Langerhans cell histiocytosis, Rosai-Dorfman disease, malakoplakia, Erdheim-Chester disease)., (© 2024. The Author(s).)

Erdheim-Chester disease (ECD) is a rare histiocytosis characterized by the foamy CD68+CD1a- histiocytes infiltrating multiple organs and tissues. ECD might be asymptomatic or present with variable manifestations. The diagnosis of ECD requires characteristic radiological findings and pathological features. Herein, we described a 52-year-old female patient who was admitted to our hospital for recurrent pericardial effusion for two months. She has a medical history of papillary thyroid carcinoma (PTC) and underwent a total thyroidectomy two years before admission. The radiological findings suggested a potential diagnosis of ECD. Cytological analysis of the effusion cytology specimen revealed CD68+CD1a - histiocytes, confirming the ECD diagnosis. The BRAF V600E mutation was identified in the histiocytes, prompting the administration of vemurafenib, a BRAF inhibitor. After two months of standard-dose vemurafenib treatment, the disease was well controlled with pericardial effusion regression., Competing Interests: Declaration of competing interest The authors have no conflict of interest., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Rationale: Erdheim-Chester disease (ECD) is a rare multisystemic disease characterized by the infiltration of multiple organs by foamy CD68 + CD1a-histiocytes. The genetic background consists of gain-of-function somatic mutations in the mitogen-activated protein kinase pathway. The purpose of the present paper is to make a contribution to the scientific literature on ECD by reporting our experience with a complex clinical case report, along with a concise review of the literature. We discussed the unusual clinical presentation, the complex diagnostic process and the comparison with other published cases., Patient Concerns: A 70-year-old man presented with arthralgia due to multiple bone areas of sclerosis, first diagnosed with metastases of a prostatic neoplasm. Sequential thorax-abdomen, femoral and homer contrast-enhanced computed tomography (CT) showed pericardial effusion, pulmonary fibrosis, and perirenal fibrous tissue as "hairy kidneys." He underwent. Three bone biopsies were unsuccessful to reach diagnosis., Diagnoses: A xanthelasma biopsy showed histopathological signs compatible with ECD; genetic analysis showed the mutation BRAFV600E., Interventions: The patient underwent targeted therapy with vemurafenib (BRAF-inhibitor), discontinued 2 weeks later due to the onset of a diffuse erythematous papular rash on the trunk and limbs., Outcomes: At the 1-year follow-up, there was only progression of chronic kidney disease (CKD)., Lessons: The present case report describes how ECD diagnosis could represent a challenge for clinicians, owing to its heterogeneous clinical presentation. Early diagnosis followed by prompt therapy is essential for modifying the natural history of the disease., Competing Interests: The authors have no funding and conflicts of interest to disclose., (Copyright © 2024 the Author(s). Published by Wolters Kluwer Health, Inc.)

Competing Interests: The author declares no conflict of interest.

Histiocytoses, including Langerhans cell histiocytosis (LCH) and Erdheim-Chester disease (ECD), are inflammatory myeloid tumors in which monocyte lineage cells aggregate in various organs, causing tissue damage. Most of these tumors harbor oncogenic mutations in mitogen-activated protein kinase (MAPK) pathway genes, typified by BRAF V600E . Some patients with LCH develop bilateral symmetrical cerebellar lesions and brain atrophy several years after diagnosis when the initial symptoms disappear, leading to cerebellar ataxia and higher cerebral dysfunction. A similar neurological disorder has also been reported in ECD. This neurological disorder can be improved with MAPK inhibitors. When patients with this neurological disorder are identified among neurodegeneration of unknown etiology or histiocytosis patients and treated early with MAPK inhibitors, the disorder can be reversible.

Histiocytic neoplasms (HNs) include juvenile xanthogranuloma, Erdheim-Chester disease, Rosai-Dorfman disease, ALK-positive histiocytosis, and histiocytic sarcoma in the 5th edition of the World Health Organization Classification of Haematolymphoid Tumours. These entities are clinicopathologically distinctive, and typical histological findings have been established. However, the common feature of a proliferation of histiocytic cells often leads to morphological overlap among HNs, and also necessitates a differential diagnosis from several non-HNs or non-neoplastic conditions. In this review, we provide a brief summary of the clinical findings, molecular features, histopathologies, and immunophenotypes of HNs, as well as to discuss their differential diagnosis.

Competing Interests: Declaration of Competing Interest The authors have no conflict of interest to declare.

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis (LCH) that results in multiorgan disease involving the skin, bones, lungs, and kidneys. Female reproductive system manifestation of ECD was rare. Herein, we report a case of ECD involving the left ovary and fallopian tube. A 69-year-old woman presented with abdominal pain for 20 days. Magnetic resonance imaging revealed a solid and cystic mass on the left pelvic cavity. Histological examination revealed ovarian and fallopian tube infiltration by abundant histiocytes, with single small nuclei and foamy cytoplasm, reactive small lymphocytes, and plasma cells. Based on histopathological and immunohistochemical findings of positivity for CD68, CD163, and BRAF V600E and negativity for CD1α and S100, the molecular finding of BRAF V600E mutation, the patient was diagnosed with ECD. Positron emission tomography examination did not reveal any other lesions. The patient recovered well 12 months after surgery without any treatment. ECD involving the left fallopian tube and ovary was rare and needed to be differentiated from LCH, Rosai-Dorfman disease (RDD), juvenile xanthogranuloma (JXG), IgG4 + -related disease (IgG4 + RD), and metastatic signet ring cell carcinoma., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

BACKGROUND Erdheim-Chester disease (ECD), a form of non-Langerhans-cell histiocytosis, is extremely rare. The mean age of individuals with ECD is in their 50s. Histiocytic infiltration of vital organ systems is a potential cause of substantial morbidity, which is associated with the multisystemic form of ECD. This report presents the first case of ECD with renal abnormalities in Palestine. CASE REPORT A 54-year-old woman with no medical or surgical history presented with 6 months of bilateral flank pain with no radiation or fever. A physical examination revealed only bilateral flank pain. Urine tests showed microhematuria. Laboratory test results showed increased serum creatinine levels (1.21 mg/dL) and microcytic anemia. A CT scan revealed significant multi-organ abnormalities, including renal abnormalities with a hairy kidney sign, pericardial effusion, and an osteolytic lesion of the spine. The hairy kidney sign is pathognomonic for ECD, so the renal mass was biopsied to confirm the diagnosis. The biopsy showed foamy histiocytes, lymphocytes, and plasma cells. Foamy histiocytes were CD68-positive and negative for S100, CD1a, and HMB45. PAx5 and CD3 immunostaining showed T-predominant B-lymphocyte mixtures. CONCLUSIONS In the setting of systemic symptoms and imaging abnormalities such as presence of the hairy kidney sign, pericardial effusion, and osteolytic lesion of the spine, it is necessary to examine the possibility of ECD and proceed with a biopsy for confirmation. This is the first case in Palestine to be reported and the second case worldwide with a renal mass as an atypical presentation.

Background: Erdheim Chester disease (ECD) is a rare disease with multisystemic involvement in the group of non-langerhans cell histiocytosis. Although nearly 100 years have passed since its definition, the number of cases reported all over the world is below 1000. In addition to the rarity of the disease, low awareness seems to play a role in this., Case Presentation: 47-year-old white caucasian women patient who presented to our clinic with symptoms of weakness-fatigue as well as increasing pain in the knees and ptosis in the left eye. Result of the patient's bone biopsy, ECD was considered pathologically and BRAF V600E mutation was shown molecularly. After presenting the clinical, laboratory and other examination results of the case, the dramatic response seen with targeted therapy will be discussed., Conclusions: BRAF V600E mutation is frequently seen in ECD. Vemurafenib plays an active role in targeted therapy., (© 2023. BioMed Central Ltd., part of Springer Nature.)

We report a case of BRAF-mutation positive Erdheim-Chester disease presenting with a cerebellar ataxia. This is the first such case to be reported without structural MRI abnormalities but with a single intrathecally produced oligoclonal band. Now that the histiocytoses have been recharacterised as neoplastic, we speculate that the mechanism of the ataxia in our case is paraneoplastic. We highlight the importance of searching for BRAF mutations in this disease, as their presence leads to effective personalised treatments., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2023. No commercial re-use. See rights and permissions. Published by BMJ.)

Purpose: The authors aim to describe the ophthalmologic manifestations of pediatric Erdheim-Chester disease (ECD)., Methods: The authors describe a novel case of ECD presenting as isolated bilateral proptosis in a child and provide a comprehensive review of the documented pediatric cases to observe overall trends and ophthalmic manifestations of disease. Twenty pediatric cases were identified in the literature., Results: The mean age at presentation was 9.6 years (1.8-17 years) with a mean time of symptom presentation to diagnosis of 1.6 years (0-6 years). Nine patients (45%) had ophthalmic involvement at diagnosis, 4 who presented with ophthalmic complaints: 3 with observable proptosis and 1 with diplopia. Other ophthalmic abnormalities included eyelid findings of a maculopapular rash with central atrophy on the eyelids and bilateral xanthelasmas, neuro-ophthalmologic findings of a right hemifacial palsy accompanied by bilateral optic atrophy and diplopia, and imaging findings of orbital bone and enhancing chiasmal lesions. No intraocular involvement was described, and visual acuity was not reported in most cases., Conclusions: Ophthalmic involvement occurs in almost half of documented pediatric cases. Typically presenting with other symptoms, the case highlights that isolated exophthalmos may be the only clinical sign, and ECD should be included in the differential diagnosis of bilateral exophthalmos in children. Ophthalmologists may be the first to evaluate these patients, and a high index of suspicion and an understanding of the varied clinical, radiographic, pathologic, and molecular findings are critical for prompt diagnosis and treatment of this unusual disease., Competing Interests: The authors have no financial or conflicts of interest to disclose., (Copyright © 2023 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.)

Histiocytosis is a group of rare diseases characterized by inflammation and accumulation of cells derived from monocytes and macrophages in different tissues. The symptoms are highly variable, from mild forms with involvement of a single organ to severe multisystem forms that can be life compromising. The diagnosis of histiocytosis is based on the clinic, radiological findings and pathological anatomy. A biopsy of the affected tissue is recommended in all cases as it may have therapeutic implications. During the last decade, some mutations have been identified in the affected tissue that condition activation of the MAPK/ERK and PI3K/AKT pathway, in a variable proportion depending on the type of histiocytosis. In this review we mainly focus on Langerhans Cell Histiocytosis, Erdheim-Chester Disease and Rosai-Dorfman Disease., (Copyright © 2023 Elsevier España, S.L.U. All rights reserved.)

Erdheim-Chester disease (ECD) and Rosai-Dorfman disease (RDD) are rare non-Langerhans cell histiocytoses (non-LCHs), for which therapeutic options are limited. MAPK pathway activation through BRAFV600E mutation or other genomic alterations is a histiocytosis hallmark and correlates with a favorable response to BRAF inhibitors and the MEK inhibitor cobimetinib. However, there has been no systematic evaluation of alternative MEK inhibitors. To assess the efficacy and safety of the MEK inhibitor trametinib, we retrospectively analyzed the outcomes of 26 adult patients (17 with ECD, 5 with ECD/RDD, 3 with RDD, and 1 with ECD/LCH) treated with orally administered trametinib at 4 major US care centers. The most common treatment-related toxicity was rash (27% of patients). In most patients, the disease was effectively managed at low doses (0.5-1.0 mg trametinib daily). The response rate of the 17 evaluable patients was 71% (73% [8/11] without a detectable BRAFV600E achieving response). At a median follow-up of 23 months, treatment effects were durable, with a median time-to-treatment failure of 37 months, whereas the median progression-free and overall survival were not reached (at 3 years, 90.1% of patients were alive). Most patients harbored mutations in BRAF (either classic BRAFV600E or other BRAF alterations) or alterations in other genes involved in the MAPK pathway, eg, MAP2K, NF1, GNAS, or RAS. Most patients required lower than standard doses of trametinib but were responsive to lower doses. Our data suggest that the MEK inhibitor trametinib is an effective treatment for ECD and RDD, including those without the BRAFV600E mutation., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Background: Erdheim-Chester disease (ECD) is a rare histiocytic disorder characterized by multisystem xanthogranulomatous infiltration by lipid-laden histiocytes. We report two cases of ECD involving the orbit and describe their clinicopathologic factors, treatments, and prognosis. One was a rare case of ECD complicated with primary thrombocytosis., Case Presentation: This study describes two patients with bilateral orbital ECD. Both presented with proptosis and visual loss; imaging findings showed bilateral intraorbital masses. Both had different degrees of systemic symptoms (pleural effusion, pericardial effusion, ascites, and heart failure) before the ocular symptoms and did not find the cause before ophthalmic tumor resection and pathological biopsy. The diagnosis of ECD was confirmed after pathological biopsy and detection of BRAF V600E mutation. Patient 2 also with primary thrombocytosis and had a CALR mutation as well as the BRAF V600E mutation. Both patients were recommended to receive targeted therapy. Patient 1 refused targeted therapy for financial reasons and was discharged after local radiotherapy only. The patient had no light perception in either eye and no improvement in systemic symptoms. Patient 2 began targeted treatment after diagnosis and reached the discharge criteria 2 weeks later. He is in good condition at present, but unfortunately, his eyesight has not improved because of the irreversible damage to his visual function., Conclusion: ECD is easily misdiagnosed and missed because of its rarity and diverse clinical manifestations. Orbital involvement is common in ECD, and surgery is the most frequently employed approach. Despite the surgical resection is not curative, its significance lies in biopsy to establish diagnosis and/or surgical debulking to relieve mass effect, minimizing further impairment of visual function. Targeted therapy is the most effective treatment for patients with a positive BRAF mutation gene. Evaluation of a concomitant myeloid neoplasm is also critical before initiating targeted therapies for refractory ECD., (© 2023. The Author(s).)

Erdheim-Chester disease (ECD) is a rare type of non-Langerhans cell histiocytosis. However, its prevalence has increased significantly the past few years due to increased awareness about the disorder, and 1500 cases have been reported worldwide. It is often a multisystemic disease with skeletal, cardiovascular, urologic, renal, retroperitoneal, pulmonary, endocrine, cutaneous, and neurologic involvement. MAPK pathway mutations, such as BRAF activating and MAP2K1 mutations, play a key role in its pathogenesis. In addition to the characteristic clinical, radiological, and histopathological findings, identifying underlying mutations helps diagnose and treat patients with highly effective targeted therapies such as BRAF and MEK inhibitors. We report a case of a man, aged 55 years, with an extensive and prolonged course of an unexplained multisystemic disease, later diagnosed with BRAF V600E-negative and MAP2K1-positive ECD on cell-free DNA testing. Additionally, we review common clinical manifestations, mutations, diagnoses, and targeted therapies for ECD.

Diagnosis of histiocytosis can be difficult and one of the biggest challenges is to distinguish between reactive and neoplastic histiocytes on histology alone. Recently, OCT2 nuclear expression was reported in Rosai-Dorfman disease (RDD). Our purpose was to expand the testing of OCT2 on a broader variety of sporadic or H syndrome-related histiocytoses. Cases of histiocytoses were retrieved from the files of Ambroise Paré Pathology Department. All slides and molecular analyses were reviewed, and staining was completed with immunohistochemistry for OCT2. A total of 156 samples from different localizations were tested. Among sporadic cases, 52 patients had RDD, and 10 patients had mixed histiocytosis combining RDD with Erdheim Chester disease (ECD, n = 8), Langerhans cell histiocytosis (LCH, n = 2) or juvenile xanthogranuloma (JXG, n = 1). All these patients were positive for OCT2 in RDD characteristic histiocytes. Twenty-three patients had ECD and all but two (91% - 21/23) were negative for OCT2. By contrast, OCT2 was positive in 11/27 (41%) LCH and 6/16 (38%) JXG. Among the 10 samples of H syndrome-associated histiocytosis, 3 had typical RDD histology, 6 had unclassified histiocytosis, and one had mixed RDD-LCH; all were positive for OCT2. On 16 samples of granulomatous lymphadenitis, OCT2 was negative in epithelioid histiocytes. Our study shows that OCT2 has a sensitivity of 100% for RDD cases and mixed histiocytoses with an RDD component. It is negative in 92% of ECD but expressed in at least 38% of LCH, JXG, and C group histiocytoses. Finally, OCT2 is positive in all H syndrome-related histiocytoses, independent of their histology., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose of Review: Histiocytic disorders, including Erdheim-Chester disease (ECD), Langerhans cell histiocytosis (LCH), and Rosai-Dorfman disease (RDD), are rare neoplasms that may present with a spectrum of neurologic involvement. Diagnostic delay is common due to heterogeneity in presentation and challenging pathology., Recent Findings: Recent advances in the treatment of these diseases targeted towards mutations in the MAP kinase pathway have led to an improved prognosis in these patients with neurologic involvement. It is critical for clinicians to have a high index of suspicion to allow for early targeted treatment and optimize neurologic outcomes. A systematic approach to diagnosis is presented in this article to allow for accurate diagnosis of these rare diseases., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Rationale: Erdheim-Chester disease (ECD) is a rare progressive disease affecting multiple systems. It has recently been recognized as a neoplastic disease following the discovery of activating mutations in the MAPK pathway. There are several striking signs of ECD, such as the long bone involvement, as well as the hairy kidney appearance on computed tomography scan. It is rare for ECD to manifest neurological symptoms. Central nervous system involvement is a strong prognostic factor and independent predictor of death. ECD is characterized by the overproduction and accumulation of foamy histiocytes and Touton's giant cells in various tissues and organs. ECD is a multisystem disorder in which any organ may be affected., Patient Concerns: This case report describes a 57-year-old woman with headaches and ataxia as the first clinical manifestation, without characteristic bone pain, but with delayed enuresis. In addition to the renal involvement, this patient had rarer splenic involvement., Diagnoses: The imaging presentation of this patient was similar to that of a "multiple meningiomas". A combination of clinical, imaging and pathology for the diagnosis of ECD., Interventions: Patients were given INF-α therapy., Outcomes: Fortunately, the patient responded well to INF-α treatment., Lessons: ECD patient with neuro-endocrine symptoms., Competing Interests: The authors have no funding and conflicts of interest to disclose., (Copyright © 2023 the Author(s). Published by Wolters Kluwer Health, Inc.)