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A vast body of evidence provides support to a central role of exaggerated production of interferon-γ (IFN-γ) in causing hypercytokinemia and signs and symptoms of hemophagocytic lymphohistiocytosis (HLH). In this chapter, we will describe briefly the roles of IFN-γ in innate and adaptive immunity and in host defense, summarize results from animal models of primary HLH and secondary HLH with particular emphasis on targeted therapeutic approaches, review data on biomarkers associated with activation of the IFN-γ pathway, and discuss initial efficacy and safety results of IFN-γ neutralization in humans.

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Hemophagocytic lymphohistiocytosis (HLH) is a severe life-threatening hematological disorder characterized by the dysregulation of the immune system and a hyperinflammatory response. Prompt treatment is crucial to prevent fatality. Although primarily affecting infants, HLH can also occur in children and adults. It is classified as primary and secondary, with primary HLH being genetic and predominantly affecting children. Secondary HLH is triggered by infections, malignancy, metabolic disorders, and rheumatological conditions. Diagnosis is based on the HLH-2004 criteria, considering clinical and laboratory parameters. Early diagnosis and treatment improve prognosis. Treatment follows the HLH-94 and HLH-2004 protocol and consists of eight weeks of induction therapy with cyclosporine, corticosteroids, and etoposide. This case describes a 26-year-old female diagnosed with HLH and successfully treated according to the protocol. The patient exhibited improvement and was discharged, demonstrating the importance of early diagnosis and appropriate management in adult HLH cases.

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Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening hyperinflammatory syndrome characterized by profound immune system activation. In adults, most cases of HLH are due to an underlying pathology- such as infection, malignancy, or autoimmune disease. It is a disease that can progress to rapid clinical deterioration and be difficult to diagnose. Nevertheless, regardless of etiology, most patients with HLH benefit from treatment. This paper highlights the challenges involved in diagnosing and managing this condition in practice, with an emphasis on how young, previously healthy young adults can present in a critically ill state.

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BACKGROUND: The contribution of genetic factors to the severity of adult hemophagocytic lymphohistiocytosis (HLHa) remains unclear. OBJECTIVE: We sought to assess a potential link between HLHa outcomes and HLH-related gene variants. METHODS: Clinical characteristics of 130 HLHa patients (age ≥ 18 years and HScore ≥ 169) and genotype of 8 HLH-related genes (LYST, PRF1, UNC13-D, STX11, STXBP2, RAB27A, XIAP, and SAP) were collected. A total of 34 variants found in only 6 genes were selected on the basis of their frequency and criteria predicted to impair protein function. Severity was defined by refractory disease to HLH treatment, death, or transfer to an intensive care unit. RESULTS: HLHa-associated diseases (ADs) were neoplasia (n = 49 [37.7%]), autoimmune/inflammatory disease (n = 33 [25.4%]), or idiopathic when no AD was identified (n = 48 [36.9%]). Infectious events occurred in 76 (58.5%) patients and were equally distributed in all ADs. Severe and refractory HLHa were observed in 80 (61.5%) and 64 (49.2%) patients, respectively. HScore, age, sex ratio, AD, and infectious events showed no significant association with HLHa severity. Variants were identified in 71 alleles and were present in 56 (43.1%) patients. They were distributed as follows: 44 (34.4%), 9 (6.9%), and 3 (2.3%) patients carrying 1, 2, and 3 variant alleles, respectively. In a logistic regression model, only the number of variants was significantly associated with HLHa severity (1 vs 0: 3.86 [1.73-9.14], P = .0008; 2-3 vs 0: 29.4 [3.62-3810], P = .0002) and refractoriness (1 vs 0: 2.47 [1.17-5.34], P = .018; 2-3 vs 0: 13.2 [2.91-126.8], P = .0003). CONCLUSIONS: HLH-related gene variants may be key components to the severity and refractoriness of HLHa.

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Hemophagocytic lymphohistiocytosis (HLH) is an uncommon condition that can be fatal due to overwhelming macrophage activation and cytokine production. It can be primary (familial/genetic) or secondary. It is associated with infections, malignancies, and rheumatologic and immunodeficiency disorders. We report a middle-aged female patient with sickle cell anemia who presented with COVID-19 infection that triggered a vaso-occlusive crisis and resulted in HLH. She had preexisting high ferritin levels and cytopenias, making the diagnosis more challenging. A high index of suspicion and timely treatment is essential to prevent adverse outcomes.

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Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory syndrome characterized by cytokine storms leading to multi-organ dysfunction and is a highly fatal disease. Infectious diseases are the most common cause of secondary HLH. A wide variety of infections can lead to secondary HLH.  In this case series, we report five cases of HLH which had different therapeutic approaches and varied clinical courses, with one of them diagnosed as a rare entity of coronavirus disease 2019 (COVID-19)-associated HLH of multisystem inflammatory syndrome in children (MISC) spectrum, one case each of idiopathic HLH, staphylococcal infection-associated secondary HLH, leptospirosis with secondary HLH and dengue-associated HLH. The case of idiopathic HLH required initiation of immunosuppressive therapy but had a fatal outcome while others were treated successfully with antibiotics, steroids, intravenous immunoglobulin and supportive therapy. Our case series highlights the importance of evaluating for all possible infective causes thoroughly in HLH. Most patients can be managed without chemotherapy by treating the secondary causes of HLH, including common tropical infections and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

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Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal hyper-inflammatory state that is caused by a highly activated but ineffective immune system. It can be primary or secondary to triggers like infections, malignancies, and autoimmune conditions. The authors present the case of a young male with a fever and abdominal pain due to typhoid. He continued to have a high-spiking fever and developed dyspnea, requiring oxygen therapy despite being treated with appropriate antibiotics. Laboratory evaluation revealed cytopenias and deranged liver function tests, and abdominal imaging revealed hepatosplenomegaly. These clinical and laboratory findings raised suspicion of HLH secondary to typhoid fever. Further investigations were suggestive of hyperferritinemia and hypofibrinogenemia, and bone marrow aspirates showed hemophagocytes. The patient was treated with immunosuppression (dexamethasone) and antibiotics and showed remarkable recovery. Hemophagocytic lymphohistiocytosis should be suspected in patients with tropical infections like enteric fever, tuberculosis, malaria, dengue, etc. that worsen despite appropriate treatment, as late diagnosis is associated with greater mortality.

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Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening condition characterized by hyperinflammation in an uncontrolled and ineffective immune response. Despite great improvement in diagnosis and treatment, it still represents a challenge in clinical management, with poor prognosis in the absence of an aggressive therapeutic approach. The present literature review focuses on secondary HLH at pediatric age, which represents a heterogeneous group in terms of etiology and therapeutic approach. It summarizes the most recent evidence on epidemiology, pathophysiology, diagnosis, treatment and prognosis, and provides a detailed description and comparison of the major subtypes of secondary HLH. Finally, it addresses the open questions with a focus on diagnosis and new treatment insights.

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OBJECTIVE: Hemophagocytic lymphohistiocytosis (HLH) is a rare life-threatening, hyperinflammatory syndrome usually treated with high-dose steroids (HDS), often complemented with adjunct therapies, such as etoposide (HLH-94 protocol). Anakinra has been reported to effectively treat HLH; however, has not been comparatively examined with etoposide-based therapies. We sought to evaluate the effectiveness and durability of these treatment approaches. METHODS: We performed a retrospective analysis of all adult patients diagnosed with secondary HLH between January 2011 and November 2022 who received anakinra and HDS, the HLH-94 protocol, HDS alone, or supportive care. RESULTS: Thirty adult patients with secondary HLH were included. Cumulative incidence (CI) of response at 30 days was 83.3%, 60%, and 36.4% for patients treated with anakinra, the HLH-94 protocol, and HDS alone, respectively. CI of relapse at 1 year was 50%, 33.3%, and 0% with the HLH-94 protocol, HDS, and anakinra and HDS, respectively. Overall survival at 1 year was higher with anakinra and HDS compared to the HLH-94 protocol, yet was not statistically significant (77.8% vs. 33.3%; hazard ratio: 0.29; p = .25). CONCLUSION: Treatment with anakinra and HDS in adults with secondary HLH was associated with higher response rates with longer survival compared with alternative therapies and should be further investigated in this setting.

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Hemophagocytic lymphohistiocytosis (HLH) is a hematological disorder that results from an uncontrolled activation of the immune system, which can then lead to multisystem organ failure. Given the nonspecific nature of this illness, it can go undetected for too long, thereby causing permanent damage to organ systems. In adults, HLH has been associated with a number of infectious etiologies, particularly viral infections. Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to a global pandemic and has been associated with acute respiratory distress syndrome (ARDS). Among its other manifestations, COVID-19 has also been linked to HLH. In this report, we describe a case of a male patient who presented with multisystem organ failure and was found to have HLH. Since no clear etiology for his HLH could be elicited, it was determined to be a result of his recent COVID-19 infection.

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Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening syndrome involving excessive immune activation. It can be primary (familial) or secondary (triggered by infection, malignancy, or rheumatological disease). This is a case of a previously healthy 43-year-old African American woman who presented with fever and confusion. The patient was eventually diagnosed with pulmonary aspergillosis and responded well to antifungal therapy. She met the diagnostic criteria of HLH-2004 trial for hemophagocytic lymphohistiocytosis. She also fulfilled the 2019 classification criteria for systemic lupus erythematosus (SLE) without the classical signs and symptoms of SLE. HLH management includes supportive management, treatment of underlying condition, and immunosuppressive treatment. Etoposide and dexamethasone are commonly used treatments for HLH; however, underlying active infection can limit the treatment options. In our case, the patient was treated with steroids and hydroxychloroquine. Her condition gradually improved and she recovered without complications. Based on our literature review, we encountered six cases of HLH secondary to Aspergillosis with a mean age of approximately 47 years. The diagnosis of HLH is often delayed because of nonspecific presentation. Early identification and treatment are crucial to improve the survival rate.

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Hemophagocytic lymphohistiocytosis (HLH) is a hyperactivation syndrome associated with the overactivation of macrophages, which produce enormous amounts of tumor necrosis factor-alpha and interferon-gamma. HLH often presents with diminished T-cell and natural killer (NK) cell regulation, which can develop due to underlying genetic causes, infections, autoimmune diseases, and/or secondary to malignancies. Here, we describe the case of a 39-year-old man who presented with subjective fevers and fatigue. Further workup revealed hyperferritinemia, hypertriglyceridemia, and absent NK-cell activity, which raised a strong suspicion for HLH. The workup also revealed elevated aminotransferases signaling hepatic involvement that was attributed to HLH. Bone marrow biopsy revealed hypercellularity instead of the hemophagocytosis usually seen in HLH. Flow cytometry revealed acute B-cell lymphocytic leukemia, which was identified as the cause of HLH in our patient. This case highlights the rare presentation of HLH secondary to a B-cell malignancy. It addresses the importance of high clinical suspicion in patients with high fevers despite the use of broad-spectrum antibiotics. There is limited information on the treatment of HLH secondary to malignancies specifically, and further research in this area is needed to increase the survival rate.

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Anti-cytokine therapies have been gaining attention as a means of improving outcomes in adult secondary HLH (asHLH), which currently has poor outcomes when treated with standard etoposide-based therapies. Anakinra is an interleukin-1 antagonist that is increasingly being used in the management of asHLH. Here is described a multi-hospital series of 16 adult patients with secondary HLH treated with anakinra. Provoking factors of secondary HLH included hematologic malignancy (n = 7, 44%), bacterial infection (n = 7, 44%), viral infection (n = 5, 31%), rheumatologic disorder (n = 4, 25%), and unknown (n = 1, 6%). Five patients remained alive at time of last follow-up (OS = 31%). Median OS was 1.7 months from initiation of anakinra (range 0.2-59). OS among patients with rheumatologic causes of secondary HLH was 75%, whereas only 17% of patients with other provoking factors survived (p = 0.0293). Anakinra was well tolerated, with only 1 patient experiencing associated toxicity (grade 3 liver injury). Anakinra may be useful in the management of asHLH provoked by rheumatologic conditions, although its benefit in asHLH provoked by other factors may be limited.

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It is complicated to establish a consensus on the management and diagnosis of malignancy-triggered hemophagocytic lymphohistiocytosis (M-HLH) in children, as an initial presentation of malignancy is complicated. In this paper, we analyze the clinical characteristics and outcomes of eight pediatric patients in which M-HLH was the initial presentation of malignancy. All patients had hematologic malignancies: three subcutaneous panniculitis-like T-cell lymphomas, two acute lymphoblastic leukemias, two anaplastic large cell lymphomas, and a systemic EBV + T-cell lymphoma of childhood. The incidence rate of M-HLH among leukemia and malignant lymphoma patients in our institution was 1.9%. From the initial diagnosis of HLH, the median time taken to be diagnosed as a malignancy was about 1.3 months. The majority of patients received HLH-targeted immunosuppression and/or etoposide at first. The patients' clinical response to treatment for HLH and malignancies were varied. Five out of the eight patients died, one of whom died due to HLH-related cerebral edema after the initiation of chemotherapy. The median overall survival was 1.6 years. In order to improve the survival rate, the early detection of M-HLH, rapid screening for malignancy, and complete control of M-HLH with HLH-directed therapy followed by a thorough response monitoring are required.

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Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening immune activation syndrome that should be recognized earlier for effective treatment. Adults usually have secondary HLH. An uncommon cause of secondary HLH is AIDS and simultaneous opportunistic infections. Acute human immunodeficiency virus (HIV) and opportunistic infections are also independent causes of HLH, so the presence of both should raise suspicion, especially if patients fulfill the criteria. HLH secondary to severe babesiosis is a rare entity as well. Some patients might not meet the full criteria of HLH on presentation, especially when some specific lab test results are still pending. A delay in diagnosis can happen in those cases. Here, we present two cases. The first case is of a 35-year-old homosexual male who presented with constitutional symptoms of one-week duration. He was diagnosed and started on the treatment of HIV. His fever was not resolving and further investigations led to a diagnosis of disseminated histoplasma infection. The patient fulfilled the criteria of HLH as well. Prompt therapy resulted in the improvement of clinical and laboratory parameters. The second case is of a 72-year-old female presenting with fever. A diagnosis of severe babesiosis and secondary HLH was made. Treatment of babesia resulted in the improvement of clinical and biochemical parameters.

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INTRODUCTION: Hemophagocytic lymphohistiocytosis (HLH) is an immune deregulation disorder with varied clinical presentation which clinically overlaps with widespread tropical infections. METHODS: We conducted a retrospective chart review of children diagnosed with HLH at our center from February-2017 to October-2020. RESULTS: Out of the nine diagnosed patients, genetic predisposition was present in three children; two had identified infectious triggers. The mean age of presentation was 30 months with male predominance. The most common clinical findings were fever, organomegaly, and pancytopenia. The median value of fibrinogen was-156 mg/dL, ferritin-12 957 ng/mL and for triglycerides-349 mg/dL, respectively. In children with identified genetic predisposition, serum ferritin levels were usually more than 10 000 ng/mL. The majority of our patients had evidence of hemophagocytosis on bone marrow examination. In our experience, although nonspecific, very high ferritin and serum triglycerides with low fibrinogen in a patient with bi-cytopenia, pancytopenia was the most suggestive evidence of HLH. Genetic evaluation in our series identified three children, one with primary HLH genetic mutation and two with underlying immune deficiency syndrome. The presence of HLH in the accelerated phase of Chediak-Higashi and AD Hyper IgE syndrome with HLH is extremely rare. Leishmaniasis (in nonendemic area) and Ebstein-Barr virus (EBV) was identified as an infectious trigger in two cases. Most of our cases received treatment as per HLH 2004 protocol. Three children died during the initial diagnosis and treatment. HLH with subcutaneous panniculitis-like T-cell lymphoma recovered well. CONCLUSION: HLH remains a life-threatening disorder associated with a variety of underlying illnesses as highlighted by our case series.

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Primary (familial/hereditary) and secondary (non-familial/hereditary) hemophagocytic lymphohistiocytosis (HLH) are hyperinflammatory and hypercytokinemic syndromes. Secondary HLH includes infection- (eg viral/bacterial/fungal/parasitic) and non-infection- (eg collagen disease or malignancy) related diseases. Viral HLH is the major type among all age groups. Secondary viral HLH and primary HLH must be differentiated carefully because primary HLH can be associated with viral infection(s), and the outcome is dismal without a timely diagnosis and hematopoietic stem cell transplantation (HSCT). Epstein-Barr virus (EBV)-related HLH (EBV-HLH) is the most common type of viral HLH in childhood. For non-EBV-HLH, appropriate treatment of viral infection, followed by immunomodulatory agent(s) such as corticosteroids, intravenous immunoglobulin or cyclosporine A, is usually successful; however, recent SARS-CoV-2-related HLH may become life-threatening. EBV-HLH may occur heterogeneously associated with the primary infection, with chronic active EBV infection or with underlying primary HLH. Although immunomodulatory agent(s) are effective in the majority of EBV-HLH cases, management differs from that of non-EBV-HLH because severe and refractory cases may require etoposide-containing HLH-1994/2004 regimens or other experimental agents. The novel agent, emapalumab (an anti-IFN-γ monoclonal antibody) can be used to treat EBV-HLH cases to avoid the risk of secondary malignancy due to etoposide. Finally, HSCT is required for refractory EBV-HLH cases and can also be curative in some other cases.

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Hemophagocytic lymphohistiocytosis (HLH) is a severe systemic inflammatory syndrome that is often fatal. In the adult population, it is believed to develop secondary to immune dysregulation due to rheumatologic, infectious, malignant, and recently, immunomodulatory drugs. It's co-occurrence with phagocytosis by non-macrophage cells has not been previously well defined. We present a case of lenalidomide-associated HLH with concurrent plasma cell hemophagocytosis in a patient with controlled multiple myeloma (MM).