Effective BRAF inhibitor vemurafenib therapy in a 2-year-old patient with sequentially diagnosed Langerhans cell histiocytosis and Erdheim-Chester disease

One Health: Therapies Targeting Genetic Variants in Human and Canine Histiocytic and Dendritic Cell Sarcomas

The precise cause of HS/DCS is still unknown. The relatively low incidence in humans urges for an animal model with a high incidence to accelerate knowledge about genetics and optimal treatment of HS/DCS. Namely, until now, the therapies targeting genetic variants are still more experimental and sparsely used, while consensus is missing. In addition, the literature about variants and possible mutation-targeted therapies in humans and dogs consists mainly of case reports scattered throughout the literature. Therefore, an overview is provided of all currently known genetic variants in humans and dogs with HS/DCS and its subtypes, their possible mutation-targeted therapies, their efficacy, and a contemplation about the future. Several genetic variants have already been discovered in HS/DCS, of which many are shared between canine and human HS/DCS, but unique variants exist as well. Unfortunately, none of these already found variants seem to be specifically causal for HS/DCS, and the puzzle of its landscape of genetic variation is far from complete. The use of mutation-targeted therapies, including MAPK-/MEK-inhibitors and the future use of PTPN11-, CDK4/6- and PD-1-inhibitors, seems to be promising for these specific variants, but clearly, clinical trials are needed to determine optimal inhibitors and standardised protocols for all variants. It can be concluded that molecular analysis for variants and subsequent mutation-targeted therapy are an essential addition to cancer diagnostics and therapy. A joint effort of humans and dogs in research is urgently needed and will undoubtedly increase knowledge and survival of this devastating disease in dogs and humans.

Treatment of Langerhans Cell Histiocytosis and Histiocytic Disorders: A Focus on MAPK Pathway Inhibitors

Histiocytic disorders are rare diseases defined by the clonal accumulation of a macrophage or dendritic cell origin. These disorders include Langerhans cell histiocytosis, Erdheim-Chester disease, juvenile xanthogranuloma, malignant histiocytoses, and Rosai-Dorfman-Destombes disease. These histiocytic disorders are a diverse group of disorders with different presentations, management, and prognosis. This review focuses on these histiocytic disorders and the role of pathological ERK signaling due to somatic mutations in the mitogen--activated protein kinase (MAPK) pathway. Over the last decade, there has been growing awareness of the MAPK pathway being a key driver in many histiocytic disorders, which has led to successful treatment with targeted therapies, in particular, BRAF inhibitors and MEK inhibitors.

PET/MR of pediatric bone tumors: what the radiologist needs to know

Integrated 2-deoxy-2-[fluorine-18]fluoro-D-glucose (18F-FDG) positron emission tomography (PET)/magnetic resonance (MR) imaging can provide "one stop" local tumor and whole-body staging in one session, thereby streamlining imaging evaluations and avoiding duplicate anesthesia in young children. 18F-FDG PET/MR scans have the benefit of lower radiation, superior soft tissue contrast, and increased patient convenience compared to 18F-FDG PET/computerized tomography scans. This article reviews the 18F-FDG PET/MR imaging technique, reporting requirements, and imaging characteristics of the most common pediatric bone tumors, including osteosarcoma, Ewing sarcoma, primary bone lymphoma, bone and bone marrow metastases, and Langerhans cell histiocytosis.

Efficacy and safety of vemurafenib in Langerhans cell histiocytosis (LCH): A systematic review and meta-analysis

Almost half of the patients with Langerhans cell histiocytosis (LCH) are refractory to primary induction chemotherapy or undergo reactivation. The ideal treatment modality for refractory/relapsed LCH is yet not evidenced. This review aimed to determine the efficacy and safety of vemurafenib (a BRAF pathway inhibitor) in LCH, particularly the refractory/relapsed cases. The literature search was conducted using PubMed, Embase, CENTRAL, and abstracts published in the SIOP meetings. Studies that described the outcome of patients of LCH being treated with vemurafenib, alone or in combination, were included. A total of 416 studies were screened, and after applying exclusion criteria, 22 studies (n = 107) were included in the final analysis. The first-line therapy was prednisolone plus vinblastine for most patients (n = 92, 86%), and vemurafenib was started upfront in 3 patients (3%). The median time to first clinical response with vemurafenib was one week. The median time to best response was 5.25 months. Out of 107 patients, 62 patients (58%) had ultimately no active disease (NAD) while 39 (36%) had active disease better (ADB), making the overall response rate (ORR) of 101/107, ie, 94.4% (CI 0.88; 0.98). The main adverse effects of vemurafenib were rash or photosensitivity (47%) and other cutaneous adverse events (15%). Vemurafenib is highly efficacious and safe in the treatment of refractory LCH; however, the timing of its commencement and duration of therapy is yet to be established. Larger prospective collaborative trials are needed to answer the appropriate treatment duration and effective maintenance therapy approach.

Signaling pathways, microenvironment, and targeted treatments in Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid malignancy in the "L-group" histiocytosis. Mitogen-activated protein kinase (MAPK) pathway activating mutations are detectable in nearly all LCH lesions. However, the pathogenic roles of MAPK pathway activation in the development of histiocytosis are still elusive. This review will summarize research concerning the landscape and pathogenic roles of MAPK pathway mutations and related treatment opportunities in Langerhans cell histiocytosis. Video abstract.

Tissue-Agnostic Activity of BRAF plus MEK Inhibitor in BRAF V600-Mutant Tumors

BRAF plus MEK inhibitor combinations are currently FDA-approved for melanoma, non-small cell lung cancer, and anaplastic thyroid cancer. The lack of clinical benefit with BRAF inhibition in BRAF V600-mutated colorectal cancer has prevented its tissue-agnostic drug development. We reviewed the AACR GENIE database for the prevalence of BRAF V600 mutations across tumor types. We reviewed the literature for case reports of clinical responses, outcomes in patients with BRAF V600 mutation-positive nonmelanoma malignancies who received BRAF inhibitor therapy, and data from published adult and pediatric trials. BRAF V600 mutations are prevalent across multiple nonmelanoma malignancies (>40 different tumor types), lead to oncogene addiction, and are clinically actionable in a broad range of adult and pediatric nonmelanoma rare malignancies. Continued tissue-agnostic drug development is warranted beyond the current BRAF plus MEK approved cancers.

Erdheim-Chester disease: First pediatric case report in Colombia

The Erdheim-Chester’s disease is extremely rare in children. We present the case of a 12-year-old girl with histological and radiological diagnosis of this disease and mutation of the BRAF gene, who developed multisystemic compromise requiring treatment with dabrafenib. We identified 22 reports of this condition among children worldwide and this is the second pediatric case in Latin America. Diagnostic imaging is critical to confirm Erdheim-Chester disease and for the surgical planning of the biopsy. Additionally, we identified the parasellar dark sign, which has previously been reported on lymphocytic hypophysitis. This report contributes to the current practice as it shows the clinical presentation and the diagnostic workout of this disease in pediatrics.

Mitogen-activating protein kinase pathway alterations in Langerhans cell histiocytosis

PURPOSE OF REVIEW

Langerhans cell histiocytosis (LCH) is a rare disorder characterized by the infiltration of involved tissues by specialized dendritic cells. The demonstration of the constant activation of the mitogen-activated protein kinase (MAPK) pathway in LCH lesions has been a breakthrough in the understanding of the pathogenesis of this rare disease. We will summarize the current knowledge on MAPK alterations in LCH and the new therapeutic options indicated by these findings.

RECENT FINDINGS

Since the description of the B-Raf proto-oncogene, serine/threonine kinase (BRAF)V600E mutation in LCH lesions, several other molecular alterations affecting the MAPK pathway have been identified in most cases. Based on these driver alterations, LCH cells were shown to be derived from hematopoietic precursors, which yielded the current concept of LCH as a myeloid inflammatory neoplasia. MAPK pathway inhibitors have emerged as an innovative therapy in severe forms of LCH, resulting in virtually no acquired resistance. However, although they are highly effective, their effect is only temporary, as the disease relapses upon discontinuation of the treatment.

SUMMARY

LCH is an inflammatory myeloid neoplastic disorder, driven by mutations activating the MAPK pathway. MAPK-targeted treatments represent an important stepforward in the management of patients with severe progressive LCH.

Erdheim-Chester disease: a comprehensive review from the ophthalmologic perspective

Erdheim-Chester disease (ECD) is a rare clonal histiocytic neoplasm with less than 1200 documented cases to date. The disease is life-threatening and difficult to recognize, although increasing awareness as well as the integration of clinical, imaging, pathology information , and genetic studies have led to a recent exponential increase in new reported cases. ECD affects multiple organs and systems, including skeletal, neurologic, and cardiovascular. Pulmonary, retroperitoneal, and cutaneous lesions have also been reported in various combinations. Until the discovery that more than half of ECD patients harbor the BRAF-V600E mutation or other mutations in the mitogen-activated protein kinase (MAPK) and RAS pathways, Interferon-a was the first-line treatment. Nowadays BRAF and MEK-inhibitors targeted therapies are the mainstay of treatment. Ophthalmologic involvement occurs in 25% -30% of ECD cases, usually in the form of orbital involvement presenting with exophthalmos and ophthalmoplegia. Other ophthalmologic manifestations include palpebral xanthelasmas, anterior uveitis and vitritis, optic disk edema, choroidal infiltration, recurrent serous retinal detachment, retinal drusen-like deposits and retinal pigment epithelial changes. ECD patients can also present with ocular symptoms as a result of adverse effects of the treatment regimens. In some cases with smoldering or protean symptoms, the emergence of eye manifestations triggered the diagnosis. Ophthalmologists have to be aware of the disease, recognize the constellation of ECD symptoms, and contribute to the diagnosis, treatment, and follow-up of ECD patients.

Mixed Langerhans Cell Histiocytosis and Erdheim-Chester Disease in a Girl: A Rare and Puzzling Diagnosis

OBJECTIVE

The objective of this study was to report the case of a girl diagnosed as suffering from multisystem, BRAF V600E-positive refractory Langerhans cell histiocytosis (LCH) and coexistent Erdheim-Chester disease (ECD) with perirenal, intracranial involvement and the dramatic response to clofarabine treatment.

OBSERVATIONS

Histiocytoses are rare diseases with a broad clinical spectrum. Recent evidence supports a molecular and clinical overlap between LCH and ECD, and mixed LCH/ECD is now a separate entity. However, only a few pediatric cases of mixed disease have been reported in the literature.

CONCLUSIONS

In a child with refractory, multisystem histiocytosis and atypical presentations, mixed LCH/ECD should be suspected in the differential diagnosis.

The triptych of mixed histiocytosis: a systematic review of 105 cases and proposed clinical classification

Histiocytoses are one of the ultimate diagnostic challenges that every physician face at least once in his/her life. Giving their protean manifestation and differentiated therapeutic needs, histiocytosis requires extensive characterization and multidisciplinary management. Mixed histiocytosis is an emerging group of syndromes defined by the overlap of Langerhans cell histiocytosis and another histiocytic disorder of different type. Despite rare, it may account for up to a fifth of systemic histiocytosis patients in some series. In this work, we comprehensively review for the first time the clinical, radiological, histopathological and molecular features of mixed histiocytosis in children and adults. Moreover, we propose a clinical classification in three groups that differentiate patients with systemic involvement and worse overall survival to other groups with more localized manifestations and indolent behavior, wanting to ease their recognition and treatment. Interestingly we also found that mixed histiocytosis harbor BRAFV600E mutations with a higher frequency comparing to all other histiocytoses, and may therefore benefit of specific inhibitory drugs.

Effective High-dose Interferon-α Therapy in a 13-Year-Old Girl With Erdheim-Chester Disease

Erdheim-Chester disease (ECD) is a proliferative disorder of non-Langerhans histiocytes with a higher incidence in the fifth to seventh decades and rarer occurrence in the pediatric population. Although ECD typically involves bone, it can also affect the central nervous system, cardiovascular system, retro-orbital space, retroperitoneal space, and kidneys, lungs, and skin. A 13-year-old Syrian girl who presented with multisystemic involvement was diagnosed with ECD. The B-Raf proto-oncogene V600E mutation was not detected in ECD lesions. Response to the high-dose interferon-α therapy was excellent in this pediatric patient. In this article, pediatric ECD case reports are also reviewed.

[Giant cell tumor of bone : Morphology, molecular pathogenesis, and differential diagnosis]

The histological picture of giant cell tumor of bone is characterized by numerous osteoclast-like giant cells. However, these are not the actual tumor cells, but constitute a reactive infiltrate. Rather, the tumor cells are mononuclear mesenchymal cells, which even reveal an osteoblastic line of differentiation. The CD68-positive macrophages form the second group of mononuclear cells. The receptor activator of nuclear factor kappa-B/ligand (RANK/RANKL) system, which belongs to the tumor necrosis factor (TNF) cytokine family, is decisively involved in the activation of the giant cells. It is generally accepted that a RANKL expression of mononuclear stromal cells is responsible for the development and differentiation of osteoclast-like giant cells. Therefore, the RANKL inhibitor denosumab constituted an essential element for giant cell tumor therapy over the last several years, as it blocks the maturation of osteoclasts and thus the osteolytic activity and the spread of tumor. However, with time it became evident that the not risk-free therapy with denosumab may lead to extensive recurrences upon withdrawal, so this therapy is applied with caution today.At the molecular genetic level, the giant cell tumors of bone are characterized by point mutations in the H3F3A gene. The detection of this mutation is used for the diagnostic differentiation from other bone lesions containing giant cells. Giant cell osteosarcomas rarely contain H3F3A mutations. Chondroblastoma is characterized by mutations in the H3F3B gene.

MAPK mutations and cigarette smoke promote the pathogenesis of pulmonary Langerhans cell histiocytosis

Pulmonary Langerhans cell histiocytosis (PLCH) is a rare smoking-related lung disease characterized by dendritic cell (DC) accumulation, bronchiolocentric nodule formation, and cystic lung remodeling. Approximately 50% of patients with PLCH harbor somatic BRAF-V600E mutations in cells of the myeloid/monocyte lineage. However, the rarity of the disease and lack of animal models have impeded the study of PLCH pathogenesis. Here, we establish a cigarette smoke-exposed (CS-exposed) BRAF-V600E-mutant mouse model that recapitulates many hallmark characteristics of PLCH. We show that CD11c-targeted expression of BRAF-V600E increases DC responsiveness to stimuli, including the chemokine CCL20, and that mutant cell accumulation in the lungs of CS-exposed mice is due to both increased cellular viability and enhanced recruitment. Moreover, we report that the chemokine CCL7 is secreted from DCs and human peripheral blood monocytes in a BRAF-V600E-dependent manner, suggesting a possible mechanism for recruitment of cells known to dominate PLCH lesions. Inflammatory lesions and airspace dilation in BRAF-V600E mice in response to CS are attenuated by transitioning animals to filtered air and treatment with a BRAF-V600E inhibitor, PLX4720. Collectively, this model provides mechanistic insights into the role of myelomonocytic cells and the BRAF-V600E mutation and CS exposure in PLCH pathogenesis and provides a platform to develop biomarkers and therapeutic targets.

Primary oral manifestation of Langerhans cell histiocytosis refractory to conventional therapy but susceptible to BRAF-specific treatment: a case report and review of the literature

Langerhans cell histiocytosis (LCH) is a diagnostic and therapeutic challenge. We report on a rare case of its primary oral manifestation that was treated successfully with the BRAF-specific agent, vemurafenib, after insufficient standard LCH treatment. This case underlines the importance of proper diagnosis and the evaluation of targeted therapy as a valuable tool in LCH treatment. Furthermore, the close collaboration of surgeons, oncologists, and dentists is mandatory to ensure adequate treatment, restore the stomatognathic system in debilitating post-treatment situations, improve quality of life, and ensure effective disease control in infants and young patients.

Erdheim Chester disease in a patient with Burkitt lymphoma: a case report and review of literature

Background

Erdheim Chester disease (ECD) is a rare, non-Langerhans cell histiocytosis characterized by widespread tissue infiltration by CD68-positive, CD1a-negative foamy histiocytes. ECD can be difficult to identify, and diagnosis relies on the presence of histiocytes with certain histologic and immunophenotypic features in an appropriate clinical and radiologic setting. Clinical signs and symptoms are variable depending on which organ systems are involved. Most patients have at least skeletal involvement with bone pain as well as fatigue. Other common manifestations include diabetes insipidus, cardiac, periaortic, or retro-orbital infiltration/fibrosis, kidney impairment, xanthelasmas, among others.

Case presentation

Herein, we describe a case of BRAF-mutation positive ECD in a patient with Burkitt lymphoma, and we review recent literature.

Conclusion

Underlying BRAF and other MAPK pathway mutations are identified in approximately 50% of cases of ECD, which aids in diagnosis as well as enables novel targeted treatments. ECD patients have an increased risk of myeloid neoplasms; however, unlike other histiocytoses, an association with lymphoproliferative disorders has not been recognized.

A novel fusion gene PLEKHA6-NTRK3 in langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is the most common histiocytosis with constitutive activation of the RAS–RAF–MEK–ERK (MAPKinase) cell signaling pathway. We analyzed 89 cases of BRAF and MAP2K1 mutations by Sanger sequencing, of which 18 cases showed that these two gene mutations are negative. Whole genome sequencing of suitable specimens in these negative cases revealed a translocation from the 3 intron of PLEKHA6 to the 13 intron of NTRK3 in one case. We identified that this translocation could cause a novel fusion mutation, PLEKHA6‐NTRK3. Overexpression of the PLEKHA6‐NTRK3 mutant in NIH 3T3 cells enhanced MAPKinase pathway activation, promote cell growth. Our result suggested that a new mutation need be included in LCH molecular screening panel to better define its prevalence in LCH.

What's new?

Langerhans cell histiocytosis (LCH) is a rare immune and neoplastic disorder. While it is known as the most common histiocytosis with constitutive activation of the RAS‐RAF‐MEK‐ERK (MAPKinase) cell signaling pathway, its pathogenesis remains obscure. Here, whole‐genome sequencing of BRAF V600E‐negative and MAP2K1‐negative LCH cases revealed a translocation from the intron 3 of PLEKHA6 to the intron 13 of NTRK3 in one patient, identifying a novel fusion mutation. Overexpression of PLEKHA6‐NTRK3 in vitro enhanced MAPKinase pathway activation, promoting cell growth. The results support the inclusion of the fusion mutation in LCH molecular screening panel to better define its prevalence in patients.

Resolved heart tamponade and controlled exophthalmos, facial pain and diabetes insipidus due to Erdheim-Chester disease

A 69-year-old woman suffering from exophthalmos and facial pain came to us referred for aetiological diagnosis of exophthalmos. Orbital MRI showed thinned extrinsic ocular musculature, intraconal fat infiltration, retro-ocular compression and thickening of maxillary and sphenoid sinus walls. She had been suffering from diabetes insipidus for the last 7 years. During our diagnosis process, she presented signs of cardiac tamponade. Transthoracic heart ultrasound revealed large pericardial effusion and a heterogeneous mass that compressed the right ventricle. No osteosclerotic lesions on appendicular bones were present. Pericardiocentesis temporarily controlled tamponade and corticoid therapy temporarily abated exophthalmos. Pericardiectomy definitively resolved tamponade. Histological examination of pericardial tissue was conclusive of Erdheim-Chester disease. Exophthalmos responded to pegylated interferon-alpha-2a. Facial bone pain disappeared after zoledronic acid and interferon treatment. During interferon therapy, the patient suffered from a severe generalised desquamative exanthema that slowly resolved after discontinuing interferon. Diabetes insipidus remains controlled with desmopressin.

Dramatic efficacy of dabrafenib in Erdheim-Chester disease (ECD): a pediatric patient with multiple large intracranial ECD lesions hidden by refractory Langerhans cell histiocytosis

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell form of histiocytosis that can affect the central nervous system. ECD predominantly affects adults, and only a few pediatric cases have been reported. The co-occurrence of ECD and Langerhans cell histiocytosis (LCH) is exceedingly rare. An 11-year-old boy, who was diagnosed with LCH 7 years previously, presented with multiple giant intracranial lesions. At the time of his initial diagnosis, only one intracranial lesion was observed, and it began to enlarge. Currently, up to 7 intracranial lesions can be observed in this patient. However, the diagnosis of ECD was not confirmed until this most recent open resection. The BRAF V600E mutation was detected in both LCH and ECD lesions. Dabrafenib therapy exhibited dramatic efficacy in this pediatric patient. This case represents the first successful application of dabrafenib in a pediatric patient with intracranial ECD lesions as well as mixed ECD and LCH. In this article, the authors describe the intricate diagnosis and treatment processes in this patient. Recent studies regarding treatment with BRAF inhibitors for neurological involvement in mixed ECD and LCH are also reviewed.

Langerhans cell histiocytosis mimicking molluscum contagiosum: A case series

Langerhans cell histiocytosis (LCH) is a disorder characterized by accumulation of Langerhans-like cells in one or various organs. A correct staging work-up is essential since there are multiorgan presentations with a poor prognosis. We report three patients with LCH skin lesions mimicking molluscum contagiosum in association with both high and low risk organ involvement. This peculiar cutaneous presentation can be a clue for the diagnosis of LCH, a disease with potentially severe systemic involvement.

A Rare Case of Erdheim-Chester Disease (Non-Langerhans Cell Histiocytosis) with Concurrent Langerhans Cell Histiocytosis: A Diagnostic and Therapeutic Challenge

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocyte disorder most commonly characterized by multifocal osteosclerotic lesions of the long bones demonstrating sheets of foamy histiocyte infiltrates on biopsy with or without histiocytic infiltration of extraskeletal tissues. ECD can be difficult to diagnose since it is a very rare disease that can affect many organ systems. Diagnosis is based on the pathologic evaluation of involved tissue interpreted within the clinical context. Patients who have the BRAF V600E mutation are treated first line with vemurafenib. For those without the mutation with symptomatic ECD, conventional or PEGylated interferon alpha is recommended. For patients who are either intolerant or nonresponsive to interferon alpha, systemic chemotherapy with or without corticosteroids can be used. We present a rare case of Erdheim-Chester disease with concurrent Langerhans cell histiocytosis which occurs in only one fifth of the cases and often presents as a diagnostic and therapeutic challenge.

Differential diagnoses of diaper dermatitis

Diaper dermatitis is the most common contact eczema present in early childhood. The main cause is an irritant reaction to urine and feces, which is facilitated by the occlusive conditions under the diaper, leading to hyperhydration of the stratum corneum (diaper dermatitis). In addition, diaper pressure and friction can increase the risk of skin inflammation, which also opens the skin up to other irritant agents, allergens, and infectious agents, such as candida albicans. However, a variety of diseases are associated with inflammation of the skin in the diaper region, therefore the term "diaper dermatitis" is merely descriptive and does not reflect anything about the etiopathogenesis. The term diaper dermatitis refers only to an inflammation in the diapering area and should not be automatically equated with reactions to diapers. Making the correct diagnosis requires a thorough examination of the skin in its entirety and a detailed report of the patient's medical and family history. Once a specific pattern is identified, a precise diagnosis, and an appropriate therapy, can be determined.

Clinical implications of oncogenic mutations in pulmonary Langerhans cell histiocytosis

PURPOSE OF REVIEW

Langerhans cell histiocytosis (LCH) is a neoplasm of dendritic cells with a wide clinical spectrum. Localized pulmonary LCH occurs in young adults with a history of smoking and can either resolve spontaneously or lead to progressive decline in pulmonary function. Young children can also present with localized disease - frequently bone or skin - or with multifocal or multisystem disease. Clinical outcomes in these patients also vary widely, ranging from spontaneous resolution to multiorgan failure and death. This review describes recent developments in our understanding of the underlying pathogenesis of LCH and how these discoveries and other research are affecting how the disease is classified, treated and monitored.

RECENT FINDINGS

Somatic mutations resulting in activation of the mitogen-activated protein kinase (MAPK) pathway were recently identified as a key pathogenetic mechanism in both pediatric and pulmonary LCH.

SUMMARY

Knowledge of underlying pathogenetic mechanisms of LCH transforming how this disease and other histocytic/dendritic disorders are classified, treated and monitored.

Development of pulmonary Langerhans cell histiocytosis in a patient with established adenocarcinoma of the lung

Newly-appearing lung nodules on surveillance imaging in patients with pre-existing lung cancer can present a diagnostic dilemma when attempting to differentiate between metastatic disease, infection, and other inflammatory conditions. Here we report a case of an EGFR-/ALK-/BRAF+ metastatic adenocarcinoma patient who underwent lung biopsy for evaluation of upper-lobe predominant lung nodules revealed to represent pulmonary Langerhans cell histiocytosis (PLCH). The patient was a heavy smoker and admitted to increase her smoking habit after initially learning about her diagnosis with lung cancer. Interestingly, despite the association of both lung adenocarcinoma and PLCH with the BRAF^V600E mutation in smokers, pyrosequencing of the patient's PLCH lesions was negative for this mutation. Co-occurrence of PLCH with lung cancer is extremely rare. While most reported cases of PLCH tend to precede the occurrence of lung cancer, a minority of cases appear after a diagnosis of lung cancer has already been established and are thought to represent a local immunologic reaction to the tumor. It is therefore postulated that the appearance of PLCH lesions in this patient's lungs is a result of her increase in cigarette smoking, possibly augmented by co-existence of adenocarcinoma.

CNS Erdheim-Chester Disease: A Challenge to Diagnose

Erdheim-Chester disease (ECD) is a rare nonLangerhans cell histiocytosis. Although approximately 50% of cases eventually involve the central nervous system (CNS), the CNS has seldom been reported as the initial biopsy site. The diagnosis of CNS ECD can be challenging due to morphologic overlap with reactive histiocytic proliferation, Langerhans cell histiocytosis (LCH), and extranodal Rosai-Dorfman disease (RDD). We present 3 cases from our files that illustrate the protean manifestations of ECD. Case 1 was a 47-year-old man with ataxia, dysarthria, and intermittent ophthalmoplegia whose cerebellar biopsy had shown only profuse, nonspecific Rosenthal fiber-rich piloid gliosis; ECD was diagnosed only at autopsy. The gliosis and marked variations in histiocyte morphology in different anatomical sites added to the diagnostic challenge. Case 2 was a 67-year-old female with chronic progressive symptoms and a pontine lesion that had been considered to be CLIPPERS by neuroimaging. Identification of a BRAFV600E mutation allowed an ECD diagnosis and treatment with the specific BRAFV600E inhibitor vemurafenib, which resulted in a marked sustained clinical response. Case 3 was diagnosed as ECD after positive bone biopsy with typical foamy histiocytes. Six years later, there was massive dural involvement that showed RDD-like, BRAF-mutation-negative histiocytosis. These cases highlight the clinical and histologic overlap that can occur among these disorders.

Intracranial Erdheim-Chester Disease Mimicking Parafalcine Meningioma: Report of Two Cases and Review of the Literature

BACKGROUND

Erdheim-Chester disease (ECD) is a rare, non-Langerhans cell histiocytosis that typically occurs in middle-aged patients. It is usually characterized by multifocal osteosclerotic lesions of the long-bones, however many cases have extraskeletal involvement. Central nervous system (CNS) involvement is common, but isolated CNS involvement at presentation has rarely been reported.

CASE DESCRIPTION

Here we report two cases of dural-based ECD mimicking meningioma on imaging with no other identified sites of disease.

CONCLUSION

ECD is a rare disease, with isolated CNS involvement reported only a few times in the literature. The significance of this presentation requires additional study and long-term follow up.