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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 ,, , and 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.

These guidelines for the management of patients up to 18 years with Langerhans cell histiocytosis (LCH) have been set up by a group of experts involved in the Euro Histio Net project who participated in national or international studies and in peer reviewed publications. Existing guidelines were reviewed and changed where new evidence was available in the literature up to 2012. Data and publications have been ranked according to evidence based medicine and when there was a lack of published data, consensus between experts was sought. Guidelines for diagnosis, initial clinical work-up, and treatment and long-term follow-up of LCH patients are presented.

Key Points Reactivations of multisystem Langerhans cell histiocytosis (MS-LCH) are reduced by prolonging initial chemotherapy. The previously high mortality of high-risk (risk-organ–positive) MS-LCH in children has been markedly reduced.

Objective To describe the clinical, laboratory, and histopathologic features, current treatment, and outcome of patients with macrophage activation syndrome (MAS) complicating systemic juvenile idiopathic arthritis (JIA). Methods In this multinational, multicenter study, pediatric rheumatologists and hemato‐oncologists entered patient data collected retrospectively into a web‐based database. Results A total of 362 patients, 22% of whom had MAS at the onset of systemic JIA, were included in the study by 95 investigators from 33 countries. The most frequent clinical manifestations were fever (96%), hepatomegaly (70%), and splenomegaly (58%). Central nervous system dysfunction and hemorrhages were recorded in 35% and 20% of the patients, respectively. Platelet count and liver transaminase, ferritin, lactate dehydrogenase, triglyceride, and d‐dimer levels were the sole laboratory biomarkers showing a percentage change of >50% between the pre‐MAS visit and MAS onset. Evidence of macrophage hemophagocytosis was found in 60% of the patients who underwent bone marrow aspiration. MAS occurred most frequently in the setting of active underlying disease, in the absence of a specific trigger. Nearly all patients were given corticosteroids, and 61% received cyclosporine. Biologic medications and etoposide were given to 15% and 12% of the patients, respectively. Approximately one‐third of the patients required admission to the intensive care unit (ICU), and the mortality rate was 8%. Conclusion This study provides information on the clinical spectrum and current management of systemic JIA–associated MAS through the analysis of a very large patient sample. MAS remains a serious condition, as a sizeable proportion of patients required admission to the ICU or died.

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The non-LCH can be classified as JXG family and non-JXG family and subdivided according to fairly clear-cut clinical criteria. Utilization of this type of approach will allow better categorization, easier review of the literature and more accurate therapy decision-making.

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal hyperinflammatory condition. It may occur as a primary (genetic) condition due to mutations in genes important in the cytolytic secretory pathway that cause perforin and granzymes to induce apoptosis in target cells. Primary HLH is divided into familial HLH (FHLH1-5), in which HLH is the only manifestation of disease, and other genetic causes in which HLH is one of several clinical manifestations. The identical clinical findings may arise secondary to infectious, rheumatologic, malignant, or metabolic conditions. Whether primary or secondary, HLH therapy needs to be instituted promptly to prevent irreversible tissue damage. It is helpful to think of HLH as the severe end of the spectrum of hyperinflammatory disorders when the immune system starts to damage host tissues (immunopathology). Therefore, no single clinical feature alone is diagnostic for HLH, and it is important that the entire clinical presentation be considered in making the diagnosis. This article contains a discussion of the genetic background, clinical presentation, diagnostic dilemmas, and features that are helpful in making the diagnosis of HLH, along with a discussion of common problems in its management.