Severe hemophagocytic lymphohistiocytosis in adults-experience from an intensive care unit from North India

Hypofibrinogenemia is an independent predictor of hemophagocytic lymphohistiocytosis in children with sepsis

Hemophagocytic lymphohistiocytosis (HLH) is a potentially life-threatening condition in children with sepsis. We herein aimed to identify clinical and laboratory predictors of HLH in children with sepsis. We conducted a retrospective study of 568 children with sepsis admitted to Guangdong Women and Children Hospital from January 2019 to June 2022. HLH, while rare (6.34%), proved to be a highly fatal complication (37.14%) in children with sepsis. Children with HLH had higher levels of aspartate aminotransferase, lactate dehydrogenase, triglycerides, and ferritin than children without HLH; conversely, they displayed decreased levels of neutrophils, hemoglobin, platelets, fibrinogen, and albumin. Additionally, the HLH group showed higher rates of prolonged fever (> 10 days), hepatomegaly, and splenomegaly than the non-HLH group. Our retrospective analysis identified hypofibrinogenemia (OR = 0.440, P = 0.024) as an independent predictor for the development of HLH in patients with sepsis. The optimal cutoff value for fibrinogen was found to be < 2.43 g/L. The area under the curve for diagnosing HLH was 0.80 (95% confidence interval: 0.73-0.87, P < 0.0001), with a sensitivity of 72.41% and specificity of 76.27%. Thus, hypofibrinogenemia emerges as a potentially valuable predictor for HLH in children with sepsis.

Hemophagocytic Lymphohistiocytosis Associated with Synergistic Defects of AP3B1 and ATM Genes: A Case Report and Literature Review

Hemophagocytic lymphohistiocytosis (HLH) is an overwhelming immune system activation that manifests as hyperinflammation and life-threatening multiple organ failure. However, the clinical manifestations of the systemic inflammatory response in sepsis and fulminant cytokine storm caused by HLH macrophage activation are very similar and difficult to distinguish. HLH triggered by two novel gene defects manifesting with multiorgan dysfunction syndrome (MODS) and distributive shock has not been reported. A 14-year-old male patient was hospitalized with a high fever, his condition deteriorated rapidly, accompanied by cytopenia, shock, and MODS, and he was subsequently transferred to our intensive care unit (ICU) for symptomatic and organ-supportive treatments. Laboratory indicators of cytopenia, hypofibrinogenemia, hypertriglyceridemia, hyperferritinemia, high soluble CD25, low natural killer (NK) cell cytotoxicity, and hemophagocytosis in the bone marrow confirmed the diagnosis of HLH. Molecular genetic analysis revealed that two novel heterozygous gene mutations in AP3B1 (c.3197 C > T) and ATM (c.8077 G > T) might have accounted for the onset. After treatment, the patient’s condition successfully improved. This case report demonstrates the timely determination of underlying triggers and critical care supports (supportive and etiological treatment) of HLH related to the improved outcome.

Etoposide treatment in secondary hemophagocytic syndrome: impact on healthcare-associated infections and survival

Background

Etoposide remains the cornerstone of symptomatic management of critically ill patients with secondary hemophagocytic syndrome (sHS). Risk of healthcare-associated infections (HAIs) in this setting with etoposide has never been assessed. We sought to evaluate the association between etoposide administration, HAIs occurrence and survival in critically ill adult patients with sHS. In this retrospective single-center study conducted in a university hospital ICU between January 2007 and March 2020, all consecutive patients with sHS were included. HAIs were defined as any microbiologically documented infection throughout ICU stay. Competing risk survival analysis was performed to determine factors associated with HAIs. Propensity score-based overlap weighting was performed to adjust for factors associated with etoposide use.

Results

168 patients with a median age of 49 [38, 59] were included. Forty-three (25.6%) patients presented with at least 1 microbiologically documented HAI throughout ICU stay. After adjustment, cumulative incidence of HAI was higher in patients receiving etoposide (p = 0.007), while survival was unaffected by etoposide status (p = 0.824). By multivariable analysis, etoposide treatment was associated with a higher incidence of HAIs (sHR 3.75 [1.05, 6.67]), whereas no association with survival (sHR 0.53 [0.20, 1.98]) was found. Other factors associated with increased mortality after adjustment included age, immunodepression, male sex, SOFA score > 13, and occurrence of HAI.

Conclusions

In patients with sHS, etoposide treatment is independently associated with increased occurrence of HAIs, whereas no association with survival was found. Intensivists should be aware of increased infectious risk, to promptly detect and treat infections in this specific setting. Studies to assess benefits from prophylactic anti-infectious agents in this setting are warranted and the lack of benefit of etoposide on survival needs to be interpreted cautiously.

Haemophagocytic Lymphohistiocytosis with Leptospirosis: A Rare but Devastating Complication

Introduction

Secondary haemophagocytic lymphohistiocytosis (sHLH), often associated with an array of infections, malignancies, and autoimmune diseases, is rarely seen with leptospirosis, which carries a relatively poor prognosis even with modern state-of-the-art medical care. We describe a patient with leptospirosis complicated by sHLH who succumbed to illness following multiorgan dysfunction. Case Description. A 74-year-old farmer presented with high-grade, unsettling fever for a week. Muddy water exposure and suggestive symptoms prompted investigation and management in the line of leptospirosis (IV ceftriaxone was instituted, and later, MAT (microscopic agglutination test) became positive). Subsequently, he developed severe acute hypoxemia requiring mechanical ventilation and acute renal failure requiring renal replacement therapy. Bone marrow biopsy and markedly elevated serum ferritin and triglyceride levels done on day 10 (with unresolving fever, hepatosplenomegaly, and pancytopaenia) confirmed the diagnosis of HLH. The routine cultures, retroviral studies, CMV, dengue, hanta and mycoplasma antibodies, tuberculosis and COVID-19 PCR, and malaria screening were all normal. There was no improvement of hypoxemia following intravenous methylprednisolone. He died on day 15 despite escalating organ support.

Conclusion

Leptospirosis is a common zoonotic disease in the tropics with significant morbidity and mortality. In the case of severe leptospirosis, overlapping clinical features with sHLH make the diagnosis of the latter challenging. No assessment tools are available to date to predict the risk of developing sHLH in a patient having leptospirosis. Outcome following sHLH due to leptospirosis still remains majorly ominous. A high index of suspicion and low threshold for specific investigations could possibly alter the outcome following such an occurrence.

Coagulation disorders in patients with severe hemophagocytic lymphohistiocytosis

Background

Coagulation disorders are common in patients with hemophagocytic lymphohistiocytosis (HLH), associated with an increased risk of bleeding and death. We aim to investigate coagulation disorders and their outcome implications in critically ill patients with HLH.

Methods

We prospectively evaluated 47 critically ill patients with HLH (median age of 54 years [42–67]) between April 2015 and December 2018. Coagulation assessments were performed at day 1. Abnormal standard coagulation was defined as prothrombin time (PT) <50% and/or fibrinogen <2g/L. HLH aetiology was mostly ascribed to haematological malignancies (74% of patients).

Results

Coagulation disorders and severe bleeding events were frequent, occurring in 30 (64%) and 11 (23%) patients respectively. At day 1, median fibrinogen level was 2∙65g/L [1.61–5.66]. Fibrinolytic activity was high as suggested by increased median levels of D-dimers, fibrin monomers, PAI-1 (plasminogen activator inhibitor) and tPA (tissue plasminogen activator). Forty-one (91%) patients had a decreased ADAMTS13 activity (A Disintegrin-like And Metalloproteinase with ThromboSpondin type 1 repeats, member 13). By multivariable analysis, the occurrence of a severe bleeding (OR 3.215 [1.194–8.653], p = 0∙021) and SOFA score (Sepsis-Related Organ Failure Assessment) at day 1 (OR 1.305 per point [1.146–1.485], p<0∙001) were independently associated with hospital mortality. No early biological marker was associated with severe bleeding.

Conclusions

Hyperfibrinolysis may be the primary mechanism responsible for hypofibrinogenemia and may also participate in ADAMTS13 degradation. Targeting the plasmin system appears as a promising approach in severe HLH-related coagulation disorders.

Treatment and Mortality of Hemophagocytic Lymphohistiocytosis in Adult Critically Ill Patients: A Systematic Review With Pooled Analysis

OBJECTIVES

Hemophagocytic lymphohistiocytosis is a cytokine release syndrome caused by uncontrolled immune activation resulting in multiple organ failure and death. In this systematic review, we aimed to analyze triggers, various treatment modalities, and mortality in critically ill adult hemophagocytic lymphohistiocytosis patients.

DATA SOURCES

MEDLINE database (PubMed) at October 20, 2019.

STUDY SELECTION

Studies and case series of patients greater than or equal to 18 years old, of whom at least one had to be diagnosed with hemophagocytic lymphohistiocytosis and admitted to an ICU.

DATA EXTRACTION

Source data of studies and case series were summarized and analyzed on an individual basis. Multivariable logistic regression analysis was performed adjusting for age, sex, and trigger groups. Each single treatment agent was entered as a dichotomous variable to determine treatments associated with survival, regardless if given alone or in combination.

DATA SYNTHESIS

In total, 661 patients from 65 studies and case series were included. Overall mortality was 57.8%. Infections were the most frequent trigger (49.9%), followed by malignancies (28.0%), autoimmune diseases (12.1%), unknown triggers (9.4%), and drugs (0.6%). Treatment with IV immunoglobulins was associated with improved survival (odds ratio, 0.548; 95% CI, 0.337-0.891; p = 0.015), while treatment with cyclosporine was associated with increased risk of death (odds ratio, 7.571; 95% CI, 3.702-15.483; p < 0.001). Considering different trigger groups separately, same results occurred only for infection-triggered hemophagocytic lymphohistiocytosis. No information was available on disease severity and other confounding factors.

CONCLUSIONS

Mortality of hemophagocytic lymphohistiocytosis in the ICU is high. Most common triggers were infections. Results of survival analyses may be biased by treatment indication and disease severity. Future studies prospectively investigating treatment tailored to critically ill hemophagocytic lymphohistiocytosis patients are highly warranted.

A case report of idiopathic Hemophagocytic lymphohistiocytosis in an immunocompetent adult

Hemophagocytic lymphohistiocytosis poses a diagnostic dilemma due to the absence of specific clinical and laboratory findings, especially in adults. Despite greater recognition of the disease, secondary idiopathic forms are still reported.

Hemophagocytic Lymphohistiocytosis in the Medical ICU: A Single-Institution Cohort Study on Acute Liver Failure and Mortality

Hemophagocytic lymphohistiocytosis is a life-threatening hyperinflammatory disorder that is associated with high morbidity and mortality in the ICU. It has also been associated with acute liver failure.

DESIGN

Retrospective observational study.

SETTING

Tertiary-care medical ICU.

PATIENTS

Thirty-one patients critically ill with hemophagocytic lymphohistiocytosis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We performed a comprehensive review of critically ill hemophagocytic lymphohistiocytosis patients admitted to a tertiary-care medical ICU from January 2012 to December 2018. Most patients presented with constitutional symptoms and elevated liver enzymes and thrombocytopenia were common upon hospital admission. ICU admission laboratory and clinical variables were used to calculate Acute Physiology and Chronic Health Evaluation II, hemophagocytic syndrome diagnostic score, and model for end-stage liver disease. Mean age of the cohort was 48.1 years, and 45% were male. The mortality rate was 65% at 28 days and 77% at 1 year. About 28-day survivors were younger, had lower mean Acute Physiology and Chronic Health Evaluation II score (16.5 vs 23.0; p = 0.004), and higher mean hemophagocytic syndrome diagnostic score (249.1 vs 226.0; p = 0.032) compared with nonsurvivors. Survivors were less likely to receive mechanical ventilation, renal replacement therapy, or vasopressor support and were more likely to receive chemotherapy for hemophagocytic lymphohistiocytosis. In this ICU cohort, 29% were diagnosed with acute liver failure, of whom only 22% developed acute liver failure early during their hospital stay. Acute liver failure was associated with a higher model for end-stage liver disease score upon hospital admission. Available histology in those that developed acute liver failure showed massive hepatic necrosis, or histiocytic or lymphocytic infiltrates.

CONCLUSIONS

Patients admitted to the ICU with hemophagocytic lymphohistiocytosis have a high mortality. Those who survived had lower Acute Physiology and Chronic Health Evaluation scores, had higher hemophagocytic syndrome diagnostic scores, are more likely to receive hemophagocytic lymphohistiocytosis specific chemotherapy, and are less likely to have organ failure. Hemophagocytic lymphohistiocytosis can be associated with acute liver failure especially when model for end-stage liver disease score is elevated upon admission.

Coagulation Disorders in Hemophagocytic Lymphohistiocytosis/Macrophage Activation Syndrome

Hemophagocytic lymphohistiocytosis (HLH) is a rare and severe condition that can lead patients to the intensive care unit. HLH diagnosis may be challenging, as it relies on sets of aspecific criteria. Several organ dysfunctions have been described during HLH, including hemostasis impairment found in more than half of the patients. The most frequently reported anomaly is a decrease in the fibrinogen level, which has been associated with higher mortality rates. Coagulation impairment study in patients with HLH represents an interesting field of research, as little is known about the mechanism leading to hypofibrinogenemia.

Challenges in the diagnosis of hemophagocytic lymphohistiocytosis: Recommendations from the North American Consortium for Histiocytosis (NACHO)

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of pathologic immune activation, often associated with genetic defects of lymphocyte cytotoxicity. Though a distinctive constellation of features has been described for HLH, diagnosis remains challenging as patients have diverse presentations associated with a variety of triggers. We propose two concepts to clarify how HLH is diagnosed and treated: within the broader syndrome of HLH, "HLH disease" should be distinguished from "HLH disease mimics" and HLH subtypes should be categorized by specific etiologic associations, not the ambiguous dichotomy of "primary" and "secondary." We provide expert-based advice regarding the diagnosis and initiation of treatment for patients with HLH, rooted in improved understanding of its pathophysiology.

Recommendations for the management of hemophagocytic lymphohistiocytosis in adults

Hemophagocytic lymphohistiocytosis (HLH) is a severe hyperinflammatory syndrome induced by aberrantly activated macrophages and cytotoxic T cells. The primary (genetic) form, caused by mutations affecting lymphocyte cytotoxicity and immune regulation, is most common in children, whereas the secondary (acquired) form is most frequent in adults. Secondary HLH is commonly triggered by infections or malignancies but may also be induced by autoinflammatory/autoimmune disorders, in which case it is called macrophage activation syndrome (MAS; or MAS-HLH). Most information on the diagnosis and treatment of HLH comes from the pediatric literature. Although helpful in some adult cases, this raises several challenges. For example, the HLH-2004 diagnostic criteria developed for children are commonly applied but are not validated for adults. Another challenge in HLH diagnosis is that patients may present with a phenotype indistinguishable from sepsis or multiple organ dysfunction syndrome. Treatment algorithms targeting hyperinflammation are frequently based on pediatric protocols, such as HLH-94 and HLH-2004, which may result in overtreatment and unnecessary toxicity in adults. Therefore, dose reductions, individualized tailoring of treatment duration, and an age-dependent modified diagnostic approach are to be considered. Here, we present expert opinions derived from an interdisciplinary working group on adult HLH, sponsored by the Histiocyte Society, to facilitate knowledge transfer between physicians caring for pediatric and adult patients with HLH, with the aim to improve the outcome for adult patients affected by HLH.

Intensive care unit complications and outcomes of adult patients with hemophagocytic lymphohistiocytosis: A retrospective study of 16 cases

AIM

To study the management, complications and outcomes of adult patients admitted with hemophagocytic lymphohistiocytosis (HLH) in the intensive care unit (ICU).

METHODS

We performed a retrospective observational study of adult patients with the diagnosis of “HLH” admitted to the two academic medical ICUs of Baylor College of Medicine between 01/01/2013 to 06/30/2017. HLH was diagnosed using the HLH-2004 criteria proposed by the Histiocyte Society.

RESULTS

Sixteen adult cases of HLH were admitted to the medical ICUs over 4 years. Median age of presentation was 49 years and 10 (63%) were males. Median Sequential Organ Failure Assessment (SOFA) score at the time of ICU admission was 10. Median ICU length of stay (LOS) was 11.5 d and median hospital LOS was 29 d. Septic shock and acute respiratory failure accounted for majority of diagnoses necessitating ICU admission. Septic shock was the most common ICU complication seen in (88%) patients, followed by acute kidney injury (81%) and acute respiratory failure requiring mechanical ventilation (75%). Nine patients (56%) developed disseminated intravascular coagulation and eight (50%) had acute liver failure. 10 episodes of clinically significant bleeding were observed. Multi system organ failure was the most common cause of death seen in 12 (75%) patients. The 30 d mortality was 37% (6 cases) and 90 d mortality was 81% (13 cases). There was no difference in mortality based on age (above or less than 50 years), SOFA score on ICU admission (more than or less than 10), immunosuppression, time to diagnose HLH or direct ICU admission versus floor transfer.

CONCLUSION

HLH is a devastating disease associated with poor outcomes in ICU. Intensivists need to have a high degree of clinical suspicion for HLH in patients with septic shock/multi system organ failure and progressive bi/pancytopenia who are not responding to standard management in ICU.

[Hemophagocytic lymphohistiocytosis : A diagnostic challenge on the ICU]

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) has well been studied as a genetic disorder in children (primary HLH). Mutations in the regulatory complex of the cellular immune synapse lead to a loss of function of cytotoxic T‑cells and natural killer cells with excessive inflammation based on a cytokine storm. During the last decade, an increasing number of adult HLH patients without a family history of HLH (secondary or acquired HLH) have been reported. Various triggers - infections, malignancies or autoimmune diseases - result in an acquired loss of function of these cells and a sepsis-like disease. Missed or late diagnosis is believed to be a major cause of the high mortality.

OBJECTIVES

To describe the current knowledge on HLH and to raise awareness.

MATERIALS AND METHODS

Analysis of case reports, current studies, and expert recommendations.

RESULTS

Increased vigilance in identifying the adult form of HLH resulted in an increasing number of case reports over the past few years. HLH patients typically present with a clinical phenotype resembling severe sepsis or septic shock with fever, cytopenia, and organomegaly, which do not or insufficiently respond to anti-infective treatment. Early recognition of HLH distinction from sepsis, and prompt initiation of treatment - which is fundamentally different from sepsis - are crucial for improved outcome. A promising diagnostic parameter is ferritin, which has gained sufficient specificity, but only in the context of the triad of fever, cytopenia, and organomegaly. Treatment of adult HLH patients requires immunosuppression, with strict therapeutic guidance derived from the triggering disease.

CONCLUSIONS

Because of the similar clinical presentation to that of sepsis, HLH is often not recognized, resulting in a fatal outcome. In "sepsis" patients on the ICU with deterioration despite a standard of care, HLH needs to be considered by testing for ferritin when considering differential diagnoses. The complexity of the illness requires interdisciplinary patient care with specific integration of the hematologist in the diagnostic workup and therapeutic management, because of the frequent use of chemotherapy-based immunosuppression.

ITK Gene Mutation: Effect on Survival of Children with Severe Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is characterized by deadly hyperinflammatory syndrome, but data on severe HLH with multi-organ dysfunction in children are scant. The authors report a retrospective study of 8 cases with severe HLH from a pediatric intensive care unit (PICU) over a 1-y period and found that Epstein barr virus (EBV) -infection was the most common etiology. All patients had genetic analysis, which showed that four patients with EBV -infection had one homozygous mutation, c.985+75G>A (at position chr5:156667232) in exon10 of the ITK gene with poor survival rates. ITK ⁺ mutation group had higher percentages of CD3⁺CD8⁺ T cells (36.0 ± 8.4 %) than those in ITK ^- mutation group (28.8 ± 5.5 %), while they had similar levels of CD3⁺CD4⁺ T cells. ITK ⁺ mutation group had lower proportion of CD3^-CD19⁺ B cells (16.3 ± 2.9 %) and CD16⁺CD56⁺ NK cells (8.4 ± 2.6 %) than ITK ^- mutation group (29.6 ± 5.1 % and 15.9 ± 9.0 % respectively). Most importantly, patients with EBV infection with c.985+75G>A mutation in ITK had lower survival rates than ITK ^- mutation group which it may be related with cellular immune dysfunction.

Stuck with pancytopenia in dengue fever: Evoke for hemophagocytic syndrome

The hemophagocytic syndrome is an atypical and rare manifestation of dengue fever (DF). We describe a 15-year-old girl developing DF associated hemophagocytic syndrome who responded with supportive treatment.

Coagulation Disorders and Bleedings in Critically Ill Patients With Hemophagocytic Lymphohistiocytosis

Reactive hemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition related to a cytokine storm leading to multiorgan dysfunction. A better understanding of coagulation disorders, frequently reported in HLH patients, may improve outcomes. Critically ill HLH patients managed in a multidisciplinary national reference center were retrospectively included. Relationships between coagulation disorders, severe bleedings, and outcomes were assessed. One hundred and seventeen patients fulfilled the HLH 2004 criteria. The most common HLH etiology was hematologic conditions (73%), followed by infectious diseases (20%), systemic rheumatic diseases (5%), and undetermined HLH etiology (3%). All patients exerted thrombocytopenia. Coagulation disorders were diagnosed in 79 (68%) patients (61 had hypofibrinogenemia < 1.5 g/L, 51 had prothrombin time [PT]  <  0%). The worst median value throughout ICU stay was 52% (38-65) for PT with a factor V level of 35% (27-43), 1.59 (1.30-2.09) for the activated partial thromboplastin time (APTT) ratio, and 2.33 g/L (1.13-3.86) for the fibrinogen level. Disseminated intravascular coagulation (DIC) was found in 50% of patients. Coagulation disorders were more frequent in immunocompromised patients, those with histological/cytological feature of hemophagocytosis, those with the highest ferritin concentrations, and in patients with HLH not related to infection. These patients were more prone to receive mechanical ventilation, vasopressors, or renal replacement therapy. Twenty-six (22%) patients presented severe bleeding complications, including 5 patients dying from hemorrhagic shock. Strikingly, the only coagulation parameter significantly associated with severe bleeding was low fibrinogen with a cutoff value of 2 g/L (P = 0.03). Overall, 33 (28%) patients died in the ICU and hospital mortality was 44%. Coagulation disorders were associated with higher mortality, especially fibrinogen < 2 g/L (P = 0.04) and PT value (P = 0.03). The occurrence of bleeding complications was not associated with higher risk of hospital death. Risk factors associated with mortality by multivariate analysis were fibrinogen level < 2 g/L (OR 2.42 [1.08-5.41]), SOFA score > 6 (OR 3.04 [1.32-6.98]), and age > 46 years (OR 2.26 [1.02-5.04]). Up to two-third of critically ill HLH patients present with coagulation disorders. Hypofibrinogenemia or DIC was found in half of the patients and low PT in 40%. These patients require more life support and have a higher mortality rate. Fibrinogen < 2 g/L is associated with the occurrence of severe bleeding and mortality.

Hemophagocytic lymphohistiocytosis secondary to infections: a tropical experience!

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal hyper inflammatory condition, if not recognized and treated in time. A high index of suspicion can help identify the condition early. This condition can occur in the primary or secondary form. Secondary HLH or hemophagocytic syndrome (HPS) secondary to infections is an important clinical entity especially in tropical world. In this article, we share our experience with this entity and make an attempt to explore literature about ravenous macrophages which occurs secondary to infections. It is a series of six cases of HLH secondary to infectious disease in our center in a coastal city in South India over last one year with follow up.

Hemophagocytic Syndrome and Critical Illness: New Insights into Diagnosis and Management

Hemophagocytic lymphohistiocytosis (HLH) comprises a heterogeneous group of diseases that are characterized by a hyperinflammatory state due to uncontrolled T cell, macrophage, and histiocyte activation, accompanied by excessive cytokine production. This rare condition is almost uniformly fatal unless promptly recognized and treated. Much progress has been made in the last two decades in our understanding of the mechanisms underlying familial, and to a lesser extent, acquired cases of HLH. Recurrent mutations in more than 10 different genes have now been identified, involving biological pathways converging on intracellular vesicle trafficking and cytolytic granule exocytosis. Mechanisms underlying the majority of patients with acquired HLH, however, remain elusive, hampering both diagnostic evaluation and therapeutic management of these patients. Given that the majority of intensive care unit (ICU) patients with sepsis or multiorgan failure share many features of HLH, it is especially critical for pediatric and adult intensivists to be able to recognize patients with bona fide HLH and initiate treatment without delay. In this article, we review our current understanding of the pathophysiology, clinical testing, diagnosis, and treatment of patients with HLH, especially as it pertains to the care of critically ill patients in pediatric and medical ICUs.