Secondary hemophagocytic lymphohistiocytosis versus cytokine release syndrome in severe COVID-19 patients

Macrophage Activation Syndrome in Viral Sepsis

Macrophage activation syndrome (MAS) is a life-threatening systemic hyperinflammatory syndrome triggered by various infections, particularly viral infections, autoimmune disorders, and malignancy. The condition is characterized by an increased production of proinflammatory cytokines resulting in a cytokine storm and has been associated with poor clinical outcomes. During the COVID-19 pandemic, patients with severe manifestations developed features similar to those of MAS, although these characteristics remained well defined within the lung. Additionally, other viral infections including EBV, the herpes family of viruses, hepatitis viruses, influenza, HIV, and hemorrhagic fevers can be complicated by MAS. The diagnosis and management of the condition remain challenging due to the lack of consensus on specific guidelines, especially among the adult population. Currently, therapeutic options primarily rely on medications that are typically used to treat primary hemophagocytic lymphohistiocytosis, such as corticosteroids and etoposide. In addition, cytokine-targeted therapies present promising treatment options. The objective of this review is to discuss the emergence of MAS in the context of viral infections including, but not limited to, its occurrence in COVID-19.

Exploring the Correlation Between Splenomegaly and Lung Involvement in COVID-19: A Retrospective Study

Background Coronavirus disease 2019 (COVID-19), resulting from the severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), has not only shown substantial effects on the respiratory system but also on extrapulmonary systems, including cardiovascular, gastrointestinal, hematological, and immune responses, notably spleen enlargement. The connection between the enlargement of the spleen and pulmonary complications in individuals with COVID-19 is still not well elucidated, with current studies offering divergent conclusions. Objective This study aims to elucidate the correlation between splenomegaly, as assessed by computed tomography (CT) imaging, and the extent of lung involvement (LI) in COVID-19 patients, thereby offering insights into potential prognostic indicators. Methodology A hospital-based, cross-sectional, retrospective study was conducted involving 1058 symptomatic COVID-19 patients confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR), aged 18 years and above. CT imaging was utilized to evaluate spleen size and LI. Statistical analyses, including Pearson correlation and simple linear regression, were performed to explore the relationship between spleen size and LI. Results The study cohort exhibited a mean spleen size of 9.49 cm and a mean LI score of 0.272. The Pearson correlation coefficient was calculated at 0.0495, indicating a marginal positive correlation between spleen size and LI. Regression analysis demonstrated a minimal impact of spleen size on LI, with spleen size accounting for only 0.2% of the variance in LI scores. Conclusions The study found a slight, statistically non-significant correlation between splenomegaly and LI in COVID-19 patients, suggesting that while splenic enlargement may reflect systemic disease involvement, it is not a strong independent predictor of lung damage extent. The findings highlight the complexity of extrapulmonary manifestations and highlight the need for additional research to fully understand the implications of splenic involvement in COVID-19.

Severe Cytokine Release Syndrome and Hemophagocytic Lymphohistiocytosis (HLH)-Like Syndrome Following Administration of Combined Brentuximab Vedotin and Nivolumab for Recurrent Classical Hodgkin Lymphoma: A Case Report

Brentuximab vedotin (BV) and nivolumab are increasingly utilized as a novel regimen in patients with relapsed/refractory classical Hodgkin lymphoma (cHL). A 26-year-old male presented to the hospital with refractory diabetic ketoacidosis and multiple electrolyte abnormalities, 9 days after the first dose of brentuximab vedotin and nivolumab for recurrent classical Hodgkin lymphoma. During his hospitalization, he developed multi-organ failure. His workup showed elevated cytokine levels concerning severe cytokine release syndrome (CRS) and hemophagocytic lymphohistiocytosis (HLH)-like syndrome. Despite treatment with CRS- and HLH-directed therapies, his clinical status deteriorated due to ongoing multifactorial shock and worsening multi-organ dysfunction, and comfort care measures were eventually pursued. To our knowledge, there have been no other cases reported of HLH-like syndrome after the combination of BV and nivolumab in patients with cHL. This case of a fatal adverse event following one dose of BV and nivolumab underscores the vital need for close monitoring of patients receiving this treatment regimen.

COVID-19 Pneumonia and Cytokine Storm Syndrome

Virus-associated cytokine storm syndrome (CSS) has been recognized for a long time and the classic viruses associated are the herpes viruses EBV, CMV, and HHV-8 as described in chapters IVa,b. In addition, pandemic viruses such as influenza, SARS, and MERS can result in severe CSS that might ultimately lead to severe acute respiratory distress syndrome (ARDS) and death [1-3]. A new pandemic caused by SARS-CoV-2 that started in 2019 has defined another chapter in the virus-associated CSS. The clinical spectrum of SARS-CoV-2 infection has many faces. In most people, it will be asymptomatic, but it can also result in severe COVID-19 pneumonia, ARDS, and multiorgan failure depending on age, comorbidities, and immune status [4]. In addition, this pandemic has known many different stages and developed in a unique way in the first 2 years. It started in a setting where there was no immunity to the virus and after a year, highly effective vaccines were introduced and herd immunity built up over time. However, vaccine effectiveness was waning over time depending on multiple factors, and novel variant strains of the virus circulated across different areas in the world. Antiviral therapy was developed and introduced, and treatment changed from giving no immunomodulatory treatment, followed by the introduction of corticosteroids [5], and later the addition of more targeted strategies such as JAK inhibitors [6] and blocking IL-6 signaling [7]. Therefore, the scientific literature published on COVID-19 must be seen in the context of a highly dynamic and rapidly changing pandemic, making it difficult to compare results from early studies to more recent reports even within 2 years. Still, a lot has been learned over a very short period. It has become apparent that severe COVID-19 is predominantly a disease of immune dysregulation with components that can be defined as CSS. It has unique features and overlapping characteristics with other CSSs, and immunological treatment addressing the CSS has been extensively explored, which will be described here.

A case of hemophagocytic lymphohistiocytosis in a hemodialysis patient with coronavirus disease 2019

During the treatment of a patient on hemodialysis with severe coronavirus disease 2019 (COVID-19), the patient was weaned from extracorporeal membrane oxygenation, which was used to treat severe COVID-19 pneumonia. However, the patient's condition worsened after the peak infection phase of COVID-19 because of acute respiratory distress syndrome with suspected hemophagocytic lymphohistiocytosis (HLH). After a bone marrow biopsy confirmed the diagnosis, methylprednisolone pulse therapy, followed by combination therapy (including oral prednisolone and cyclosporine) was immediately administered, and the patient survived. Because HLH can occur a month or more after the onset of COVID-19, even if the viral load is reduced to the point of being undetectable by reverse transcriptase-polymerase chain reaction, it can be considered to correspond to the "post-acute COVID-19 syndrome," which has recently been proposed. Early intervention is necessary, because HLH can be fatal. Therefore, it is important to know that HLH can occur at any stage of COVID-19 and to pay attention to the patient's progress over time, including checking the HScore.

Secondary hemophagocytic lymphohistiocytosis in children (Review)

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.

Bone marrow alterations in COVID-19 infection: The root of hematological problems

INTRODUCTION

The 2019 coronavirus disease (COVID-19) is a respiratory infection caused by the SARS-CoV-2 virus with a significant impact on the hematopoietic system and homeostasis. The effect of the virus on blood cells indicates the involvement of the bone marrow (BM) as the place of production and maturation of these cells by the virus and it reminds the necessity of investigating the effect of the virus on the bone marrow.

METHOD

To investigate the effects of COVID-19 infection in BM, we reviewed literature from the Google Scholar search engine and PubMed database up to 2022 using the terms "COVID-19; SARS-CoV-2; Bone marrow; Thrombocytopenia; Hemophagocytosis; Pancytopenia and Thrombocytopenia.

RESULTS

Infection with the SARS-CoV-2 virus is accompanied by alterations such as single-line cytopenia, pancytopenia, hemophagocytosis, and BM necrosis. The presence of factors such as cytokine release syndrome, the direct effect of the virus on cells through different receptors, and the side effects of current treatments such as corticosteroids are some of the important mechanisms in the occurrence of these alterations.

CONCLUSION

To our knowledge, this review is the first study to comprehensively investigate BM alterations caused by SAR-CoV-2 virus infection. The available findings show that the significant impact of this viral infection on blood cells and the clinical consequences resulting from them are deeper than previously thought and it may be rooted in the changes that the virus causes in the BM of patients.

Hemophagocytic Syndrome and COVID-19: A Comprehensive Review

Hemophagocytic lymphohistiocytosis (HLH), a hyperinflammatory hyperferritinemic syndrome, is triggered by various etiologies and diseases and can lead to multiorgan dysfunction and death. There are two types of HLH: primary and secondary. Primary HLH (pHLH) is caused by a genetic mutation resulting in dysfunction in cytotoxic T lymphocytes (CTLs), natural killer (NK) cells, hyperactivated immune cells, and hypercytokinemia. In secondary HLH (sHLH), an underlying etiology is the cause of the disease. Infections, malignancy, and autoimmune diseases are well-known triggers for sHLH. Infectious triggers for sHLH are most frequently viruses, where different mechanisms, including dysregulated CTLs and NK cell activity and persistent immune system stimulation, have been reported. Similarly, in severe coronavirus disease 2019 (COVID-19) patients, a hyperinflammatory mechanism leading to hypercytokinemia and hyperferritinemia has been demonstrated. A similar dysfunction in CTLs and NK cells, persistent immune system stimulation with increased cytokines production, and severe end-organ damage have been reported. Therefore, a significant overlap is present between the clinical and laboratory features seen in COVID-19 and sHLH. However, SARS-CoV-2, similar to other viruses, can trigger sHLH. Hence, a diagnostic approach is needed in severe COVID-19 patients presenting with multiorgan failure, in whom sHLH should be considered.

A Review of Current and Emerging Therapeutic Options for Hemophagocytic Lymphohistiocytosis

Objective:

To provide an overview of clinical sequelae and emerging treatment options for hemophagocytic lymphohistiocytosis (HLH).

Data Sources:

A literature search was conducted using the search terms “hemophagocytic lymphohistiocytosis,” “hemophagocytic syndrome,” “macrophage activation syndrome,” and “treatment” on Ovid and PubMed from January 1, 2017, through September 28, 2022.

Study Selection and Data Extraction:

Relevant clinical trials, meta-analyses, case reports, review articles, package inserts, and guidelines to identify current and emerging therapeutic options for the management of HLH.

Data Synthesis:

Genetic disorders and secondary causes may trigger HLH in both children and adults. Notable improvements in the diagnosis of HLH were seen with implementation of the HLH-2004 standard diagnostic criteria; however, timely and accurate identification of HLH remain significant barriers to optimal management. Multiagent immunochemotherapy are the backbone of aggressive therapy for acutely ill patients with HLH.

Relevance to Patient Care and Clinical Practice:

The global coronavirus 2019 (COVID-19) pandemic and emerging immune effector cell therapies have served to highlight the concerns with immune dysregulation and subsequent HLH precipitation. Without prompt identification and treatment, HLH can be fatal. Historically, the clinician’s armamentarium for managing HLH was sparse, with etoposide-based protocols serving as the standard of care. Relapsed or refractory disease portends a poor prognosis and requires additional treatment options. Second- or subsequent-line options now include hematopoietic stem cell transplantation, emapalumab, alemtuzumab, anakinra, ruxolitinib, and tocilizumab.

Conclusions:

Improvements in diagnostic methods and novel immunosuppressive treatment strategies, including noncytotoxic immunochemotherapy, have transformed the therapeutic landscape. Unfortunately, many unanswered questions remain. Additional studies are required to optimize dosing, schedules, treatment sequences, and indications for novel treatment options.

Enigma of COVID-19: is “multisystem inflammatory syndrome in adults” (MIS-A) predictable?

Background

Severe inflammation and one or more extrapulmonary organ dysfunctions have been reported and this clinical picture is defined as "multisystem inflammatory syndrome in adults" (MIS-A) in severe coronavirus disease-2019 (COVID-19). We aimed to determine the effect of LDH/lymphocyte ratio (LLR) on the development of MIS-A.

Methods

The data of 2333 patients were retrospectively analyzed.

Results

MIS-A rate was found to be 9.9% and MIS-A related mortality was 35.3%. LRR level above 0.24 was found to predict MIS-A development with 70% sensitivity and 65.2% specificity. The risk of MIS-A development was found to be 3.64 times higher in those with LRR levels above 0.24 compared to those with 0.24 and below. In patients with MIS-A, LRR level above 0.32 predicts mortality with 78% sensitivity and 70% specificity.

Conclusions

Early detection of MIS-A with high sensitivity and specificity in a practical ratio is very important in terms new studies.

6-Mercaptopurine and Macrophage Activation Syndrome Case Report and Review of the Literature

Macrophage activation syndrome is a life-threatening syndrome of uncontrolled immune activation with variable clinical presentation making early diagnosis difficult. It is often manifested by the development of multi-organ failure due to systemic inflammatory response. Patients with ulcerative colitis (UC) on purine antimetabolites are at high risk for severe myelosuppression due to the mechanism of thiopurine toxicity which potentially contributes to the development of macrophage activation syndrome. We present a case of a 39-year-old woman with a 2-year history of UC previously treated with 6-mercaptopurine (6-MP) and recent COVID-19 infection, who was admitted to our emergency department for C. difficile infection and subsequently developed macrophage activation syndrome. This case report also raises the question of whether abrupt discontinuation of 6-MP may have contributed to the worsening of the patient's symptoms of underlying hemophagocytic lymphohistiocytosis (HLH) and her rapid deterioration. Both macrophage activation syndrome and COVID-19 infection can produce a large number of pro-inflammatory cytokines termed "cytokine storm," but a pro-inflammatory cytokine panel breakdown helps to differentiate between the two. Our case report emphasizes the importance of close monitoring of patients on purine antimetabolite therapy who present with signs and symptoms of systemic toxicity.

Is COVID-19-associated cytokine storm distinct from non-COVID-19 secondary hemophagocytic lymphohistiocytosis?

Cytokine storm is an umbrella term that describes an inflammatory syndrome characterized by elevated levels of circulating cytokines and hyperactivation of innate and/or adaptive immune cells. One type of cytokine storm is hemophagocytic lymphohistiocytosis (HLH), which can be either primary or secondary. Severe COVID-19-associated pneumonia and acute respiratory distress syndrome (ARDS) can also lead to cytokine storm/cytokine release syndrome (CS/CRS) and, more rarely, meet criteria for the diagnosis of secondary HLH. Here, we review the immunobiology of primary and secondary HLH and examine whether COVID-19-associated CS/CRS can be discriminated from non-COVID-19 secondary HLH. Finally, we review differences in immunobiology between these different entities, which may inform both clinical diagnosis and treatment of patients.

Assessment of the HScore as a predictor of disease outcome in patients with COVID-19

Severe coronavirus disease 2019 (COVID-19) accompanies hypercytokinemia, similar to secondary hemophagocytic lymphohistiocytosis (sHLH). We aimed to find if HScore could predict disease severity in COVID-19. HScore was calculated in hospitalized children and adult patients with a proven diagnosis of COVID-19. The need for intensive care unit (ICU), hospital length of stay (LOS), and in-hospital mortality were recorded. The median HScore was 43.0 (IQR 0.0–63.0), which was higher in those who needed ICU care (59.7, 95% CI 46.4–72.7) compared to those admitted to non-ICU medical wards (38.8, 95% CI 32.2–45.4; P = 0.003). It was also significantly higher in patients who died of COVID-19 (105.1, 95% CI 53.7–156.5) than individuals who survived (41.5, 95% CI 35.8–47.1; P = 0.005). Multivariable logistic regression analysis revealed that higher HScore was associated with a higher risk of ICU admission (adjusted OR = 4.93, 95% CI 1.5–16.17, P = 0.008). The risk of death increased by 20% for every ten units increase in HScore (adjusted OR 1.02, 95% CI 1.00–1.04, P = 0.009). Time to discharge was statistically longer in high HScore levels than low levels (HR = 0.41, 95% CI 0.24–0.69). HScore is much lower in patients with severe COVID-19 than sHLH. Higher HScore is associated with more ICU admission, more extended hospitalization, and a higher mortality rate. A modified HScore with a new cut-off seems more practical in predicting disease severity in patients with severe COVID-19.

Cytokine Storms in the Course of COVID-19 and Haemophagocytic Lymphohistiocytosis in Pregnant and Postpartum Women

The term 'cytokine storm' (CS) applies to a pathological autoimmune reaction when the interactions that lead to cytokine production are destabilised and may even lead to death. CS may be induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In this study, we present our analysis of certain pathological processes that induce a CS in pregnant and postpartum women. We draw our attention to the similarities between the severe course of Coronavirus Disease 2019 (COVID-19) and haemophagocytic lymphohistiocytosis (HLH). It is noteworthy that many of the criteria used to diagnose HLH are described as COVID-19 mortality predictors. Cytokine storms are considered to be an important cause of death in patients with the severe course of SARS-CoV-2 infection. Due to the fact that pregnant women are in an immunosuppressive state, viral pulmonary infections are more perilous for them-possible risks include miscarriage, intrauterine growth restriction or birth before the term; sometimes ventilation support is needed. HLH should be considered in pregnant and puerperal women suffering from moderately severe to severe COVID-19 and presenting with: fever unresponsive to antibiotic therapy, cytopenia, hepatitis and hyperferritinaemia. The HLH disorder is rare and difficult to diagnose; however, its early detection could reduce patient mortality.

Donor-derived ehrlichiosis: two clusters following solid organ transplantation

Ehrlichiosis has been infrequently described as transmissible through organ transplantation. Two donor derived clusters of ehrlichiosis are described here. During the summer of 2020, two cases of ehrlichiosis were reported to the Organ Procurement and Transplantation Network (OPTN) and the Centers for Disease Control and Prevention (CDC) for investigation. Additional transplant centers were contacted to investigate similar illness in other recipients and samples were sent to CDC. Two kidney recipients from a common donor developed fatal ehrlichiosis-induced hemophagocytic lymphocytic histiocytosis (HLH). Two kidney recipients and a liver recipient from another common donor developed ehrlichiosis. All three were successfully treated. Clinicians should consider donor-derived ehrlichiosis when evaluating recipients with fever early after transplantation after more common causes are ruled out, especially if the donor has epidemiological risk factors for infection. Suspected cases should be reported to the organ procurement organization (OPO) and the OPTN for further investigation by public health authorities.

A Comparison of the Clinical, Viral, Pathologic, and Immunologic Features of Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and Coronavirus 2019 (COVID-19) Diseases

CONTEXT

-The purpose of this review is to compare three coronavirus diseases: severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and coronavirus disease 2019 (COVID-19) caused by SARS-CoV, MERS-CoV, and SARS-CoV-2 viruses, respectively.

OBJECTIVE

-To cover the following topics: clinical considerations, viral characteristics, pathology, immune response, pathogenesis, and the prognosis associated with each coronavirus human disease in humans.

DATA SOURCES

-Clinically, flu-like symptoms are usual at the time of presentation for all 3 diseases, but these vary from asymptomatic to severe multi-system involvement. The pathology associated with symptomatic SARS and COVID-19 has been well described, the most prominent of which is diffuse alveolar damage (DAD). The immune response to each of these viruses is highly complex and includes both humoral and cellular components that can have a significant impact on prognosis. In severe cases of COVID-19, a dysregulated innate host immune system can initiate a hyperinflammatory syndrome dominated by endothelial dysfunction that can lead to a hypercoagulable state with microthrombi, resulting in a systemic micro- and macro-vascular disease.

CONCLUSIONS

-The SARS and MERS epidemics have been limited, involving 7,500 and 2,500 individuals, respectively. In contrast, COVID-19 has resulted in a worldwide pandemic with over 177 million cases and 3.9 million deaths as of June 15, 2021, and fatality rates ranging from <0.1% to ~10% depending upon the country. Ending on a positive note, the development of a number of vaccines, at least six of which now are in clinical use, should mitigate and eventually control the devastating COVID-19 pandemic.

The Perfect Cytokine Storm: Utilization of Lung Ultrasound During Urgent Surgery in an Infant With Multisystem Inflammatory Syndrome in Children and Hemophagocytic Lymphohistiocytosis

Reports of children with a temporal association to severe acute respiratory syndrome coronavirus-2 hospitalized with cardiogenic shock or Kawasaki-like disease began emerging in April 2020. In May 2020, the Centers for Disease Control and Prevention published the criteria for what came to be known as multisystem inflammatory syndrome in children, a postinfectious inflammatory immune response to coronavirus disease 2019 exposure. Hemophagocytic lymphohistiocytosis is a heterogeneous disease state associated with systemic hyperinflammation secondary to immune dysregulation. We describe the utility of perioperative lung ultrasound in an infant with both disease states.

Plasmacytoid Dendritic Cells Depletion and Elevation of IFN-γ Dependent Chemokines CXCL9 and CXCL10 in Children With Multisystem Inflammatory Syndrome

Background

SARS-CoV-2 occurs in the majority of children as COVID-19, without symptoms or with a paucisymptomatic respiratory syndrome, but a small proportion of children develop the systemic Multi Inflammatory Syndrome (MIS-C), characterized by persistent fever and systemic hyperinflammation, with some clinical features resembling Kawasaki Disease (KD).

Objective

With this study we aimed to shed new light on the pathogenesis of these two SARS-CoV-2-related clinical manifestations.

Methods

We investigated lymphocyte and dendritic cells subsets, chemokine/cytokine profiles and evaluated the neutrophil activity mediators, myeloperoxidase (MPO), and reactive oxygen species (ROS), in 10 children with COVID-19 and 9 with MIS-C at the time of hospital admission.

Results

Patients with MIS-C showed higher plasma levels of C reactive protein (CRP), MPO, IL-6, and of the pro-inflammatory chemokines CXCL8 and CCL2 than COVID-19 children. In addition, they displayed higher levels of the chemokines CXCL9 and CXCL10, mainly induced by IFN-γ. By contrast, we detected IFN-α in plasma of children with COVID-19, but not in patients with MIS-C. This observation was consistent with the increase of ISG15 and IFIT1 mRNAs in cells of COVID-19 patients, while ISG15 and IFIT1 mRNA were detected in MIS-C at levels comparable to healthy controls. Moreover, quantification of the number of plasmacytoid dendritic cells (pDCs), which constitute the main source of IFN-α, showed profound depletion of this subset in MIS-C, but not in COVID-19.

Conclusions

Our results show a pattern of immune response which is suggestive of type I interferon activation in COVID-19 children, probably related to a recent interaction with the virus, while in MIS-C the immune response is characterized by elevation of the inflammatory cytokines/chemokines IL-6, CCL2, and CXCL8 and of the chemokines CXCL9 and CXL10, which are markers of an active Th1 type immune response. We believe that these immunological events, together with neutrophil activation, might be crucial in inducing the multisystem and cardiovascular damage observed in MIS-C.

Autoimmune and Rheumatic Manifestations Associated With COVID-19 in Adults: An Updated Systematic Review

Background: Numerous cases of the coronavirus disease 2019 (COVID-19) with autoimmune and rheumatic manifestations have been reported. Despite the available reviews that summarized its autoimmune/rheumatic manifestations, a systematic approach is still lacking. Therefore, we conducted a comprehensive systematic review in order to give an overview upon these rare but clinically significant manifestations.

Methods: We performed a literature search of PubMed and EMBASE as of October 9, 2020. All articles relevant to either systemic or organ-specific autoimmune and rheumatic manifestations potentially associated with COVID-19 were collected. The reviewed literature were limited to adults ≥18 years.

Results: Although most of the existing evidence was based on case reports or case series without a long-term follow-up, a variety of autoimmune/rheumatic manifestations were associated with COVID-19. The manifestations that have a consistent association with COVID-19 include autoimmune cytopenia, cutaneous vasculitis, encephalitis, and Guillain-Barre syndrome. Such association is conflicting as regards to antiphospholipid syndrome, hemophagocytic lymphohistiocytosis, and myasthenia gravis.

Conclusion: Our systematic review indicated the potential of the COVID-19 virus to trigger a myriad of autoimmune and rheumatic manifestations, which should be considered amid global efforts to combat COVID-19.

Haemophagocytic syndrome and COVID-19

Primary and secondary haemophagocytic lymphohistiocytosis (HLH) are hyperferritinaemic hyperinflammatory syndromes with a common terminal pathway triggered by different etiopathogenetic factors. HLH is characterised by a decreased capacity of interferon gamma production with an activated NK phenotype profile similar to other hyperinflammatory syndromes. Viruses are closely linked to the development of HLH as infectious triggers, and the break of tolerance to self-antigens is considered a critical mechanism involved in the development of immune-mediated conditions triggered by viral infections. Emerging studies in patients with COVID-19 are suggesting a key role of monocytes/macrophages in the pathogenesis of this viral infection, and there is a significant overlap between several features reported in severe COVID-19 and the features included in the HLH-2004 diagnostic criteria. Therefore, SARS-Cov-2, as other respiratory viruses, may also be considered a potential etiological trigger of HLH. The frequency of HLH in adult patients with severe COVID-19 is lower than 5%, although this figure could be underestimated considering that most reported cases lacked information about some specific criteria (mainly the histopathological criteria and the measurement of NK cell function and sCD25 levels). Because HLH is a multi-organ syndrome, the diagnostic approach in a patient with severe COVID-19 in whom HLH is suspected must be carried out in a syndromic and holistic way, and not in the light of isolated clinical or laboratory features. In COVID-19 patients presenting with persistent high fever, progressive pancytopenia, and hepatosplenic involvement, together with the characteristic triad of laboratory abnormalities (hyperferritinaemia, hypertriglyceridaemia, and hypofibrinogenaemia), the suspicion of HLH is high, and the diagnostic workup must be completed with specific immunological and histopathological studies.