A subset of Rosai-Dorfman disease cases show increased IgG4-positive plasma cells: another red herring or a true association with IgG4-related disease?

Pathologic characteristics of histiocytic and dendritic cell neoplasms

Histiocytic and dendritic cell neoplasms comprise diverse tumors originating from the mononuclear phagocytic system, which includes monocytes, macrophages, and dendritic cells. The 5th edition of the World Health Organization (WHO) classification updating the categorization of these tumors, reflecting a deeper understanding of their pathogenesis.In this updated classification system, tumors are categorized as Langerhans cell and other dendritic cell neoplasms, histiocyte/macrophage neoplasms, and plasmacytoid dendritic cell neoplasms. Follicular dendritic cell neoplasms are classified as mesenchymal dendritic cell neoplasms within the stroma-derived neoplasms of lymphoid tissues.Each subtype of histiocytic and dendritic cell neoplasms exhibits distinct morphological characteristics. They also show a characteristic immunophenotypic profile marked by various markers such as CD1a, CD207/langerin, S100, CD68, CD163, CD4, CD123, CD21, CD23, CD35, and ALK, and hematolymphoid markers such as CD45 and CD43. In situ hybridization for EBV-encoded small RNA (EBER) identifies a particular subtype. Immunoprofiling plays a critical role in determining the cell of origin and identifying the specific subtype of tumors. There are frequent genomic alterations in these neoplasms, especially in the mitogen-activated protein kinase pathway, including BRAF (notably BRAF V600E), MAP2K1, KRAS, and NRAS mutations, and ALK gene translocation.This review aims to offer a comprehensive and updated overview of histiocytic and dendritic cell neoplasms, focusing on their ontogeny, morphological aspects, immunophenotypic profiles, and molecular genetics. This comprehensive approach is essential for accurately differentiating and classifying neoplasms according to the updated WHO classification.

Recurrent Soft Tissue Rosai Dorfman Disease of Right Medial Thigh Lipoma With Lymph Node Involvement

Background

Rosai Dorfman disease is a rare non-Langerhans cell histiocytosis that affects lymph nodes, soft tissues, and other organs. The etiology of Rosai Dorfman disease is poorly understood, though it may involve an immunologic processes or infection. Treatment varies according to the disease presentation.

Case Presentation

A male aged 56 years was evaluated for a cutaneous mass on his right medial thigh. Initially, the patient received surgical debulking with subsequent observation and no systemic therapy. However, the mass recurred, prompting another surgical removal 9 years after the initial surgery. A mass biopsy showed infiltration of plasma cells, lymphocytes, histiocytes, and occasional neutrophils with noted reactivity of S-100 protein and CD163, but not CD1a. No systemic therapy was initiated, and the patient agreed to a period of watchful waiting.

Conclusions

Rosai Dorfman disease of soft tissue occurs in older adults and is often associated with soft tissue abnormalities, and more rarely, in lipomas. Multidisciplinary management of the disease and research for mutations and microenvironment of RDD is needed to better understand its clinicopathological nature and improve novel therapies.

IgG4-related lymphadenopathy

IgG4-related lymphadenopathy is a nodal manifestation of IgG4-related disease (IgG4RD) which is characterized by increased polytypic IgG4+ plasma cells and IgG4+/IgG+ plasma cell ratio in lymph nodes and morphologically manifested as various patterns of reactive lymphadenopathy: Castleman disease-like, follicular hyperplasia, interfollicular expansion, progressive transformation of germinal centers and inflammatory pseudotumor-like. It typically presents with solitary or multiple, mild to moderate lymph node enlargement in otherwise asymptomatic patients. The serum IgG4 level is frequently elevated but C-reactive protein often remains normal. In patients not having a history of IgG4RD or manifestation of extranodal IgG4RD, a diagnosis of IgG4-lymphadenopathy should only be made with great caution given the non-specific morphologic features that can overlap with ANCA-associated vasculitis, interleukin-6 syndromes, Rosai-Dorfman disease, inflammatory myofibroblastic tumor, syphilis, lymphoma, and plasma cell neoplasia. Elevated IgG4 parameters, appropriate morphologies, and clinical correlation are essential to make the diagnosis of IgG4-lymphadenopathy more specific and clinically meaningful.

Increased IgG4+ plasma cells are common in excised lymph nodes from children and adolescents without IgG4-related disease

Lymphadenopathy is a common finding in patients with IgG4-related disease (IgG4-RD) and often associated with increased IgG4+ plasma cells in this setting. The histologic features of so-called IgG4-related lymphadenopathy (IgG4-LAD) have seldom been investigated in children and adolescents, and step-wise progression to extranodal IgG4-RD has not been described. This study was performed to further evaluate the frequency, pathologic features, and clinical significance of IgG4-LAD-like histologic changes in the pediatric setting. We analyzed 37 benign lymph nodes collected semi-consecutively from children aged 0-18 years at our institution for both absolute and relative IgG4+ plasma cell abundance and recurrent histomorphologic patterns associated with IgG4-LAD. The combination of IgG4+/IgG+ plasma cell ratio >40% and IgG4+ plasma cell count ≥50 were considered as IgG4-LAD-like per expert consensus guidelines. Seven cases (19%) met both diagnostic criteria. The dominant histomorphologic patterns were follicular hyperplasia (n = 6), interfollicular expansion (n = 3), and progressive transformation of germinal centers (n = 3). Extranodal manifestations of IgG4-RD were not identified in this cohort (38 months average follow-up). Instead, clinical and laboratory findings indicated that lymph node enlargement in most patients could likely be attributed to alternative processes including antecedent dentistry, concurrent infection, and incipient Crohn's disease. Our findings suggest that the histologic features of IgG4-LAD are likely much more common in children and adolescents than previously recognized, often existing in complex with common reactive lymphadenopathies. The diagnostic value of routine immunohistochemical assessment for IgG4+ plasma cells in benign lymph nodes from pediatric patients without established extranodal IgG4-RD and/or other supportive clinical and laboratory data is therefore uncertain.

Cerebral manifestation and diagnostic dilemma of Rosai-Dorfman disease

Rosai-Dorfman disease (RDD) is a rare, S100-positive histiocytic proliferation, that can cause both nodal and extranodal illness. We present a case of a 53-year-old male patient. Magnetic resonance imaging described a plaque-like meningeal lesion, and the preoperative diagnosis was meningioma. Histologically, dense infiltration of lymphocytes, plasma cells, and histiocytes was seen, furthermore, the presence of emperipolesis in the sample was pronounced. In the histiocytes nuclear and cytoplasmic positivity with S100 protein, and nuclear positivity with Cyclin D1 was observed. The case was concluded as RDD. Morphological appearance of intracranial RDD with imaging procedures can present a differential diagnostic challenge. The correct diagnosis is based on the presence of histiocytes with emperipolesis, and properly defined immunohistochemical characteristics.

The evaluation of IgG4 and IgG expression in cutaneous Rosai-Dorfman disease

OBJECTIVE

The authors investigated the expression of IgG4 and IgG in cutaneous Rosai-Dorfman Disease (CRDD) to further improve the understanding of this disease.

METHODS

The authors retrospectively reviewed the clinicopathological features of 23 CRDD patients. The authors diagnosed CRDD by the presence of emperipolesis and immunohistochemical (IHC) staining of histiocytes consisting of S-100(+)/CD68(+)/CD1a(-) cells. The expressions of IgG and IgG4 in cutaneous specimens were assessed by IHC (EnVision) and quantitatively calculated by a medical image analysis system.

RESULTS

All 23 patients, including 14 males and 9 females, were confirmed to have CRDD. Their ages ranged from 17 to 68 years (mean 47.91 ± 14.16). The most frequently affected skin regions were the face, followed by the trunk, ears, neck, limbs, and genitals. In 16 of these cases, the disease presented as a single lesion. IHC staining of sections showed that IgG was positive (≥ 10 cells/High-Power Field [HPF]) in 22 cases, while IgG4 was positive (≥ 10 cells/HPF) in 18 cases. Moreover, the IgG4/IgG proportion ranged from 1.7% to 85.7% (mean 29.50 ± 24.67%, median 18.4%) in the 18 cases.

STUDY LIMITATIONS

In the majority of studies, as well as in the current study, the design. RDD is a rare disease, so the sample size is small. In the next studies to come, the authors will expand the sample for multi-center verification and in-depth study.

CONCLUSION

The positive rates of IgG4 and IgG and the IgG4/IgG ratio assessed through IHC staining may be important in understanding the pathogenesis of CRDD.

Rosai-Dorfman-Destombes Disease in the Pediatric Head and Neck

BACKGROUND

Rosai-Dorfman-Destombes disease (RDD), or sinus histiocytosis with massive lymphadenopathy, is a rare form of non-Langerhans cells histiocytosis. It has a wide-ranging variability in presentation since first described in 1969 but much of its characteristics in children remain unknown.

METHODS

A retrospective chart review of children diagnosed with RDD at a tertiary care children's hospital was conducted from 2000 to 2021.

RESULTS

Twelve RDD patients were identified, with an average age of 7 years (SD 4.3). Males comprised 58% of the cohort, and African American ethnicity was most common (42%). Nodal RDD was found in 7 patients (58%). Nine patients (75%) presented RDD within the head and neck, 6 of whom had nodal RDD. The most common presentation was cervical lymphadenopathy, which most often involved levels V (67%), II (56%), III (44%), and I (11%), in order of frequency. Recurrence and persistence of disease after initial treatment was common, with 5 (42%) being disease free at the time of the last follow up. Fifty-eight percent (7/12) developed recurrence or had persistent disease and 4 required adjuvant systemic treatment with corticosteroids and/or chemotherapy. One patient succumbed after developing treatment related acute myelodysplastic leukemia (t-AML) from chemotherapy used to treat recurrent RDD.

CONCLUSION

Pediatric RDD presents at a young age and most commonly involving cervical lymphadenopathy. Ongoing surveillance in the setting of persistence or recurrence without clearly defined prognostic risk factors is important.

Rosai-Dorfman Disease in the Skull Base: A Case Series Study

OBJECTIVE

Rosai-Dorfman disease (RDD) is a rare, idiopathic, and non-neoplastic histio-proliferative disease that is uncommon in the central nervous system. Hence, reports of management of RDD in the skull base are scarce and only a few studies on skull base RDD are available. The objective of this study was to analyze the diagnosis, treatment, and prognosis of RDD in the skull base and explore an appropriate treatment strategy thereof.

METHODS

Nine patients with clinical characteristics and follow-up data from our department between 2017 and 2022 were included in this study. From this information, the clinical profiles, imaging, treatment, and prognosis data were collected.

RESULTS

There were 6 male and 3 female patients with skull base RDD. These patients ranged in age from 13 to 61 years, with a median age of 41 years. The locations included 1 anterior skull base orbital apex, 1 parasellar region, 2 sellar regions, 1 petroclivus, and 4 foramen magnum regions. Six patients underwent total resection and 3 underwent subtotal resection. Patient follow-up lasted 11-65 months, with a median duration of 24 months. One patient died, 2 experienced recurrence, and the other patients' lesions were stable. The symptoms worsened and new complications occurred in 5 patients.

CONCLUSIONS

Skull base RDDs are intractable diseases with a high rate of complications. Some patients are at risk of recurrence and death. Surgery may be the basic treatment for this disease, and combined therapy including targeted therapy or radiation therapy may also be a valuable therapeutic strategy.

Immunoglobulin G4-Associated Rosai-Dorfman Disease: Report of 3 Cases

Rosai-Dorfman disease is characterized by dilated lymph node sinuses filled with lymphocytes, plasma cells, and histiocytes. Many of these histiocytes classically exhibit emperipolesis of lymphocytes and plasma cells. Abundant immunoglobulin G4+ plasma cells occur in some cases, and a potential relationship with immunoglobulin G4-related disease has been suggested. Here, we report 3 cases of immunoglobulin G4-associated Rosai-Dorfman disease. Immunoglobulin G4-related disease was suspected based on immunoglobulin G4+ plasma cell infiltration, but the final diagnosis was immunoglobulin G4-associated Rosai-Dorfman disease. At present, the evidence does not support a link between immunoglobulin G4-associated Rosai-Dorfman disease and immunoglobulin G4-related disease, and one condition should not be considered part of the spectrum of the other. We believe it is of paramount importance to increase the awareness of immunoglobulin G4-associated Rosai-Dorfman disease for pathologists who interpret the biopsies and clinicians who integrate the diagnosis and treat such patients to not overdiagnose immunoglobulin G4-related disease.

Recent advances in IgG4-related kidney disease

Recent advances in the management and understanding of immunoglobulin (Ig)G4-related kidney disease (RKD) have emphasized the importance of urgent treatment in IgG4-related tubulointerstitial nephritis. On the other hand, to avoid long-term glucocorticoid toxicity, strategies for early withdrawal of steroids or combination of immunosuppressants, such as rituximab, and the minimum dose of steroids have been pursued. However, disease recurrence after reducing or stopping steroid therapy hampers early withdrawal of glucocorticoid maintenance therapy. In addition, knowledge has accumulated in diagnostic approaches including differential diagnosis of anti-neutrophil cytoplasmic antibodies-associated vasculitis, idiopathic multicentric Castleman's disease, and Rosai-Dorfman disease with kidney lesion, which leads to earlier and precise diagnosis of IgG4-RKD. This review summarizes recent progress in the differential diagnosis of IgG4-RKD and related treatment strategies and recent topics of hypocomplementaemia, membranous glomerulonephritis, and IgG4-related pyelitis and periureteral lesion.

Immunoglobulin G4-Related Disease, Lymphadenopathy, and Lymphoma

Lymphadenopathy occurring in patients with immunoglobulin G4 (IgG4)-related disease, termed IgG4-related lymphadenopathy, shows morphologic heterogeneity and overlap with other nonspecific causes of lymphadenopathy including infections, immune-related disorders, and neoplasms. This review describes the characteristic histopathologic features and diagnostic approach to IgG4-related disease and IgG4-related lymphadenopathy, with comparison to nonspecific causes of increased IgG4-positive plasma cells in lymph nodes, and with emphasis on distinction from IgG4-expressing lymphoproliferative disorders.

Development of IgG4-related pancreatitis and kidney disease 7 years after the onset of undiagnosed lymphadenopathy: A case report

This report describes a patient diagnosed with immunoglobulin G4 (IgG4)-related pancreatitis and kidney disease 7 years after the onset of undiagnosed lymphadenopathy. A 48-year-old Japanese woman presented with fatigue and leg oedema. Computed tomography showed perigastric lymphadenopathy, for which she underwent a laparoscopic biopsy of the perigastric lymph nodes. Although histopathological examination of the lymph nodes did not lead to a definitive diagnosis, serological tests revealed elevated serum IgG4 levels (558 mg/dl) and IgG4 immunostaining of the lymph nodes showed IgG4-positive plasma cell infiltration, leading to the suspicion of IgG4-related disease. Further workup revealed no organ lesion other than lymphadenopathy. At age 55 years, despite having no subjective symptoms, contrast-enhanced computed tomography showed low-density lesions in the tail of the pancreas and the left kidney. Histopathological examination showed lymphocyte infiltration, consisting of a mixture of plasma cells and eosinophils, in both organs and obliterative phlebitis in the pancreas. IgG4 immunostaining of the kidney specimens showed 160 IgG4-positive cells per high-powered field, with the IgG4+/IgG+ cell ratio being almost 100%, leading to a diagnosis of IgG4-related pancreatitis and kidney disease. Treatment with prednisolone for 2 months resulted in lesion improvement. Although the diagnosis of IgG4-related lymphadenopathy is often challenging in patients with lymphadenopathy alone, findings in the present patient emphasise the importance of long-term follow-up, as it may allow early detection of involvement of other organs by IgG4-related disease.

A report of Rosai-Dorfman disease with systemic multiple lymphadenopathy and high IgG4 plasma cell infiltration

The Rosai-Dorfman disease (RDD) is a kind of sinus histiocytosis with massive lymphadenopathy and is remarkably rare. RDD is characterized by large histiocytes with emperipolesis. However, the cause of RDD is unknown, and most cases are relieved spontaneously. In rare cases, patients may have onset and remission of lymph nodes and extranodal involvement. This report showed an RDD case in a 67-year-old male patient with systemic superficial lymphadenopathy and high IgG4 plasma cell infiltration. We showed that a possible RDD diagnosis should be kept in mind when encountering a systemic multiple lymphadenopathy and high IgG4 plasma cell infiltration. Also, an overlap between RDD and IgG4-related disease might be present, which might help in clinical recognition of RDD.

Rosai-Dorfman Disease between Proliferation and Neoplasia

Rosai-Dorfman disease (RDD) is a rare myeloproliferative disorder of histiocytes with a broad spectrum of clinical manifestations and peculiar morphologic features (accumulation of histiocytes with emperipolesis). Typically, the patient with RDD shows bilateral painless, massive cervical lymphadenopathy associated with B symptoms. Approximately 43% of patients presented with extranodal involvement. According to the 2016 revised histiocytosis classification, RDD belongs to the R group, including familial and sporadic form (classical nodal, extranodal, unclassified, or RDD associated with neoplasia or immune disease). Sporadic RDD is often self-limited. Most RDD needs only local therapies. Nevertheless, a small subpopulation of patients may be refractory to conventional therapy and die of the disease. Recent studies consider RDD a clonal neoplastic process, as approximately 1/3 of these patients harbor gene mutations involving the MAPK/ERK pathway, e.g., NRAS, KRAS, MAP2K1, and, rarely, the BRAF mutation. In addition to typical histiocytic markers (S100/fascin/CD68/CD163, etc.), recent studies show that the histiocytes in RDD also express BCL-1 and OCT2, which might be important in pathogenesis. Additionally, the heterozygous germline mutation involving the FAS gene TNFRSF6 is identified in some RDD patients with an autoimmune lymphoproliferative syndrome type Ia. SLC29A3 germline mutation is associated with familial or Faisalabad histiocytosis and H syndrome.

A unique case of isolated thoracic spinal Rosai-Dorfman disease related to IgG4

Rosai-Dorfman disease (RDD) is a rare benign histiocytosis usually characterized by massive cervical lymphadenopathy and systemic manifestations. Extranodal, especially spinal involvement, is extremely rare. Our case was deemed worthy of presentation because it was the first reported isolated case of spinal RDD related to IgG4 and mimicked meningioma clinically and radiologically. A case with an intradural extramedullary mass causing neurological compression findings in the thoracic spinal region and radiologically mimicking meningioma is presented. In the histomorphological examination of the resection material, polymorphonuclear leukocytes in the dura, histiocytes showing emperipolesis, an increase in collagenized fibrous connective tissue, and intense lymphoplasmacytic cell infiltration accompanied by obliterative phlebitis were observed. Immunohistochemically, the histiocytic cells were found to be S-100 protein, CD68, and CD163 positive and CD1a and langerin negative, and more than half of the plasma cells were immunoglobulin-G4 (IgG4) positive. Although rare, RDD or IgG4-related meningeal disease should be considered in the differential diagnosis of dural-based spinal masses that radiologically suggest meningioma. The pathologist should be aware that these two histopathological entities may coexist. To our knowledge, this is the first case of "isolated spinal RDD related to IgG4" reported in the literature.

Histiocytic Disorders of Childhood

Histiocytic disorders of childhood represent a wide spectrum of conditions that share the common histologic feature of activated or transformed "histiocytes." Langerhans cell histiocytosis (LCH) is the most common, with an incidence of approximately 5 per million children. LCH may be difficult to distinguish from more ubiquitous causes of skin rashes, bone pain, or fever. Current chemotherapy fails to cure more than 50% of children with multifocal disease, and treatment failure is associated with increased risks of long-term sequelae. Somatic activating mitogen-activated protein kinase (MAPK) pathway-activating mutations (most often BRAFV600E) have been identified in hematopoietic precursors in patients with LCH. Opportunities to improve outcomes with targeted therapies are under investigation. Juvenile xanthogranuloma (JXG) and Rosai-Dorfman disease (RDD) are less common than LCH and are distinguished by specific histologic and clinical features. Recurrent MAPK pathway gene mutations are also identified in JXG and RDD. In many cases, these conditions spontaneously resolve, but disseminated disease can be fatal. Although there has been historic debate regarding the nature of these conditions as inflammatory versus neoplastic, LCH, JXG, and RDD are now considered myeloid neoplastic disorders. In contrast, hemophagocytic lymphohistiocytosis (HLH) is clearly a disorder of immune dysregulation. HLH is characterized by extreme immune activation driven by hyperactivated T cells. HLH arises in approximately 1 child per million and is nearly universally fatal without prompt recognition and immune suppression. Outcomes of treated children are poor, with approximately 60% survival. Emapalumab, which targets interferon-γ signaling, was recently approved for patients with recurrent or refractory HLH, and additional cytokine-directed therapies are under investigation.

Rosai-Dorfman Disease Presenting as Massive Mediastinal Lymphadenopathy in an Elderly Man

We present a patient case of a 73-year-old man with new-onset substernal chest pain and B symptoms, found on computed tomography imaging to have massive mediastinal lymphadenopathy of more than 6 cm. Positron emission tomography imaging revealed fluorodeoxyglucose-avid nodes further extending to the axillary, abdominal, and inguinal regions. After a broad patient work-up for infectious, malignant, and rheumatic causes, he was ultimately diagnosed with Rosai-Dorfman disease, a rare histiocytic neoplasm, by excisional lymph node biopsy.

Report of Two Cases of Pediatric IgG4-Related Lymphadenopathy (IgG4-LAD): IgG4-Related Disease (IgG4-RD) or a Distinct Clinical Pathological Entity?

IgG4-related disease (IgG4-RD) is a recently discovered immune-mediated fibroinflammatory condition, uncommon in the pediatric population, that could involve multiple organs and induce cancer-like lesions and organ damage. Its main features are multiple injuries in different sites, a dense lymphoplasmacytic infiltrate rich in IgG4 plasma cells, storiform fibrosis, and often high serological concentrations of IgG4. Autoimmune pancreatitis is the most common manifestation, mainly in adults. Two cases of IgG4-RD in children with lymph node localization of disease are reported. Localized or systemic lymph node involvement is common, but lymph node enlargement as the first and only manifestation of IgG4-RD is unusual, and therefore, hard to differentiate from other diseases. IgG4-related lymphadenopathy (IgG4-LAD) is most likely a distinct disease, described as isolated lymphadenopathy, related to the presence of elevated numbers of IgG4-positive plasma cells. Both disorders are likely to be misdiagnosed in children because they are characterized by rare and polymorphic features. IgG4-RD and IgG4-LAD should be considered in the differential diagnosis of disorders characterized by lymphadenopathy of uncertain etiology.

Rosai-Dorfman Disease With Features of IgG4-Related Sclerosing Disease: A Case Report

Rosai-Dorfman disease (RDD) is a rare condition characterized by the proliferation of non-Langerhans cell histiocytes that are associated with phagocytosed lymphocytes (emperipolesis). Clinically, it is classified into nodal, extra-nodal, neoplasia-associated RDD, and immune-related. Here, we present a case of a 65-year-old female who presented with facial pain following a dental procedure with no focal neurologic deficit. The MRI of the head and neck showed a well-defined lobulated soft tissue lesion with homogenous enhancement over the left cheek. Excision of the lesion was done, and the histopathological study reported extra-nodal RDD with features of IgG4-related sclerosing disease. The patient had no recurrence over the two years from the date of diagnosis.

IgG4-Related Disease: Mimickers and Diagnostic Pitfalls

BACKGROUND

The tendency of IgG4-related disease (IgG4-RD) to form pseudotumors, as well as its multisystemic nature, makes it the perfect mimicker of many conditions. Moreover, some clinical, serological, radiological, or histological features of the disease might be shared with some mimickers.Recently, 4 clinical phenotypes have been identified, and patients grouped in each phenotype have distinctive demographic, clinical, and serological features and outcomes, and, as expected, for each phenotype, a set of differential diagnoses should be considered.

SUMMARY OF THE LITERATURE

The main differential diagnoses for the pancreato-hepato-biliary phenotype are pancreatic adenocarcinoma and cholangiocarcinoma. Other differential diagnoses include type 2 autoimmune pancreatitis and primary sclerosing cholangitis. In patients with retroperitoneal/aortic phenotype, inflammatory conditions such as idiopathic retroperitoneal fibrosis and large vessel vasculitides should be ruled out, and most of the time, a biopsy will be needed to exclude malignancies. In head and neck limited phenotype, autoimmune conditions (eg, granulomatosis with polyangiitis, Graves orbitopathy, sarcoidosis), malignancies, and histiocytosis should be ruled out, whereas the main differential diagnoses of the Mikulicz/systemic phenotype are Sjögren syndrome, granulomatosis with polyangiitis, and multicentric Castleman disease.

CONCLUSIONS

Approaching a patient with probable IgG4-RD through a clinical phenotype framework will ease the diagnostic algorithm and facilitate the prompt recognition of the disease. There are certain clinical, serological, radiological, and histological features in each clinical phenotype that, if present, increase the likelihood that a patient may have IgG4-RD instead of the mimicker condition. Those clues that point toward IgG4-RD diagnosis should be actively sought in the workup of patients.

Rosai-Dorfman Disease of Bone and Soft Tissue

Context.—

Rosai-Dorfman disease is a rare histiocytic proliferative disorder of unknown pathogenesis that may be diagnostically difficult in extranodal sites. It is commonly an unsuspected diagnosis when arising in bone and soft tissue, especially when it presents without associated lymphadenopathy. Its variable clinical presentation and nonspecific imaging findings make the diagnosis quite challenging, particularly in small biopsies. The problem is compounded by its less-characteristic histomorphologic features in comparison with nodal disease. Awareness of the potential diagnostic pitfalls in Rosai-Dorfman disease of bone and soft tissue should raise the degree of diagnostic accuracy.

Objective.—

To review the clinical manifestations, imaging characteristics, and histomorphologic features of Rosai-Dorfman disease of bone and soft tissue along with a brief discussion of its differential diagnosis, pathogenesis, and current management.

Data Sources.—

Thorough review of the literature with focus on clinical manifestations, imaging findings, key histomorphologic features, pathogenesis, and treatment.

Conclusions.—

The diagnosis of Rosai-Dorfman disease of bone and soft tissue may be quite challenging because of its variable clinical presentation and nonspecific imaging findings. It may be asymptomatic without systemic manifestations or associated lymphadenopathy. The definitive diagnosis relies on histopathologic identification of the characteristic S-100–positive histiocytes demonstrating emperipolesis. Bone and soft tissue lesions tend to have lower numbers of characteristic histiocytes and less conspicuous emperipolesis and often demonstrate areas of fibrosis or storiform spindle cell areas resembling fibrohistiocytic lesions. Awareness of these unusual features is necessary in order to consider Rosai-Dorfman disease in the differential diagnosis when confronting these rare and often misleading lesions.

Rosai-Dorfman disease. A legacy of Professor Rosai that is still not exploited completely

Rosai-Dorfman disease (RDD) is a rare form of non-Langerhans cell histiocytosis described by Rosai and Dorfman in 1969. It is a fascinating disease characterized by accumulation of large, pale histiocytes, frequently showing the emperipolesis phenomenon. The variety of pathological aspects and the spectrum of different clinical forms were deeply investigated by Prof. Rosai. Despite recent advancements in the dissection of pathogenetic mechanisms of RDD, with the identification of gene mutations in the MAP kinase pathway, several biological and clinical aspects of this disease remains to be elucidated: this is one of the Prof. Rosai's legacies.

Histiocytosis

Histiocytoses constitute a heterogeneous group of rare disorders, characterised by infiltration of almost any organ by myeloid cells with diverse macrophage or dendritic cell phenotypes. Histiocytoses can start at any age. Diagnosis is based on histology in combination with appropriate clinical and radiological findings. The low incidence and broad spectrum of clinical manifestations often leads to diagnostic delay, especially for adults. In most cases, biopsy specimens infiltrated by histiocytes have somatic mutations in genes activating the MAP kinase cell-signalling pathway. These mutations might also be present in blood cells and haematopoietic progenitors of patients with multisystem disease. A comprehensive range of investigations and molecular typing are essential to accurately predict prognosis, which can vary from spontaneous resolution to life-threatening disseminated disease. Targeted therapies with BRAF or MEK inhibitors have revolutionised salvage treatment. However, the type and duration of treatment are still debated, and the prevention of neurological sequelae remains a crucial issue.

Rosai-Dorfman-Destombes (RDD) disease presenting as palindromic rheumatism

Background

Rosai-Dorfman-Destombes (RDD) disease, is a rare proliferative and inflammatory disorder of non-Langerhans cell histiocytes.

Case presentation

We report a 35-year-old woman, who originally presented with recurrent episodes of lower extremity joint/bone pain and chronic nasal stuffiness and congestion. Her worsening nasal congestion was due to an obstructing nasal cavity lesion which was subsequently biopsied. Pathology was consistent with RDD. ¹⁸F-FDG PET images demonstrated intense uptake in the paranasal sinuses and a large pelvic lymph node. Focal osseous lesions with intense ¹⁸F-FDG uptake were also observed in the lower extremity, corresponding to areas of peri-articular pain. Rheumatologic work-up was consistent with palindromic rheumatism. She was diagnosed with immune-related disseminated RDD, presenting as palindromic rheumatism.

Conclusions

This is the first case of RDD presenting as palindromic rheumatism. RDD should be considered as a possible but rare diagnosis in young patients with sinus-related symptoms and lymphadenopathy. The disease can on rare occasions be disseminated and can also present as immune-related RDD, such as in this patient.

IgG4-related Lymphadenopathy: A Comparative Study of 41 Cases Reveals Distinctive Histopathologic Features

Lymphadenopathy is common in patients with immunoglobulin G4-related disease (IgG4-RD). However, the described histopathologic features of IgG4-related lymphadenopathy have been shown to be largely nonspecific. In an attempt to identify features specific for nodal IgG4-RD we examined the histopathologic features of lymph nodes from 41 patients with established IgG4-RD, with comparison to 60 lymph nodes from patients without known or subsequent development of IgG4-RD. An increase in immunoglobulin (Ig) G4-positive plasma cells >100/HPF and IgG4/IgG ratio >40% was identified in 51% of IgG4-RD cases and 20% of control cases. Localization of increased IgG4-positive plasma cells and IgG4/IgG ratio to extrafollicular zones was highly associated with IgG4-RD, particularly when identified in regions of nodal fibrosis (P<0.0001; specificity: 98.3%), or in the context of marked interfollicular expansion (P=0.022; specificity: 100%). Other features characteristic of IgG4-RD included frequent eosinophils associated with IgG4-positive plasma cells, phlebitis (P=0.06), and perifollicular granulomas (P=0.16). The presence of an isolated increase in intrafollicular IgG4-positive plasma cells and IgG4/IgG ratio was more frequently present in control cases than IgG4-RD (P<0.0001). This study confirms that increased IgG4-positive plasma cells and IgG4/IgG ratio are neither sensitive nor specific for the diagnosis of IgG4-related lymphadenopathy, and most described morphologic patterns are nonspecific. In contrast, nodal involvement by IgG4-rich fibrosis akin to extranodal IgG4-RD or diffuse interfollicular expansion by IgG4-positive plasma cells are highly specific features of true IgG4-related lymphadenopathy. Our findings provide for a clinically meaningful approach to the evaluation of lymph nodes that will assist pathologists in distinguishing IgG4-related lymphadenopathy from its mimics.

Pathology of IgG4-related sclerosing mastitis

Immunoglobulin G4-related sclerosing mastitis (IgG4-RM) is a recently recognised member of the IgG4-related disease (IgG4-RD) family, a multisystem fibroinflammatory condition that can affect any organ system. IgG4-RM is rare and predominantly occurs in middle-aged women. It may present with painless palpable mass and/or lymphadenopathy thereby mimicking breast cancer. Although there is an abundance of literature describing the clinicopathological characteristics of IgG4-RD in a variety of organs, data on IgG4-RM are limited due to its rarity. This review describes the manifestation of the disease in the breast based on reported cases, emphasising the clinicopathological features, pathophysiology, differential diagnosis, treatment and prognosis.

Autopsy case of Rosai-Dorfman disease presenting as fibrinous pericarditis

Rosai-Dorfman disease (RDD) is a rare non-Langerhans cell histiocytosis that is characterized histopathologically by accumulation of CD68-positive, S100-positive, and CD1a-negative histiocytes. Cardiac involvement of RDD is rare. We report here an autopsy case of cardiac involvement of RDD presenting as fibrinous pericarditis. A 14-year-old Japanese boy complained of loss of appetite and breathing difficulty when lying down. He was found dead on his back in his bedroom. One year before his death, he was diagnosed with RDD after skin biopsy. At autopsy, the deceased was 153 cm in height and weighed 38 kg with systemic edema. He had flat pigmented light-brown spots, as well as many pale reddish-brown papules on the abdomen and both thighs. Cervical and mediastinal lymphadenopathy was observed. A large amount of pleural and ascitic fluid was observed. The spleen weighed 381.9 g and showed splenomegaly. The heart weighed 620 g and showed acute fibrinous pericarditis with adhesion. Abundant fibrin was observed on the epicardial surface. The infiltrating cells were CD68-positive, S100-positive, and CD1a-negative histiocytes. The skin and spleen showed histiocytic involvement. Systemic edema, large amounts of pleural and ascitic fluid, a high brain natriuretic peptide level in blood, and hemosiderin-laden macrophages in the lungs suggested chronic heart failure. We speculate that the cause of death was extranodal cardiac involvement of RDD with chronic heart failure. This case highlights the need for forensic pathologists to perform a complete autopsy to determine the cause of sudden death when cardiac involvement of RDD is present.

Rosai-Dorfman disease mimicking IgG4-related diseases: a single-center experience in China

Background

Rosai–Dorfman disease (RDD) and IgG4-related (IgG4-RD) disease are both rare diseases, but in some cases, RDD mimics IgG4-RD clinically and pathologically. RDD mimicking IgG4-RDs (RDD mimic IgG4-RD), referring to disease initially diagnosed as IgG4-RD but finally pathologically confirmed to be RDD, is a clinically rare and confusing disease. To summarize the characteristics of this disease, we prospectively analyzed the clinical features, laboratory parameters, pathological characteristics, treatment and prognosis of patients diagnosed with RDD mimic IgG4-RD. Moreover, by analyzing characteristics of RDD mimic IgG4-RD, RDD and IgG4-RD, we further compared the similarities and differences between RDD and IgG4-RD.

Results

7 patients with RDD mimic IgG4-RD were included in this study and all of them had extranodal organ involvement, especially the central nervous system, which occurred in 5 patients (71.4%). Although serum IgG4 level was elevated in 6 cases (1360–54,100 mg/L), overall, it was still lower than that in IgG4-RD patients. Furthermore, we found a new cut-off value of serum IgG4 concentration for differentiating RDD and IgG4-RD with higher specificity. Pathological findings of RDD also showed features resembling IgG4-RD: IgG4-positive plasma cell enrichments were observed in all RDD mimic IgG4-RD patients, and the proportion of IgG4/IgG in tissues was 10–40% in 4 patients and more than 40% in 2 patients. However, none of the RDD mimic IgG4-RD patients or RDD patients displayed obliterative phlebitis or storiform fibrosis. Most of the RDD mimic IgG4-RD patients were treated with glucocorticoids combined with immunosuppressants, and a good prognosis was obtained following treatment.

Conclusions

RDD has clinical manifestations that mimic IgG4-RD. However, detailed differences in laboratory parameters and pathological characteristics are present between these two diseases. Our study underlines the necessity to rule out RDD while diagnosing IgG4-RD using pathological findings as the identification criteria and provides advice for both differentiating these two diseases and clinical treatment of RDD mimic IgG4-RD.

Orbital Rosai-Dorfman disease initially diagnosed as IgG4-related disease: a case report

Inflammatory orbital lesions include a broad list of diagnoses, many of them with overlapping clinical and radiographic features. They often present a diagnostic conundrum, even to the most experienced orbital specialist, thus placing considerable weight on surgical biopsy and histopathological analysis. However, histopathological diagnosis is also inherently challenging due to the rarity of these lesions and the overlaps in histologic appearance among distinct disease entities. We herein present the case of an adolescent male with a subacutely progressive orbital mass that generated a significant diagnostic dilemma. Early orbital biopsy was consistent with a benign fibro-inflammatory lesion, but corticosteroid therapy was ineffective in halting disease progression. After an initial substantial surgical debulking, histopathological analysis revealed several key features consistent with IgG4-related disease (IgG4-RD), a systemic fibro-inflammatory process typically accompanied by multifocal tumor-like lesions. Surprisingly, within months, there was clear evidence of clinical and radiographic disease progression despite second-line rituximab treatment, prompting a second surgical debulking. This final specimen displayed distinctive features of Rosai-Dorfman disease (RDD), a systemic inflammatory disease characterized by uncontrolled histiocytic proliferation. Interestingly, certain features of this re-excision specimen were still reminiscent of IgG4-RD, which not only reflects the difficulty in differentiating RDD from IgG4-RD in select cases, but also illustrates that these diagnoses may exist along a spectrum that likely reflects a common underlying pathogenetic mechanism. This case emphasizes the importance of surgical biopsy or resection and histopathological analysis in diagnosing—and, ultimately, treating—rare, systemic inflammatory diseases involving the orbit, and, furthermore, highlights the shared histopathological features between RDD and IgG4-RD.

Rosai-Dorfman disease: an overview

CONTEXT

Rosai-Dorfman disease is an uncommon histiocytic disorder most frequently presenting as bilateral cervical lymphadenopathy in children and young adults. Extranodal disease occurs in a significant proportion of patients. It has been recently classified as part of the 'R group' of histiocytoses by the Histiocyte Society in 2016. Cutaneous Rosai-Dorfman disease is regarded as a separate disease entity that falls into the 'C group' of histiocytoses according to this classification system. The pathogenesis was previously poorly understood; however, recent evidence demonstrating clonality in a subset of cases raises the possibility of a neoplastic process. A possible association with IgG4-related disease remains controversial.

OBJECTIVES

To provide a comprehensive review of Rosai-Dorfman disease, including nodal, extranodal and cutaneous forms, with a particular emphasis on new insights into the possible clonal nature of the disease; to discuss the recently revised classification of the histiocytoses by the Histiocyte Society; and to summarise the findings from the literature regarding the controversial association with IgG4-related disease.

DATA SOURCES

This review is based on published peer-reviewed English literature.

CONCLUSIONS

Classic Rosai-Dorfman disease, which may be sporadic or familial, is considered a separate entity from cutaneous disease, which is reflected in the revised classification of histiocytoses. An increase in IgG4-positive plasma cells may be seen in Rosai-Dorfman disease. This finding in isolation is of limited significance and should be interpreted with caution. Studies investigating the molecular profile of the disease show that in at least a subset of cases the disease is a clonal process. The classification of Rosai-Dorfman disease is therefore likely to change as our understanding of the aetiopathogenesis evolves.

Intracranial Rosai-Dorfman disease mimicking melanoma: a case report and review of the literature

Intracranial Rosai-Dorfman disease is quite rare. Here, we report a 67-year-old man with a 90 day history of pain and numbness in his right limbs. The patient was suspected of suffering from melanoma. Then he received craniotomy and was finally diagnosed with intracranial Rosai-Dorfman disease. MEDLINE was used to search the related literature; and the diagnosis, mechanism, treatment and prognosis of this rare tumor are discussed.

First Report of IgG4 Related Disease Primary Presenting as Vertebral Bone Marrow Lesions

IgG4-related disease is a fibro-inflammatory disorder characterized by swelling of tissues and affected organs accompanied by the development of scar tissue (fibrosis) and infiltration by IgG4 positive plasma cells. Almost any organ can be affected, including, but rarely, bone marrowinvolvement. Here we present a case of a 76-year-old male with IgG4-related disease presenting primarily with vertebral bone marrow lesions. Histopathology showed the typical features of storiform fibrosis, and increased IgG4 positive plasma cells. Treatment with corticosteroids significantly improved wellbeing and resolved lesion size on MRI.

Large dural-based mass with bony hyperostosis in a 16-year-old male: IgG4-related disease mimicking lymphoplasmacyte-rich meningioma

BACKGROUND

IgG4-related disease is an autoimmune process that presents with tumefactive lesions characterized by storiform fibrosis, a dense lymphoplasmacytic infiltrate rich in IgG4+ plasma cells, obliterative phlebitis, and often elevated serum IgG4 levels. Central nervous system IgG4-related disease is very rare and usually occurs in the form of hypertrophic pachymeningitis or hypophysitis. Presentation as a large solitary meningioma-like mass with overlying hyperostosis in a young adult has not been reported before.

CASE SUMMARY

A 16-year-old male presented with focal seizures for 5 months. Imaging showed a large, extra-axial, and contrast-enhancing mass lesion in the left frontoparietal region with focal calvarial thickening. Histopathology revealed a fibrosclerotic lesion involving dura with a polymorphic infiltrate of plasma cells, mature lymphocytes, histiocytes, and occasional eosinophils. Immunohistochemical workup excluded the possibilities of meningioma, lymphoproliferative neoplasms, and histiocytic lesions. Majority of plasma cells were IgG4+ rendering a diagnosis of IgG4-related disease. Further serological and imaging workup did not reveal any evidence of systemic involvement. His serum IgG4 levels were normal. Considering a gross total resection of the lesion, no further treatment was given and the patient has been asymptomatic since.

CONCLUSION

IgG4-related lesions of the CNS are under-recognized and accurate diagnosis, especially in those with isolated CNS disease and normal serum IgG4 levels, necessitates robust histopathological and laboratory workup to exclude mimics. They may occur as large dural masses with hyperostosis and differentiation from lymphoplasmacyte-rich meningiomas, in particular, can be challenging. While steroids are the mainstay of treatment in IgG4-related disease, surgical resection may be curative in solitary lesions presenting with compressive symptoms.

Extra Nodal Rosai-Dorfman Disease Originating in the Nasal and Paranasal Complex and Gnathic Bones: A Systematic Analysis of Seven Cases and Review of Literature

Rosai-Dorfman disease (RDD) is a benign, self-limiting histiocytosis of unknown etiology. The classic form of the condition includes a painless cervical lymphaenopathy accompanied by fever, weight loss and an elevated ESR. Extra nodal RDD (ENRDD) is most frequent in the head and neck. Thirty-eight cases of ENRDD have been described. Seven cases of ENRDD were identified in our pathology biopsy services. The demographic and clinical information was tabulated logically on the basis of age, gender, location and presence or absence of symptoms, treatment and follow-up. Radiographic and histopathological features were also examined. The findings in these cases were correlated with those available from the previously reported cases. Six cases affected women and one case was diagnosed in a male. The age ranged from 22-55 years. Three cases presented as a nasal mass. One of these lesions extended into the paranasal sinuses. One case was located in the maxilla and extended to involve the maxillary sinus. Three cases were diagnosed in the mandible. The maxillary and one mandibular lesion (Case 2) resulted in significant painful irregular bone destruction with a non-healing socket and tooth mobility respectively. One mandibular lesion was asymptomatic (Case 6). The third case affecting the mandible presented as a rapidly expansile mass following a tooth extraction (Case 7). Nasal masses presented with symptoms of obstruction. Nasal masses were excised with no recurrence from up to 2-3 years of follow-up. The mandibular lesions were curetted aggressively. The oral mass in Case 7 was excised synchronously. No recurrence up to 2 years was recorded in Case 2. Follow-up information is not available for Cases 6 and 7. The maxillary lesion was not intervened surgically. The patient has persistent but stable disease for a follow-up period of 2 years. ENRDD is rarely considered in the differential diagnosis in the absence of lymph node involvement. Lesions of ENRDD resemble many other histiocytic and histiocyte-rich lesions of the head and neck. This makes the diagnosis of ENRDD challenging with the potential for under diagnosis or misdiagnosis and delay in treatment.

Fine-needle aspiration specimens of 3 cases of intra-abdominal Rosai-Dorfman disease with comprehensive review of the literature

INTRODUCTION

Rosai-Dorfman disease (RDD) is a rare usually self-limited non-Langerhans cell histiocytosis of unknown etiology. Nodal and extranodal RDD appear to represent distinct conditions with different molecular alterations and prognosis. They also pose different diagnostic challenges on biopsies and fine-needle aspiration (FNA) cytology. The aim of this study was to report on 3 cases of intra-abdominal RDD and perform an extensive review of the literature on FNA findings of RDD.

MATERIALS AND METHODS

We reviewed FNA specimens from cases diagnosed histologically or cytologically as RDD during the past 10 years. We searched the PubMed and Google Scholar databases for cases of RDD sampled by FNA.

RESULTS

We identified 3 cases of intra-abdominal RDD, involving the kidney, periportal lymph node, and pancreas. FNA of the latter was hypocellular with fibrosis and was nondiagnostic. FNA of the first 2 yielded hypercellular smears that were diagnosed as RDD due to the identification of emperipolesis occurring in large uni- or binucleated histiocytes with large nuclei, fine chromatin, and prominent nucleoli in smears and cell-block sections. Immunohistochemistry showed positive staining for S100 and CD68 and negative staining for CD1a. The large histiocytes with emperipolesis were more difficult to identify histologically and their demonstration required immunohistochemical stains.

CONCLUSION

Our experience and an extensive review of the literature suggest that extranodal RDD can be diagnosed on FNA, and that the recognition of histiocytes with emperipolesis may be less challenging cytologically than histologically. The fibrosis frequently seen in extranodal RDD may lead to nondiagnostic aspirates, however.

Systemic Histiocytosis (Langerhans Cell Histiocytosis, Erdheim-Chester Disease, Destombes-Rosai-Dorfman Disease): from Oncogenic Mutations to Inflammatory Disorders

PURPOSE OF REVIEW

Provide an overview of recent progress in decoding the pathogenesis and treatment of systemic histiocytoses.

RECENT FINDINGS

Advances in molecular techniques over the last few years, enabling the identification of several MAPK mutations in lesion histiocytes, have revolutionized our understanding of histiocytosis that led to a revised classification and new treatments. Since the 2010 discovery of the BRAF^V600E mutation in 57% of Langerhans cell histiocytosis (LCH) lesions, several other kinase mutations have been found, mostly in the MAPK pathway, and also in other key signaling pathways, in LCH, Erdheim-Chester Disease (ECD) and, less frequently, Destombes-Rosai-Dorfman disease (RDD). Those revolutionary breakthroughs enhanced our understanding of the pathogenesis of histiocytosis and led to trials with targeted therapies that demonstrated notable efficacy.

Thyroid Rosai-Dorfman disease with infiltration of IgG4-bearing plasma cells associated with multiple small pulmonary cysts

Background

Rosai-Dorfman disease (RDD) is a rare histiocytosis which involves principally lymph nodes. Thyroid involvement in RDD is a very rare situation, and lung involvement is even rarer.

Case presentation

We report the case of a 46-year-old woman presenting a painless mass in the right side of the neck and subacute dyspnoea. Computerised tomography (CT) scans of the neck and thorax showed a large thyroid mass causing tracheal stenosis and multiple cystic lesions in both lungs. Subtotal thyroidectomy with a tracheal segment resection and histological analysis confirmed the diagnosis of nodal and extranodal (thyroid, tracheal and probably lung) Rosai-Dorfman disease (RDD) with the presence of increased numbers of IgG4-bearing plasma cells. Clinical, functional and radiological follow up 4 years after surgery without medical treatment did not show any disease progression.

Conclusions

This case report indicates a benign course of nodal RDD with thyroid and tracheal infiltration following surgical resection, association of typical histological signs of RDD (emperipolesis) with IgG4-related disease features, and that lung cysts might be a manifestation of RDD.

IgG4-related disease: what a hematologist needs to know

IgG4-related disease is a fibro-inflammatory condition that can affect nearly any organ system. Common presentations include major salivary and lacrimal gland enlargement, orbital disease, autoimmune pancreatitis, retroperitoneal fibrosis and tubulointerstitial nephritis. This review focuses on the hematologic manifestations of IgG4-related disease, including lymphadenopathy, eosinophilia, and polyclonal hypergammaglobulinemia. The disease can easily be missed by unsuspecting hematologists, as patients may present with clinical problems that mimic disorders such as multicentric Castleman disease, lymphoma, plasma cell neoplasms and hypereosinophilic syndromes. When IgG4-related disease is suspected, serum protein electrophoresis and IgG subclasses are helpful as initial tests but a firm histological diagnosis is essential both to confirm the diagnosis and to rule out mimickers. The central histopathological features are a dense, polyclonal, lymphoplasmacytic infiltrate enriched with IgG4-positive plasma cells (with an IgG4/IgG ratio >40%), storiform fibrosis, and obliterative phlebitis. Importantly for hematologists, the latter two features are seen in all tissues except bone marrow and lymph nodes, making these two sites suboptimal for histological confirmation. Many patients follow an indolent course and respond well to treatment, but a significant proportion may have highly morbid or fatal complications such as periaortitis, severe retroperitoneal fibrosis or pachymeningitis. Corticosteroids are effective but cause new or worsening diabetes in about 40% of patients. Initial response rates to rituximab are high but durable remissions are rare. More intensive lymphoma chemotherapy regimens may be required in rare cases of severe, refractory disease, and targeted therapy against plasmablasts, IgE and other disease biomarkers warrant further exploration.

Consensus recommendations for the diagnosis and clinical management of Rosai-Dorfman-Destombes disease

Rosai-Dorfman-Destombes disease (RDD) is a rare non-Langerhans cell histiocytosis characterized by accumulation of activated histiocytes within affected tissues. RDD, which now belongs to the R group of the 2016 revised histiocytosis classification, is a widely heterogeneous entity with a range of clinical phenotypes occurring in isolation or in association with autoimmune or malignant diseases. Recent studies have found NRAS, KRAS, MAP2K1, and ARAF mutations in lesional tissues, raising the possibility of a clonal origin in some forms of RDD. More than 1000 reports have been published in the English literature; however, there is a lack of consensus regarding approach for the clinical management of RDD. Although in most cases RDD can be observed or treated with local therapies, some patients with refractory or multifocal disease experience morbidity and mortality. Here we provide the first consensus multidisciplinary recommendations for the diagnosis and management of RDD. These recommendations were discussed at the 32nd Histiocyte Society Meeting by an international group of academic clinicians and pathologists with expertise in RDD. We include guidelines for clinical, laboratory, pathologic, and radiographic evaluation of patients with RDD together with treatment recommendations based on clinical experience and review of the literature.

IgG4-related disease: review of the histopathologic features, differential diagnosis, and therapeutic approach

Immunoglobulin G4-related disease (IgG4-RD) is an uncommon disorder that demonstrates characteristic clinicopathologic features including sclerosing lesions with storiform fibrosis, increased IgG4+ plasma cells with an increased IgG4+/IgG+ plasma cell ratio, obliterative phlebitis, and often an increased serum IgG4 level. This review summarizes the characteristic histopathologic and clinical features of IgG4-RD with detailed discussion of the histopathologic characteristics of the most commonly involved anatomic sites. We also present recent advances in our understanding of the pathophysiologic mechanisms of IgG4-RD and discuss updates on the treatment, prognosis, and outcomes of this rare disease, including discussion of the possible association between IgG4-RD and malignancy.

Generalized erythematous and scaly plaques and papules: a rare case of Rosai-Dorfman disease accompanied by multiple myeloma

A 75-year-old male presented with generalized erythematous, scaly plaques and painless lymphadenopathy. Rosai-Dorfman disease was suspected based on clinical manifestations and confirmed by histopathologic and immune reactivity studies performed on the biopsy obtained from the left supraclavicular lymph node. The patient was also diagnosed with multiple myeloma according to urine electrophoresis, serum light chain assay, and bone marrow biopsy, which were initially performed for evaluation of anemia. This report highlights the dermatological manifestations of Rosai-Dorfman disease with generalized painless lymphadenopathy.

[Rosai-Dorfman disease: Diagnosis and therapeutic challenges]

Rosai-Dorfman disease (RDD) was first described by the French pathologist Paul Destombes in 1965. It frequently affects children or young adults and is characterized by the presence of large histiocytes with emperipolesis. More than 50 years after this first description, the pathogenesis of this rare disease is still poorly understood. The revised classification of histiocytoses published in 2016 identified various forms of RDD, from familial RDD to IgG4-associated RDD. Almost 90% of the patients with RDD have cervical lymph nodes involvement although all the organs may virtually be involved. Outcomes are typically favorable. Treatments may be necessary in case of compression or obstruction, and are not well codified. The main therapeutic strategies rely on surgery, radiotherapy, steroids, immunosuppressive drugs or interferon-alpha and cladribine.