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Hemophagocytic Lymphohistiocytosis

A 6-year-old girl presents to the emergency department with a two-week history of sore throat, fever, rash, generalized lymph node enlargement, worsening abdominal distension, and abdominal pain. On arrival her temperature is 39°C and she has palpable cervical adenopathy and splenomegaly. Laboratory data includes the following:

TestResultReference Range
WBC16.0 x 109/L4.27 - 11.40 x 109/L
HGB8.4 g/dL10.6 - 13.4 g/dL
HCT25.5%32.2% - 39.8%
MCV88 fL74.4 - 87.6 fL
PLT22 x 109/L150 - 400 x 109/L

Ferritin is elevated at 5500 µg/L (normal 14.7 to 205.1 µg/L), while triglycerides and fibrinogen are normal. She is admitted to the hospital service and a bone marrow biopsy is scheduled.

The child’s parents state there is no family history of any hematologic disorders. The bone marrow biopsy is performed and there are abnormal cells on the aspirate smears. Meanwhile additional laboratory testing shows the patient is positive for Epstein-Barr virus (EBV) IgM and IgG viral capsid antigen antibodies. Soluble CD25 (soluble IL-2 receptor) is elevated at 2,700 U/mL (normal 223 to 710 U/mL).

Bone marrow aspirate, Wright stain, 1000x

Master List of Diagnoses

  • Acute lymphoblastic leukemia
  • Acute myeloid leukemia
  • Aplastic anemia
  • Bartonella henselae lymphadenitis
  • Burkitt lymphoma
  • Hemophagocytic lymphohistiocytosis associated with infectious mononucleosis
  • Kikuchi-Fujimoto disease
  • Refractory cytopenia of childhood

This material was originally released as 2019 CPIP-J Case 10: Hematology – Timely Diagnosis of Hemophagocytic Lymphohistiocytosis.

Criteria for Diagnosis and Comments

The patient meets six of the eight HLH-2004 criteria for a diagnosis of hemophagocytic lymphohistiocytosis: fever, splenomegaly, bicytopenias (hemoglobin <9.0 g/dL and platelets <100 x 109), hemophagocytosis, hyperferritinemia, and elevated soluble CD25.

Hemophagocytic lymphohistiocytosis (HLH), also known as hemophagocytic syndrome, is a rare disease caused by dysregulated immune activation and is almost universally fatal if untreated. Even with current treatment regimens mortality is up to 40%.1 Patients usually present severely ill, most often with fever, splenomegaly, and cytopenias. The disease may also manifest with coagulopathy, hypertriglyceridemia, hepatic dysfunction, hyperferritinemia, and neurologic symptoms.2

HLH is a manifestation of an inappropriate immune response including dysfunction in NK/T-cell activity and hypercytokinemia resulting in activation of macrophages and cytotoxic T-cells, downregulation of regulatory T-cells, and ultimately organ damage. The cytokine storm includes elevated levels of IFNγ, IL1β, IL6, IL12, IL18, and TNF. These cytokines illicit some of the classic features of HLH such as fever and cytopenias, and higher cytokine levels may be associated with worse outcomes.1

In HLH hemophagocytic macrophages may be present in the bone marrow, spleen, liver, enlarged lymph nodes, or cerebrospinal fluid, however this finding is neither entirely specific nor sensitive for HLH. Hemophagocytic cells can be seen in the context of other conditions such as sepsis, myelodysplastic syndromes, and after transfusion, hematopoietic stem cell transplant, or chemotherapy.3

There are two forms of HLH, primary and secondary. Primary or familial HLH is an autosomal recessively inherited disorder. The disease is rare with an estimated incidence of 1:50,000 to 1:100,000 children. Patients usually present in early infancy or adulthood, and the syndrome may be triggered after infection.4 Mutations are in genes that regulate granulocyte-dependent lymphocyte activity, exemplified by the first gene implicated, PRF1 (encoding perforin). Other implicated genes include UNC13D (Munc 13-4), STX11 (syntaxin 11), and STXBP2 (syntaxin-binding protein 2). There are other inherited conditions affecting granule trafficking including Griscelli syndrome type II (RAB27A gene), Chediak-Higashi syndrome (LYST), and Hermansky-Pudlak syndrome type II (AP3B1) that can also develop HLH. Furthermore, genes affecting regulation of EBV reactivation such as those involved in X-linked lymphoproliferative disease XLP1 and XLP2 (SH2D1A and BIRC4/XIAP) have been implicated. It is likely other genes will continue to be added.5

Secondary HLH (sHLH) is caused by an inappropriate response to immune stimulation, such as severe infection, autoimmune disease, or malignancy. Secondary HLH is seen in all age groups, without preference for gender. Heterozygous mutations in some genes associated with primary HLH have been found in patients with sHLH, suggesting there may be a component of genetic predisposition in some patients.5

Macrophage activation syndrome refers to HLH arising in a background of autoimmune disease. Recent consensus guidelines recommend that this term be restricted to cases of HLH in patients with Still’s disease, systemic lupus erythematosus, vasculitis, and other systemic autoimmune diseases, because treatment of this condition may differ from that of other forms of HLH.6

Many other conditions can trigger HLH. Secondary HLH has also been reported at the most severe form of cytokine release syndrome associated with chimeric antigen receptor (CAR) T-cell therapy, and may be increasingly seen as this therapy is more broadly applied.7 There have also been striking associations of HLH presenting shortly after administration of lamotrigine, an anti-seizure medication also used to treat bipolar disorder.8

The most widely used diagnostic criteria for HLH are based on the Histiocyte Society’s 2004 revision of the HLH-94 guidelines used for clinical trials in pediatric patients. Although these have not been specifically validated in adults, they are currently widely used in the adult population as well.6

HLH-2004 criteria for diagnosis of HLH requires either 1 or 2:

  1. A molecular diagnosis consistent with HLH
  2. Diagnostic criteria for HLH fulfilled (five out of the eight criteria below)
    • Fever
    • Splenomegaly
    • Cytopenias affecting two or three lineages
    • Hemoglobin <9.0 g/dL (<10.0 g/dL in infants younger than four weeks)
    • Platelets <100 x 109/L
    • Neutrophils <1.0 x 109/L
    • Hypertriglyceridemia and/or hypofibrinogenemia
    • Fasting triglycerides ≥3.0 mmol/L (≥265 mg/dL)
    • Fibrinogen ≤1.5 g/L
    • Hemophagocytosis in bone marrow, spleen, or lymph nodes
    • Low or absent NK cell activity (according to laboratory reference ranges)
    • Ferritin ≥500 µg/L
    • Soluble CD25 (soluble IL-2 receptor) ≥2,400 U/ml

Modified from Henter JI et al. Pediatr Blood Cancer. 2007.

In all cases of hemophagocytic lymphohistiocytosis, every effort should be made to identify the underlying condition. In children, distinguishing primary HLH from secondary forms is especially important; although initial treatment is generally the same, patients with primary forms are treated with ongoing therapy and eventual hematopoietic stem cell transplant (HSCT). This patient’s symptoms including fever, pharyngitis, lymphadenopathy, and splenomegaly are consistent with infectious mononucleosis, as confirmed by the serologic testing. Infection is the most common trigger for secondary HLH, especially in children. The most implicated agents are viruses, especially EBV, although a wide variety of bacteria, fungi, and parasites have been reported to trigger HLH.5 Even if an infectious agent is found for HLH in a pediatric patient, it is still recommended to perform molecular testing to evaluate for primary HLH, since the onset of an HLH episode may be triggered by infection in these patients. However treatment should not be delayed while waiting for molecular testing if the patient meets diagnostic criteria.6

The mainstay of therapy for all cases of HLH has been etoposide combined with dexamethasone (in conjunction with treating the underlying disorder in secondary cases). FHLH specifically is rapidly fatal if untreated, with a mean survival of two months.2

In refractory cases, a variety of therapies have been attempted including anakinra, anti-thymocyte globulin, alemtuzumab, and doxorubicin, with varying success.4 Recently a new drug, emapalumab-Izsg, a monoclonal antibody against interferon gamma, has been approved in the United States for primary HLH that is refractory to conventional therapy.9

Essentially all familial cases and some cases of secondary refractory HLH are recommended to undergo HSCT. Sibling HLA-matched donors are recommended to decrease risk of graft-versus-host disease. Potential donors should be screened for HLH-associated mutations. Some authors are comfortable using a sibling as a donor even if they have one of the affected mutations.4 However siblings with bi-allelic mutations should not be used as donors and there is even some evidence that transplanting these affected siblings while asymptomatic may lead to better overall survival than waiting for HLH to manifest.10

HLH in adults appears to present somewhat differently than in children. Increasing evidence has shown that certain diagnostic parameters may not be as meaningful in adults. Hyperferritinemia of 10,000 µg/L is reportedly over 90% sensitive and specific in the pediatric population but less specific in adults. It has been suggested that the soluble CD25 assay is a better distinguishing test in this population with an area under the curve of 0.90 compared to 0.78 for ferritin.6 Other findings that may be helpful for diagnosing HLH in adults include markers of liver abnormalities including hepatomegaly, hyperbilirubinemia, and transaminitis as well as elevated lactate dehydrogenase and D-dimer. While additional work remains to be done to validate these classifiers, a working group on adult HLH sponsored by the Histiocyte Society has recently recommended the HScore, an online HLH-probability calculator to aid in diagnosis in adults.6,11 Retrospective pathology review of cases where bone marrow biopsies were obtained for suspicion of HLH have shown that NK cell activity was the least frequently tested parameter in both studies, performed only once in one study, and showed the lowest sensitivity for diagnosis in the other.3,12

While infection, especially EBV, remains a common underlying cause for sHLH in adults, there is an increased frequency of malignancy-associated cases compared to pediatric cases. In some Western series, malignancy-associated cases were actually more common than infection-associated cases.13,14 However there is likely a geographic variation to the frequencies of each.15 In adults the malignancies associated with sLHL are usually of malignant lymphocytes, slightly more often T/NK-cell lineage than B-cell (together 60% to 70% of cases).6 The major implication for this finding is that the underlying disease must be appropriately treated in order to treat the HLH. Prognosis is abysmal, usually less than two months survival and death often within two weeks.17

  1. Hemophagocytic lymphohistiocytosis can be both an inherited and acquired disorder

    1. True
    2. False
  2. Which of the following is one of the HLH-2004 diagnostic criteria for HLH?

    1. Underlying hematologic malignancy
    2. Soluble CD25 ≥2,400 U/ml
    3. Neutrophilia (absolute neutrophil count >10 x 109/L)
    4. Palpable lymphadenopathy


  1. Bergsten E, Horne AC, Aricó M, et al. Confirmed efficacy of etoposide and dexamethasone in HLH treatment : long-term results of the cooperative HLH-2004 study. Blood. 2017 Dec 21;130(25):2728-39. doi:10.1182/blood-2017-06-788349.
  2. Henter JI, Horne A, Aricó M, et al. HLH-2004: Diagnostic and therapeutic guidelines for hemophagocytic lymphohistiocytosis. Pediatr Blood Cancer. 2007;48(2):124-31. doi:10.1002/pbc.21039.
  3. Gars E, Purington N, Scott G, et al. Bone marrow histomorphological criteria can lymphohistiocytosis. Haematologica. 2018 Oct;103(10):1635-41. doi:10.3324/haematol.2017.186627.
  4. Marsh RA, Haddad E. How i treat primary haemophagocytic lymphohistiocytosis. Br J Haematol. 2018;182(2):185-99. doi:10.1111/bjh.15274.
  5. Allen CE, Mcclain KL. Pathophysiology and epidemiology of hemophagocytic lymphohistiocytosis. ASH Educ Progr B. 2015;2015:177-82. doi:10.1182/asheducation-2015.1.177.
  6. La Rosée P, Horne A, Hines M, et al. Recommendations for the management of hemophagocytic lymphohistiocytosis in adults. Blood. 2019:blood.2018894618. doi:10.1182/blood.2018894618.
  7. Brudno JN, Kochenderfer JN. Recent advances in CAR T-cell toxicity: Mechanisms, manifestations and management. Blood Rev. 2019;34:45-55. doi:10.1016/j.blre.2018.11.002.
  8. Kim T, Kulick CG, Kortepeter CM, Brinker A, Waldron P. Hemophagocytic lymphohistiocytosis associated with the use of lamotrigine. Neurology. 2019:10.1212/WNL.0000000000007517. doi:10.1212/wnl.0000000000007517.
  9. Al-Salama ZT. Emapalumab : First global approval. Drugs. 2019Jan ;79(1):99-103. doi:10.1007/s40265-018-1046-8.
  10. Lucchini G, Marsh R, Gilmour K, et al. Treatment dilemmas in asymptomatic children with primary hemophagocytic lymphohistiocytosis. Blood. 2018;132(19):2088-96. doi:10.1182/blood-2018-01-827485.
  11. Fardet L, Galicier L, Lambotte O, et al. Development and validation of the hscore, a score for the diagnosis of reactive hemophagocytic syndrome. Arthritis Rheumatol. 2014;66(9):2613-20. doi:10.1002/art.38690.
  12. Ho C, Yao X, Tian L, Li FY, Podoltsev N, Xu ML. Marrow assessment for hemophagocytic lymphohistiocytosis demonstrates poor correlation with disease probability. Am J Clin Pathol. 2014;141(1):62-71. doi:10.1309/AJCPMD5TJEFOOVBW.
  13. Parikh SA, Kapoor P, Letendre L, Kumar S, Wolanskyj AP. Prognostic factors and outcomes of adults with hemophagocytic lymphohistiocytosis. Mayo Clin Proc. 2014;89(4):484-92. doi:10.1016/j.mayocp.2013.12.012.
  14. Schram AM, Comstock P, Campo M, et al. Haemophagocytic lymphohistiocytosis in adults: A multicentre case series over 7 years. Br J Haematol. 2016;172(3):412-9. doi:10.1111/bjh.13837.
  15. Ramos-Casals M, Brito-Zerón P, López-Guillermo A, Khamashta MA, Bosch X. Adult haemophagocytic syndrome. Lancet. 2014;383(9927):1503-16. doi:10.1016/S0140-6736(13)61048-X.
  16. Pasvolsky O, Lorenz AZ, Abadi U, et al. Hemophagocytic lymphohistiocytosis as a harbinger of aggressive lymphoma : a case series. Int J Hematol. 2019;109(5):553-62. doi:10.1007/s12185-019-02623-z.
  17. Daver N, McClain K, Allen CE, et al. A consensus review on malignancy-associated hemophagocytic lymphohistiocytosis in adults. Cancer. 2017;123(17):3229-40. doi:10.1002/cncr.30826.


Megan O. Nakashima, MD, FCAP
Assistant Professor, Cleveland Clinic Lerner College of Medicine

Answer Key

  1. True (a)
  2. Soluble CD25 ≥2,400 U/ml (b)