Multicentric Castleman disease: Where are we now?

Analysis of Clinical Characteristics, Pathological Changes and Changes of Interleukin-6 (IL-6) and C-Reactive Protein (CRP) in Children with Castleman's Disease

Background

The aim of this study was to analyze the pathological changes, clinical characteristics and changes in immunity, interleukin-6 (IL-6) and C-reactive protein (CRP) in children with Castleman’s disease (CD).

Material/Methods

A total of 15 CD child patients were enrolled as observation group, while 20 normal children receiving healthy examination were enrolled as healthy control group. The pathological changes, clinical characteristics and changes in immunity and serum IL-6 and CRP expressions were retrospectively analyzed in observation group.

Results

The clinical manifestation of unicentric CD (UCD) was mainly enlargement of cervical lymph nodes without liver-spleen enlargement and fever, and the major pathological type was the hyaline-vascular type. Multicentric CD (MCD) child patients all had anemia, fever and other systemic symptoms, and the major pathological type was the plasma-cell type. There were expressions of the immune indexes, including cluster of differentiation 3 (CD3), CD4, CD8, CD20, and CD79, in a certain degree, while CD138 and VS38C expressions displayed the polyclonal proliferation of plasma cells, rather than neoplastic proliferation. The Epstein-Barr virus and human herpes virus-8 detection results were negative, and CD21 in follicular dendritic cells in abnormal germinal center was positive. The expression levels of serum IL-6 and CRP in observation group were higher than those in control group (P<0.05).

Conclusions

There are immune dysfunction and increased expressions of serum IL-6 and CRP in child patients with CD, so it can be speculated that the immune abnormality and overexpression of serum inflammatory factors may be associated with the occurrence of CD.

A lymphoproliferative pericardial mass

Castleman disease (CD) is a rare lymphoproliferative disorder with variable presentation and prognosis. Most CD cases are unicentric and correspond to the hyaline-vascular variant, a histopathological classification associated with better outcomes, which commonly presents as an enhancing hypervascular mediastinal mass. CD is often asymptomatic and surgically resectable. Nonetheless, surgical resection can be difficult when the lymphoid mass is causing compression of vital structures. We discuss a rare case of hyaline-vascular unicentric CD presenting as an incidental pericardial mass.

[Idiopathic multicentric Castleman's disease]

Idiopathic multicentric Castlemans disease is a rare lymphoproliferative disorder that has many similar laboratory, radiological, clinical and pathological manifestations with various conditions, including IgG4-related disease. Increased activity of cytokines, especially interleukin-6, leads to systemic inflammatory symptoms with the development of lymphadenopathy and rarely extranodal lesions. Histological changes in the lymph nodesin hyaline vascular and plasma cell variants of Castlemans disease are hardly distinguishable from the pattern of reactive, tumor and IgG4-related lymphadenopathy. Idiopathic multicentric Castlemans disease can be diagnosed only when infection with human herpesvirus-8 type and human immunodeficiency virus is excluded. In the article, the authors describe two cases of idiopathic multicentric Castlemans disease, including the first world literature description of extranodal damage of the hip muscle in this disorder. In addition, the authors gave a review of the literature on the main clinical, laboratory and morphological manifestations, which allow confirming the diagnosis of Castlemans disease.

Histologic and Laboratory Characteristics of Symptomatic and Asymptomatic Castleman Disease in the Pediatric Population

OBJECTIVES

Compare the morphologic, laboratory, and clinical features of asymptomatic and symptomatic Castleman disease in the pediatric population.

METHODS

We reviewed clinical records and histopathology of patients with Castleman disease from 2 pediatric institutions.

RESULTS

Of 39 patients with pediatric Castleman disease, 37 had unicentric disease, all classified with the hyaline vascular variant of Castleman disease, 8 of which were clinically symptomatic. These 8 patients demonstrated abnormal laboratory findings, including microcytic anemia, elevated erythrocyte sedimentation rate and C-reactive protein, and hypoalbuminemia. In addition, histopathologic evaluation showed that the 8 symptomatic cases had more hyperplastic germinal centers, fewer atrophic or regressed germinal centers, fewer mantle zones containing multiple germinal centers, reduced "onion skinning" of mantle zones, and fewer "lollipop" formations compared with the asymptomatic cases.

CONCLUSIONS

This series of pediatric Castleman disease showed that lymph nodes from asymptomatic patients generally demonstrated the more classic hyaline vascular histology, whereas those with symptoms could lack or have only focal classic findings. As such, reactive lymph nodes with subtle Castleman-like features should prompt clinical correlation to ensure proper diagnosis.

The Potential Clinical Benefit of Tocilizumab Therapy for Patients with HHV-8-infected AIDS-related Multicentric Castleman Disease: A Case Report and Literature Review

Castleman disease (CD), also known as angiofollicular hyperplasia, is a rare disorder characterized by nonmalignant mediastinal lymph node enlargement provoked by excess interleukin-6 (IL-6) secretion. It could be unicentric or multicentric (MCD). Here, we describe a 27-year-old man with a prior history of AIDS, Kaposi sarcoma (KS), and latent syphilis who presented to the ED for persistent fatigue, fever, chills, night sweats, and productive cough. Infectious workup was negative, and the patient continued to have a high fever despite empiric antibiotic therapy. Bone marrow biopsy was performed and was negative for malignancy. The patient eventually underwent a left clavicular lymph node biopsy, which showed a plasma cell variant CD with positive immunostaining for human herpesvirus 8 (HHV-8), and high HHV-8 viral load. We started the patient on rituximab and liposomal doxorubicin, but unfortunately, the patient had a severe anaphylactic reaction to the rituximab, so we could not proceed with this treatment. We, therefore, started tocilizumab treatment, which improved the patient's general condition, and he was eventually discharged from our hospital. Upon follow-up 11-months later, a repeat CT scan of the chest and abdomen showed a near-complete treatment response with decreased lymphadenopathy throughout and hepatosplenomegaly. IL-6 overproduction in patients with CD is linked to the production of inflammatory cytokines and has a role in tumor angiogenesis, which makes it potential for IL-6 targeted therapy. The diagnosis of CD, especially MCD, requires a high index of suspicion, and a lymph node biopsy is essential in the diagnosis. Tocilizumab, an IL-6 receptor antibody, could potentially be considered as a practical therapeutic approach in managing HHV-8 positive MCD patients who do not tolerate or respond to initial rituximab therapy.

Thrombocytopenia, Anasarca, Fever, Reticulin Fibrosis/Renal Failure, and Organomegaly (TAFRO) Syndrome with Bilateral Adrenal Hemorrhage in Two Caucasian Patients

Case series

Patients: Male, 19-year-old • Female, 31-year-old

Final Diagnosis: TAFRO syndrome

Symptoms: Fever • splenomegaly • lymphadenopathies

Medication: —

Clinical Procedure: —

Specialty: Hematology

HIV-associated multicentric Castleman disease: a report of 19 cases at an oncology institution

The aim of this study is to describe the clinical characteristics and outcome of multicentric Castleman disease (MCD) in HIV-infected patients at an oncological referral center in Mexico. Clinical records at the HIV-AIDS clinic of all patients diagnosed with MCD from 1994 to 2018 were reviewed. There were 19 patients, mean age was 31.3 ± 8.4 years, and 17 (89.5%) were males. Fifteen patients (79%) had also Kaposi sarcoma (KS). Main clinical characteristics were multiple lymphadenopathy (95%), systemic symptoms (63%), and hepatosplenomegaly (50%). Computed tomography scan and 2-[18F]-fluoro-2-deoxy-d-glucose positron emission tomography showed multiple lymphadenopathy, inversion of the liver:spleen uptake ratio, with an increase in SUVmax (5.7). The histopathology report described plasma cells in 58%, mixed type in 26%, and hyaline vascular in 16%. Eleven patients (57.9%) received different chemotherapy regimens. Seven patients died (36.8%): four related to MCD progression or chemotherapy complications, median survival was eight months. For those patients who survived, median, follow-up was 28 months (p < 0.001). The incidence of MCD in people living with HIV is probably underestimated. In patients with lymphadenopathy, B symptoms, deranged inflammatory markers, and/or disseminated KS, a biopsy of an enlarged lymph node is warranted, and the histology should be reviewed by an experienced pathologist.

51-year old man with tingling, burning and progressive limb weakness

Peripheral neuropathy is a common reason for referral to neurology. Chronic acquired demyelinating neuropathies are an important and varied group with overlapping presentations, and may have an immune-mediated cause. Their correct diagnosis is important as they respond to different treatments; timely intervention can prevent irreversible axonal degeneration. We present a case that highlights the approach to an adult presenting with a chronic demyelinating neuropathy.

[Indolent T-lymphoblastic proliferation in association with localized Castleman disease: A case report]

Herein we report the case of a 41-year-old woman who presented with pelvic pain. Magnetic Resonance Imaging exhibited a single pelvic mass, measuring 50mm long axis, alongside the right iliac vessels. Histological examination of the excision specimen showed a lymphoid tumor with features of localized Castleman disease, hyaline vascular type. Moreover we identified multiple interfollicular dark clusters, composed of cells morphologically resembling cortical thymocytes. Their immunophenotype was consistent with an intermediate stage of T-cell differentiation, with the expression of CD3, CD4, CD8, TdT, CD1a, CD99, CD2, CD5, CD7 and CD10, with 40% Ki67. After integration of clinical and molecular data, the retained diagnosis was an indolent T-cell lymphoblastic proliferation associated with hyaline vascular localized Castleman disease. The clinical course confirmed the indolent nature of the proliferation, despite a late local recurrence at 7 years of the initial diagnosis, without histological modification, due to an incomplete initial resection surgery.

Unicentric Castleman disease presenting as a retroperitoneal peripancreatic mass: A report of two cases and review of literature

Castleman disease (CD) is a rare disorder of lymph nodes and related tissues. CD generally occurs in the mediastinum, as well as in cervical, retroperitoneal and axillary regions. The disease is classified into two major types: unicentric CD (UCD) and multicentric CD. The occurrence of UCD in the retroperitoneal peripancreatic region is quite rare. We encountered two cases of retroperitoneal peripancreatic UCD in our hospital during the past three years. Following a series of medical examinations, including magnetic resonance imaging, computed tomography, ultrasonography and postoperative histopathological examination, these two patients were diagnosed with UCD, which presented as a retroperitoneal peripancreatic mass. The mass in each patient was completely excised, and no postoperative radiochemotherapy was administered. Both patients recovered well without recurrence during a follow-up period of 30 mo and 8 mo.

Renal failure in pediatric Castleman disease: Four French cases with thrombotic microangiopathy

Pediatric Castleman disease (CD) is an uncommon and poorly understood disorder of the lymph nodes. Renal failure has not been described in pediatric multicentric CD (MCD). We report four cases, who presented with polyadenopathy, organomegaly, edema and fluid accumulations, high blood pressure, and acute renal failure. In all cases, renal biopsy confirmed diffuse thrombotic microangiopathy. Definitive diagnosis of MCD was made by a biopsy of an affected lymph node located by computer tomography before initiation of corticosteroid therapy. Treatment of CD with corticosteroid therapy and rituximab was rapidly effective without relapse to date.

Epstein-Barr Virus-Induced Metabolic Rearrangements in Human B-Cell Lymphomas

Tumor metabolism has been the object of several studies in the past, leading to the pivotal observation of a consistent shift toward aerobic glycolysis (so-called Warburg effect). More recently, several additional investigations proved that tumor metabolism is profoundly affected during tumorigenesis, including glucose, lipid and amino-acid metabolism. It is noticeable that metabolic reprogramming can represent a suitable therapeutic target in many cancer types. Epstein–Barr virus (EBV) was the first virus linked with cancer in humans when Burkitt lymphoma (BL) was described. Besides other well-known effects, it was recently demonstrated that EBV can induce significant modification in cell metabolism, which may lead or contribute to neoplastic transformation of human cells. Similarly, virus-induced tumorigenesis is characterized by relevant metabolic abnormalities directly induced by the oncoviruses. In this article, the authors critically review the most recent literature concerning EBV-induced metabolism alterations in lymphomas.

Ancient cancers and infection-induced oncogenesis

Cancers have been reported in bone and soft tissue of ancient agricultural populations. Fossilized bones from prehistoric periods provide evidence of tumors but only one example of cancer. Difficulties in diagnosing the causes of lesions in mummified tissue and fossilized bone, and in interpreting the prevalence of cancers from remains, draw attention to the need for complementary approaches to assess the occurrence of cancer in ancient populations. This paper integrates current knowledge about pathogen induction of cancer with phylogenetic analyses of oncogenic pathogens, and concludes that pathogen-induced cancers were probably generally present in ancient historic and prehistoric human populations. Consideration of cancers in extant human populations and wildlife lends credence to this conclusion, with the caveat that the presence of cancers may depend on population-specific exposures to oncogenic parasites and carcinogens.

Multicentric Castleman's disease in human immunodeficiency virus infection: two case reports

Background

Castleman’s Disease is a rare B-cell lymphoproliferative disease. It is mostly benign and is characterized by non-neoplastic lymph node hypertrophy, associated with infection by human herpesvirus-8 in people with the human immunodeficiency virus/acquired immunodeficiency syndrome. Although the unicentric or localized form presents as benign, the multifocal form can manifest severe systemic symptoms. We report two unusual cases of men presenting cervical enlarged lymph nodes that were believed to be infectious.

Case presentation

The first case is a 41-year-old feoderm man who presented to the Department of Infectious Diseases of the Hospital das Clínicas in May 2015, with irregular fever history (38–39 °C), dyspnea, weight loss (8 kg/1 year), and asthenia with increased cervical lymph nodes of 1-year duration. His immunohistochemical diagnosis presented Castleman’s disease in plasmacytic/diffuse form. In the second case, a 35-year-old feoderm man presented at the same hospital with multiple cervical enlarged lymph nodes and histopathological evidence of Castleman’s disease associated with human herpesvirus-8.

Conclusion

Considering the importance of differential diagnosis of lymphoid disorders, Castleman’s disease is a challenging diagnosis in people living with human immunodeficiency virus/acquired immunodeficiency syndrome and can be easily misdiagnosed when lymphoid disorders are present in the human immunodeficiency virus/acquired immunodeficiency syndrome population due to nonspecific symptoms and signs.

A rare case of multicentric castleman's disease transforms into multiple myeloma and its successful treatment

Multicentric Castleman's disease (MCD) is a rare kind of lymphoproliferative disorder characterized by systemic problems such as frequent fever, fatigue and weight loss with angiofollicular lymph node hyperplasia. However, unlike unicentric Castleman's disease (UCD) with long-time survival by surgery and local radiotherapy, MCD remains poor prognosis due to no well-defined optimal treatment strategies and high risk of developing malignances especially lymphoma. We reported a case of MCD who received chemotherapy by ECHOP with unsatisfactory outcome and then oral administration with thalidomide combined with prednisone without disease progression after therapy. After 3 y, his MCD turned into multiple myeloma (MM) and accompanied by obvious response to combination of thalidomide with prednisone. Nowadays, there is no standard of therapy yet established for MCD. We successfully treated one such patient and found thalidomide based therapy may have a significant effect on MCD. We also proposed further researches with therapeutic potential about thalidomide for MCD.

Idiopathic multicentric Castleman's disease: a clinicopathologic study in comparison with IgG4-related disease

The present study aimed to compare clinicopathologic features between idiopathic multicentric Castleman's disease (n=22) and IgG4-related disease (n=26). Histology was analyzed using lymph node and lung biopsies. The expression of IL-6 mRNA in tissue was also examined by in situ hybridization and real-time PCR. Patients with idiopathic multicentric Castleman's disease were significantly younger than those with IgG4-related disease (p<0.001). Splenomegaly was observed in only idiopathic multicentric Castleman's disease (p=0.002), while pancreatitis and sialo-dacryoadenitis were restricted to IgG4-related disease (both p<0.001). Serum IgG4 concentrations were commonly elevated at >135 mg/dL in both groups (p=0.270). However, the IgG4/IgG ratio in IgG4-related disease was significantly higher than that in Castleman's disease (p<0.001). Histologically, sheet-like plasmacytosis was highly characteristic of idiopathic multicentric Castleman's disease (p<0.001), while plasmacytic infiltration in IgG4-related disease was always associated with intervening lymphocytes. Similar to laboratory findings, the IgG4/IgG-positive plasma cell ratio, but not the IgG4-positive cell count, was significantly higher in IgG4-related disease (p=0.002). Amyloid-like hyalinized fibrosis was found in 6/8 lung biopsies (75%) of Castleman's disease. The over-expression of IL-6 mRNA was not confirmed in tissue samples of Castleman's disease by either in situ hybridization or quantitative real-time PCR. In conclusion, useful data for a differential diagnosis appear to be age, affected organs, the serum IgG4/IgG ratio, sheet-like plasmacytosis in biopsies, and the IgG4/IgG-positive cell ratio on immunostaining. Since IL-6 was not over-expressed in tissue of idiopathic multicentric Castleman's disease, IL-6 may be produced outside the affected organs, and circulating IL-6 may lead to lymphoplasmacytosis at nodal and extranodal sites.

Treatment of Kaposi Sarcoma Herpesvirus-Associated Multicentric Castleman Disease

Kaposi sarcoma herpesvirus (KSHV)-associated multicentric Castleman disease (MCD) is a rare, polyclonal lymphoproliferative disorder characterized by flares of inflammatory symptoms, edema, cytopenias, lymphadenopathy, and splenomegaly. Diagnosis requires a lymph node biopsy. Pathogenesis is related to dysregulated inflammatory cytokines, including human and viral interleukin-6. Rituximab alone or in combination with chemotherapy, such as liposomal doxorubicin, has led to an overall survival of over 90% at 5 years. Experimental approaches to treatment include virus activated cytotoxic therapy with high-dose zidovudine and valganciclovir and targeting human interleukin-6 activity. Despite successful treatment of KSHV-MCD, patients remain at high risk for developing non-Hodgkin lymphomas.

Pathology of Castleman Disease

The term Castleman disease encompasses several distinct lymphoproliferative disorders with different underlying disease pathogenesis, and clinical outcomes. It includes unicentric and multicentric diseases with limited versus significant systemic symptoms, respectively. Importantly, the histopathologic features encountered in the various forms of Castleman disease are diverse, and for the most part, lack specificity, because they are seen to varying degrees in different clinical variants of Castleman disease, and in reactive (autoimmune/infectious) and malignant (lymphoma) contexts. Accordingly, accurate clinical diagnosis of Castleman disease requires careful and thorough clinicopathologic correlation. An overview of the key histopathologic features of Castleman disease is presented.

The full spectrum of Castleman disease: 273 patients studied over 20 years

The spectrum of Castleman disease (CD) has considerably extended since its first description in 1956. Recently, an international collaborative working group has reached consensus on the diagnostic criteria and classification of CD. We herein report 273 patients with lymph node histopathology consistent with CD and investigate the newly established diagnostic criteria. Twenty of these patients with Castleman-like histopathology were removed from analyses, because they were diagnosed with an exclusionary disorder (18 with haematological malignancy). Among the 253 remaining patients, 57 were considered unicentric CD (UCD), 169 were multicentric CD associated with Human Herpesvirus 8 (HHV-8+MCD), including 140 patients with human immunodeficiency virus (HIV) infection and 29 patients without HIV infection, and 27 were HHV-8 negative/idiopathic multicentric CD (iMCD). 2-(¹⁸ F)fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography was useful in 62 patients for staging/classification of the disease and for excluding associated lymphoma. UCD was mainly associated with hyaline-vascular histopathological features, and most patients were asymptomatic. Of the 27 patients that we had originally diagnosed with iMCD, 26 met the newly established diagnostic criteria. Patients with iMCD and HHV-8+ MCD demonstrated similar characteristics, including fever, splenomegaly, cytopenia and inflammatory symptoms. However, the disease was more aggressive in HHV-8+ MCD, particularly in HIV-infected patients.

TAFRO syndrome: A case report and review of the literature

TAFRO syndrome is a rare clinicopathologic variant of idiopathic multicentric Castleman disease characterized by Thrombocytopenia, Ascites (anasarca), myeloFibrosis, Renal dysfunction, and Organomegaly. Here, we report a case of TAFRO syndrome in an HIV-negative young Caucasian male who presented with fever, normocytic anemia, thrombocytopenia, and acute renal insufficiency. The serum interleukin-6 (IL-6) level was elevated. Chest and abdominal CT revealed bilateral pleural effusion, ascites, splenomegaly, and multiple mildly enlarged lymph nodes. An excisional biopsy of inguinal lymph node showed a few atrophic follicles and expansion of interfollicular areas by marked vascular proliferation and polytypic plasmacytosis. HHV-8 was negative. Subsequent bone marrow biopsy was normocellular with moderately increased megakaryocytes and occasional megakaryocytic emperipolesis. His signs and symptoms improved after treatment with methylprednisolone and tocilizumab (anti-IL-6 receptor antibody). Our study confirms the distinctive nature of this syndrome, which should allow for better recognition and appropriate therapy.

Lipids, lipid metabolism and Kaposi's sarcoma-associated herpesvirus pathogenesis

Lipids are essential for mammalian cells to maintain many physiological functions. Emerging evidence has shown that cancer cells can develop specific alterations in lipid biosynthesis and metabolism to facilitate their survival and various malignant behaviors. To date, the precise role of cellular lipids and lipid metabolism in viral oncogenesis is still largely unclear with only a handful of literature covering this topic to implicate lipid metabolism in oncogenic virus associated pathogenesis. In this review, we focus on the role of lipid biosynthesis and metabolism in the pathogenesis of the Kaposi's sarcoma-associated herpesvirus, a common causative factor for cancers arising in the immunocompromised settings.

Fever and generalised lymphadenopathy in an HIV-positive patient: a diagnostic challenge

Fever and generalised lymphadenopathy is a common presentation of a variety of diseases and a thorough investigation is often necessary for appropriate diagnosis.We present a 53-year-old male patient admitted with fever, weight loss of 15 kg in 3 months and abdominal discomfort. Examination was only remarkable for axillary and inguinal lymphadenopathy. Blood tests showed normocytic normochromic anaemia, cholestasis and a previously unknown HIV-1 infection with lymphocyte CD4 +count of 239 cells/mm³ and viral load 3.172.370 copies/mL. A body CT scan showed multiple axillary, mediastinal, lumbar, aortic, iliac and pelvic lymphadenopathy as well as hepatosplenomegaly. An excisional biopsy of the left axillary lymphadenopathy was performed and histology ultimately revealed multicentric Castleman's disease associated with Human Herpes Virus-8. After initiation of antiretroviral therapy, rituximab was given and progressive clinical improvement occurred.

Extrafollicular activities: perspectives on HIV infection, germinal center-independent maturation pathways, and KSHV-mediated lymphoproliferation

Early events in the pathogenesis of KSHV-associated lymphoproliferations in the context of HIV disease remain poorly understood. Recent research indicates that latent HIV infection causes persistent immune dysfunction in B cell follicles. Simultaneously, lack of T cell immune surveillance in the lymph nodes dysregulates the biology of EBV. In sum, these defects bias B lymphocyte maturation away from traditional T cell-dependent germinal center-mediated pathways and towards extrafollicular pathways. Recent advances in B lymphocyte immunology suggest that extrafollicular maturation pathways for antibody secreting cells are more flexible and robust than previously believed. These responses are now understood to be both durable and antigen-specific, and even canonically germinal center-restricted events such as class switch recombination and somatic hypermutation have now been demonstrated in an extrafollicular context. As a lymphotrophic pathogen which causes disease primarily in the context of HIV and EBV co-infection, future studies examining the interactions of KSHV biology with extrafollicular B cell maturation pathways will be critical to uncovering key aspects of KSHV-mediated immune pathology.

Human herpesvirus 8-related diseases: Histopathologic diagnosis and disease mechanisms

The emergence of HIV/AIDS more than three decades ago led to an increased incidence of diseases caused by HHV8 co-infection, particularly Kaposi sarcoma, primary effusion lymphoma, and multicentric Castleman disease. Over time, the development of highly effective AIDS therapies has resulted in a decreased incidence of HHV8-associated entities, which are now more commonly found in patients with undiagnosed and/or untreated AIDS. Due to their rarity, some of these diseases may be difficult to recognize without appropriate clinical information. This article provides an overview of HHV8-related disorders, with a focus on their morphologic and phenotypic features, and includes a brief overview of laboratory methods used to detect HHV8. Disease mechanisms by which the HHV8 virion promotes tumorigenesis are also reviewed.

International, evidence-based consensus diagnostic criteria for HHV-8-negative/idiopathic multicentric Castleman disease

Human herpesvirus-8 (HHV-8)-negative, idiopathic multicentric Castleman disease (iMCD) is a rare and life-threatening disorder involving systemic inflammatory symptoms, polyclonal lymphoproliferation, cytopenias, and multiple organ system dysfunction caused by a cytokine storm often including interleukin-6. iMCD accounts for one third to one half of all cases of MCD and can occur in individuals of any age. Accurate diagnosis is challenging, because no standard diagnostic criteria or diagnostic biomarkers currently exist, and there is significant overlap with malignant, autoimmune, and infectious disorders. An international working group comprising 34 pediatric and adult pathology and clinical experts in iMCD and related disorders from 8 countries, including 2 physicians that are also iMCD patients, was convened to establish iMCD diagnostic criteria. The working group reviewed data from 244 cases, met twice, and refined criteria over 15 months (June 2015 to September 2016). The proposed consensus criteria require both Major Criteria (characteristic lymph node histopathology and multicentric lymphadenopathy), at least 2 of 11 Minor Criteria with at least 1 laboratory abnormality, and exclusion of infectious, malignant, and autoimmune disorders that can mimic iMCD. Characteristic histopathologic features may include a constellation of regressed or hyperplastic germinal centers, follicular dendritic cell prominence, hypervascularization, and polytypic plasmacytosis. Laboratory and clinical Minor Criteria include elevated C-reactive protein or erythrocyte sedimentation rate, anemia, thrombocytopenia or thrombocytosis, hypoalbuminemia, renal dysfunction or proteinuria, polyclonal hypergammaglobulinemia, constitutional symptoms, hepatosplenomegaly, effusions or edema, eruptive cherry hemangiomatosis or violaceous papules, and lymphocytic interstitial pneumonitis. iMCD consensus diagnostic criteria will facilitate consistent diagnosis, appropriate treatment, and collaborative research.