Lymphohistiocytosis (Hemophagocytic Lymphohistiocytosis)

Cutaneous involvement occurs in as many as 65% of patients with hemophagocytic lymphohistiocytosis (HLH).[3] Varied skin manifestations of HLH are noted, including erythroderma, generalized purpuric macules and papules, and morbilliform eruptions. Detection of cutaneous involvement can assist in the initial diagnosis of HLH and can potentially signify recurrences. Hemophagocytic lymphohistiocytosis may be viewed as a marker for underlying cancer, which in adults is most often a lymphoma that may be rapidly progressive.[4]

Primary hemophagocytic lymphohistiocytosis (ie, familial erythrophagocytic lymphohistiocytosis [FEL]), an inherited form of hemophagocytic lymphohistiocytosis syndrome, is a heterogeneous autosomal recessive disorder found to be more prevalent with parental consanguinity. Secondary hemophagocytic lymphohistiocytosis (ie, acquired hemophagocytic lymphohistiocytosis) occurs after strong immunologic activation, such as that which can occur with systemic infection, immunodeficiency, or underlying malignancy. Both forms are characterized by the overwhelming activation of normal T lymphocytes and macrophages, invariably leading to clinical and hematologic alterations and death in the absence of treatment.[5]

Drug reaction with eosinophilia and systemic symptoms (DRESS) is also a hypersensitivity reaction with overlapping syndromes with HLH, specifically dermatitis, lymphadenopathy, fever, eosinophilia, and visceral organ involvement.[6, 7] DRESS is associated with reactivation of herpes viruses with activated CD8+ T lymphocytes directed against them. Thus, patients with DRESS should be evaluated for the development of HLH, including for reactivation of human herpes viruses such HHV-6, HHV-7 and Epstein-Barr virus (EBV), and coagulation function evaluations.[8]

The history of this disorder, its molecular basis, and treatment options are noteworthy.[9] Almost 60 years has passed since Scottish pediatricians James Farquhar and Albert Claireaux, both of the University of Edinburgh, noticed the familial recurrence of this disorder affecting male and female siblings aged 2 months, causing fever, cytopenia, hepatosplenomegaly, and rapidly death despite treatment with antibiotics and steroids.[10]

The pathologic hallmark of this disease is the aggressive proliferation of activated macrophages and histiocytes, which phagocytose other cells, namely red blood cells (RBCs), white blood cells (WBCs), and platelets, leading to the clinical symptoms. The uncontrolled growth is nonmalignant and does not appear clonal in contrast to the lineage of cells in Langerhans cells histiocytosis (histiocytosis X). The spleen, lymph nodes, bone marrow, liver, skin, and membranes that surround the brain and spinal cord are preferential sites of involvement.[11] This disorder may be viewed as a highly stimulated, but ineffective, immune response to antigens, which results in life-threatening cytokine storm and inflammatory reaction.[12]

Over the past 2 decades, the underlying pathophysiology of hemophagocytic lymphohistiocytosis has been characterized, although the processes are not entirely understood. A current accepted theory involves an inappropriate immune reaction caused by proliferating and activated T cells associated with macrophage activation and inadequate apoptosis of immunogenic cells.[13] Although the precise mechanism remains unclear, many research teams propose convincing pictures for the role of perforin and natural killer (NK) cells in the hemophagocytic lymphohistiocytosis subtypes.[14, 15, 16]

Perforin or pore-forming protein (PFP), gene map location 10q22, is one of the major cytolytic proteins of granules contained in cytotoxic cells.[17] When activated by a challenge, NK cells release granules that contain perforin and granzymes, which form pores in the target cell membrane and cause osmotic lysis and protein degradation, respectively. Additionally, the endocytotic and exocytotic mechanisms may also be affected.[18] Patients with perforin deficiency may have impaired defenses against intracellular pathogens and cancers, as has been demonstrated in animal models.

Although the mechanism is yet to be determined, decreased NK cell activity results in increased T-cell activation and expansion, with resulting production of large quantities of cytokines, including interferon gamma (IFNg), tumor necrosis factor-α (TNF-α), and granulocyte-macrophage colony-stimulating factor (GM-CSF). This causes sustained macrophage activation and tissue infiltration as well as production of interleukin-1 (IL-1) and interleukin-6 (IL-6). The resulting inflammatory reaction causes extensive damage and the associated symptoms.[19]

While mutations in STX11 are said to be responsible for much of the familial hemophagocytic lymphohistiocytosis in the Middle East, one survey found such mutations in only 1% of North American patients.[20]

The familial form is a rare autosomal recessive disorder that has been classified into 6 different types based on genetic linkage analysis and chromosomal localization; 5 specific genetic defects have been identified, which account for approximately 90% of all patients.[21]  Type 1 is due to a gene defect on chromosome 9, type 2 is due to mutations in the perforin gene, type 3 is due to mutations in the Munc-13-4 (UNC13D) gene, type 4 is due to mutations in the syntaxin 11 (STX11) gene, and type 5 is due to mutations in the gene encoding syntaxin binding protein 2 (STXBP-2).

Epstein-Barr virus (EBV) is the pathogen that most commonly triggers infection-associated hemophagocytic lymphohistiocytosis. One study showed a vulnerability to EBV infection in Korean children.[22] Epstein-Barr virus also infects CD8(+) T cells in EBV-associated hemophagocytic lymphohistiocytosis.[23, 24] Demonstrating these cells by their immunophenotypic characteristics may aid in the diagnosis of EBV-associated hemophagocytic lymphohistiocytosis. However, in a Brazilian sampling of 50 patients, 34 adults and 16 children, EBV infection was found to be less common in adults than in children.[25]

Hemophagocytic lymphohistiocytosis may be a complication of dengue, although this association is unusual.[26, 27]  Scrub typhus may also be linked.[28]

The tick-borne parasitic infection babesiosis can have findings ranging from mild anemia to hemophagocytic lymphohistiocytosis.[29]  One should also consider ehrlichiosis as a possible trigger of hemophagocytic lymphohistiocytosis.[30]

Hemophagocytic lymphohistiocytosis may be a complication of the DRESS syndrome.[8]

International statistics

Incidence is reported to be 1.2 cases per million persons per year. However, unpublished observations estimate that the figures have slightly increased over time because of improved detection.[31] This amounts to 1 case per every 50,000 births.[32]

Perforin mutations account for approximately 20% of cases of FEL, with a somewhat higher prevalence (30%) in children of Turkish descent. Chromosome arm 9q mutations account for approximately 10% of familial cases; the remainder of FEL cases are caused by mutations in as yet unidentified genes.[33]

Race-, sex-, and age-related demographics

Hemophagocytic lymphohistiocytosis has not been epidemiologically shown to have a predilection for persons of any race. A sample of European countries, including Sweden, England, and Italy, has reported similar statistical incidences.[19]

The disease has an equal distribution among males and females.

The age of onset is usually in persons younger than 1 year for the familial form but can be later for the secondary sporadic form, usually after age 6 years.[13] Although the familial form of the disease frequently affects infants from birth to age 18 months, familial forms have been reported in individuals as old as 8 years, and adult onset has been reported. At this point, no criteria for age have been established, and an upper age limit does not exist.[32]

Morbidity/mortality

Familial hemophagocytic lymphohistiocytosis is uniformly fatal if not treated; the median survival time reported in various studies is 2-6 months after diagnosis. The historical series collected by the International Hemophagocytic Lymphohistiocytosis Registry reports a less than 10% probability that the patient survives for 3 years.[34]  Even with treatment, only 21-26% can be expected to survive 5 years. Remission is always temporary, as the disease inevitably returns. Bone marrow transplant is the only hope for cure. One study found that 50% of deaths from FEL were due to invasive fungal infections, which are probably underdiagnosed.[32]  The outcomes of secondary hemophagocytic lymphohistiocytosis vary.

A study of 122 patients from the International Registry for hemophagocytic lymphohistiocytosis found that the overall estimated 5-year survival rate was 21%, with 66% of patients who received bone marrow transplantation (BMT) surviving 5 years versus only 10.1% of patients treated with chemotherapy alone.[34]  More recent studies have shown that the HLH-94 protocol resulted in an overall survival rate of 55%. Success or failure of an allogeneic BMT is the most important long-term prognostic factor. Unfortunately, many cases are diagnosed late in the course of the disease, after irreversible damage has occurred.

Although patients with hemophagocytic lymphohistiocytosis are at high risk for death early in their disease course, steroids, intravenous immunoglobulin (IVIG), or both may be sufficient as first-line therapy for selected patients.[35]

The ratio of C16-ceramide to sphingosine was elevated in those who died despite appropriate treatment, but remained low in survivors, implying that this ratio may be of prognostic significance.[36]  The balance of ceramide and sphingosine may be pivotal in the clinical outcome for these patients.

Complications

Complications of individual drugs in the treatment regimen are outlined in the Medication section.

Complications due to a subsequent transplant are numerous and include both acute and chronic graft versus host disease, acute inflammatory events, respiratory distress syndrome, and exacerbation of neurologic symptoms.[37]

All physicians who treat young patients must be aware of life-threatening diseases such as hemophagocytic lymphohistiocytosis. Pediatricians, dermatologists, and neurologists should especially take note because the presenting symptoms of hemophagocytic lymphohistiocytosis are likely to bring the patient into their offices. Any suspicion warrants a referral to a pediatric hematologic-oncologist who is equipped with the necessary tools to make a rapid diagnosis.

The diagnostic criteria set forth by the Histiocyte Society for inclusion in the International Registry for Hemophagocytic Lymphohistiocytosis (HLH) is as follows.[1] All 5 criteria must be met to establish a diagnosis of hemophagocytic lymphohistiocytosis:

• Fever - Seven or more days of a temperature as high as 38.5°C (101.3°F)

• Splenomegaly - A palpable spleen greater than 3 cm below the costal margin

• Cytopenia - Counts below the specified range in at least 2 of the following cell lineages:

  • Absolute neutrophil count of less than 1000/µL (see Differential Blood Count)

  • Platelet count of less than 100,000/µL

  • Hemoglobin level of less than 9.0 g/dL

• Hypofibrinogenemia or hypertriglyceridemia - (1) Fibrinogen less than 1.5 g/L or levels greater than 3 standard deviations below the age-adjusted reference range value or (2) fasting triglycerides greater than 2 mmol/L or levels greater than 3 standard deviations above the age-adjusted reference range value

• Hemophagocytosis - Must have tissue demonstration from lymph node, spleen, or bone marrow without evidence of malignancy

Skin findings are noted in more than half of patients, such as scaly and waxy lesions and rashes on the scalp and behind the ear.[3]  Other findings include swollen or hemorrhagic gums that can result in tooth loss; feeding problems (especially prominent in infants); and abdominal pain, vomiting, diarrhea, and weight loss.

Hemophagocytic lymphohistiocytosis was noted in a boy with Chédiak-Higashi syndrome.[38]  In a sampling from Brazil, 90% of patients with hemophagocytic lymphohistiocytosis had fever and thrombocytopenia, although in adults, hepatomegaly, splenomegaly, and jaundice were less common than in children, and serous cavity effusion was more frequent.[25]

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be a trigger for hemophagocytic lymphohistiocytosis.[39]  Prompt recognition in patients with coronavirus disease 2019 (COVID-19) may improve clinical outcomes. Mortality in patients with hemophagocytic lymphohistiocytosis who have COVID-19 is high.

Clinical findings, including evidence of infection due to decreased immunity and white cell killing defects, easy bruisability, and pallor, are related to pancytopenia secondary to bone marrow infiltration or splenic sequestration.

Evidence of a coagulopathy with an increased activated partial thromboplastin time (aPTT) is present.

Jaundice is often present due to hyperbilirubinemia.

The skin can be involved in various ways. As many as 65% of patients have a nonspecific rash that is often vaguely termed maculopapular, although it has also been described as ranging from erythroderma to generalized purpuric macules and papules to morbilliform eruptions.[3]

Hemophagocytic lymphohistiocytosis may be complicated by central nervous system (CNS) involvement. [40]  One Swedish study described nearly 75% of patients as having some form of CNS involvement, with half showing neurologic symptoms including seizures, ataxia, hemiplegia, mental status changes, or simply irritability.[41]

Because of the predilection of the disease for certain tissues, lymphadenopathy is frequently found on physical examination. Common constitutional findings are malaise, anorexia with or without weight loss, and failure to thrive.[1]

Because natural killer (NK) cell function or activity is decreased in as many as 90% of patients with hemophagocytic lymphohistiocytosis (HLH), it is one of the most useful laboratory tests. NK cell number is usually not diagnostic.

In addition to pancytopenia, hypofibrinogenemia, and hypertriglyceridemias, other laboratory abnormalities have been linked to HLH. Ferritin has been observed as a marker for hemophagocytic lymphohistiocytosis, with the serum levels paralleling the course of the disease.[42] A retrospective study evaluated the use of a ferritin value of >500 ng/mL in diagnosing HLH in 344 consecutive patients admitted to the medical intensive care unit. The data suggested that a higher cutoff value of ferritin may have improved utility in the diagnosis of secondary hemophagocytic lymphohistiocytosis in the critical care setting.[43]

Liver damage has also been reported as evidenced by hyperbilirubinemia (see Bilirubin), hypoalbuminemia (see Albumin), and elevated findings on liver function tests including aspartate aminotransferase (AST) and alanine aminotransferase (ALT).[44]

The presence of a PRF1 gene mutation can be determined based on flow cytometry by staining perforin contained in lymphocytes.

The finding of a distinctive Th1/Th2 cytokine pattern (significant increase of interferon [IFN]-ƒ× and interleukin-10 [IL-10] with slightly increased or normal level of IL-6) may represent a useful biomarker for the early diagnosis, differential diagnosis, and the monitoring of the disease.[12]

No specific imaging patterns are diagnostic of hemophagocytic lymphohistiocytosis.

Computed tomography (CT) or ultrasonography findings may include ascites, gallbladder wall thickening, increased periportal echogenicity, lymphadenopathy, and pleural effusion.

Magnetic resonance imaging (MRI) may show central nervous system (CNS) involvement, but the diagnosis is clinical and molecular.[45]

Arico et al proposed an approach to the diagnostic workup of a patient with suspected hemophagocytic lymphohistiocytosis.[11]  A detailed clinical history should be obtained to exclude other associated conditions, such as metabolic disorders or the DiGeorge syndrome. However, if the diagnostic hemophagocytic lymphohistiocytosis criteria are fulfilled, and the findings for associated conditions are negative, initial testing involves perforin expression by NK cells using flow cytometry.

Patients who lack perforin expression should be analyzed for the PRF1 gene mutation. NK cell activity should also be determined to aid in differentiating between the hemophagocytic lymphohistiocytosis subtypes. Normal activity is suggestive of the reactive form of hemophagocytic lymphohistiocytosis rather than the familial type.

DNA samples and fresh cells are suggested to be stored in case of need for future use in familial cases for which no genetic defect can be identified.

A skin biopsy can be performed for histologic examination. Lymph node biopsy (see the image below), bone marrow biopsy, or liver biopsy may demonstrate the characteristic hemophagocytosis.

A lymph node biopsy is performed. Note that a marking pen has been used to outline the node before removal and that a silk suture has been used to provide traction to assist the removal.

A skin biopsy can assist in distinguishing this disorder from other systemic and potentially neoplastic diseases, such as Langerhans cell histiocytosis, myofibrosis, extramedullary hematopoiesis, and leukemia cutis.[3, 46] However, skin biopsy findings are usually not diagnostic and only rarely show hemophagocytosis.

Because hemophagocytosis must be demonstrated in the bone marrow, spleen, or lymph nodes, appropriate specimens should be collected for documentation.[1] Red blood cells are affected more often than white blood cells or platelets.

Findings in up to two thirds of initial bone marrow aspirates may be nondiagnostic; thus, a negative examination finding may not rule out hemophagocytic lymphohistiocytosis. An additional bone marrow finding includes dyserythropoiesis, which has been observed in the absence of hemophagocytic histiocytes.

Additional studies, including lymph node biopsy, should be performed, and treatment should not be delayed if all other criteria have been met.[47]

Although problematic in a patient with a coagulopathy, a liver biopsy demonstrating a picture similar to chronic persistent hepatitis can support the diagnosis, as can the presence of mononuclear cells in the cerebrospinal fluid (CSF).

Rapid diagnosis and early therapy can be pivotal.[48]  A pediatric hematology-oncology specialist is best equipped to manage hemophagocytic lymphohistiocytosis (HLH), which is a rare and potentially life-threatening disease.

Emapalumab, a monoclonal antibody that binds and neutralizes INF-gamma, was approved by the FDA in 2018. It is indicated for primary HLH in adults and children with refractory, recurrent, or progressive disease or who are intolerant to conventional HLH therapy. Approval was based on a phase 2/3 trial of 27 patients with refractory, recurrent, or progressive HLH. Result showed 63% achieved either a complete response, a partial response, or HLH improvement of emapalumab plus dexamethasone. Additionally, 70% of trial participants were able to continue on to hematopoietic stem cell transplant (HSCT).[49]  Emapalumab was found beneficial for primary hemophagocytic lymphohistiocytosis.[2]

Protocol HLH-2004, opened on January 1, 2004, is based on the Histiocyte Society's original HLH-94 protocol, which had previously opened on January 1, 1995, with some minor modifications. The full HLH-2004 protocol is available by contacting the Histiocytosis Association of America. It represents a consolidation of the various approaches to treatment, with the goals being to first achieve clinical stability and then to cure with bone marrow transplantation (BMT).

Antimycotic prophylaxis is used during the initial doses of dexamethasone. Sulfamethoxazole and trimethoprim (ie, cotrimoxazole) is continuously administered as prophylaxis for Pneumocystis carinii because of immune suppression.[50]

One group found that intravenous immunoglobulin (IVIG) was effective in suppressing symptoms when administered within hours of disease onset. Serum ferritin was used as a marker for macrophage activation, and treatment was administered accordingly.[51] Patients may be classified into high-risk and low-risk groups, with only the high-risk groups receiving the etoposide (ie, VP-16) regimens. Patients who are at low risk may be treated as effectively with only cyclosporine, corticosteroids, or IVIG.[42] More studies, including randomized controlled trials, are needed.

Persons with hemophagocytic lymphohistiocytosis may be at increased risk for developing posterior reversible encephalopathy syndrome.[52]  Central nervous system (CNS) involvement of hemophagocytic lymphohistiocytosis may trigger this syndrome and other neurotoxic side effects experienced during therapy.

Bone marrow transplantation is performed when a suitable donor can be found and the patient is stable.

A study has found favorable long-term disease control in patients who received a reduced-intensity conditioned regimen instead of the conventional stem cell transplant.[53]

If the patient is experiencing life-threatening respiratory difficulty or uncontrolled hypersplenism, splenectomy is an option.

Consultation with a gastroenterologist may be helpful, especially if a transcutaneous liver biopsy is necessary.

If the primary form of hemophagocytic lymphohistiocytosis is suspected, a genetic counselor may be helpful. In addition to analyzing inheritance patterns and determining risk, they can provide supportive counseling to the patient and family.

This life-threatening hyperinflammatory syndrome is difficult to treat.[54] Initial therapy in patients with hemophagocytic lymphohistiocytosis (HLH) consists of etoposide and dexamethasone for 8 weeks in varying doses as described below.[55] In the HLH-2004 protocol, cyclosporine is added in the beginning. Intrathecal methotrexate is used only with persistently abnormal cerebrospinal fluid (CSF) or progressive neurologic symptoms.

Resolved nonfamilial hemophagocytic lymphohistiocytosis does not require continuation of the therapy regimen unless disease reactivation occurs after completion of the initial therapy or unless patients are undergoing bone marrow transplantation (BMT). For the remaining children with persistent nonfamilial disease or familial disease, continuation therapy with etoposide intravenous (IV) infusions, dexamethasone pulses, and oral cyclosporine is instituted at week 9 from the start of initial treatment.[50]

Emapalumab, a monoclonal antibody that binds and neutralizes INF-gamma, was approved by the FDA in 2018. It is indicated for primary HLH in adults and children with refractory, recurrent, or progressive disease or who are intolerant to conventional HLH therapy.[49]

Alemtuzumab may be an effective salvage agent for refractory HLH, with retrospective trials needed to define optimal dosing.[54]

Hemophagocytic lymphohistiocytosis associated with malignancies demands prompt therapy directed at the neoplasm.

Class Summary

These agents interfere with cell reproduction. Some agents are cell cycle specific, whereas others (eg, alkylating agents, anthracyclines, cisplatin) are not phase specific. Cellular apoptosis (ie, programmed cell death) is also a potential mechanism of many antineoplastic agents.

Etoposide (Toposar, VePesid)

Also called VP-16. Inhibits topoisomerase II and results in DNA strand breakage causing cell proliferation to arrest in late S or early G2 portion of the cell cycle.

Methotrexate (Trexall)

Antimetabolite that inhibits dihydrofolate reductase, thereby hindering DNA synthesis and cell reproduction in malignant cells. Satisfactory response observed 3-6 wk following administration.

Adjust dose gradually to attain satisfactory response.

Class Summary

These agents elicit anti-inflammatory properties and cause profound and varied metabolic effects. They modify the body's immune response to diverse stimuli.

Dexamethasone (Decadron, Hexadrol)

Decreases inflammation by suppressing migration of polymorphonuclear leukocytes and reducing capillary permeability. Postulated mechanisms of action of corticosteroids in tumors include reduction in vascular permeability, cytoxic effects on tumors, and inhibition of tumor formation.

Class Summary

These agents may be used in combination with corticosteroids and immune globulin in patients at low risk.

Cyclosporine (Sandimmune, Neoral)

Cyclic polypeptide that suppresses some humoral immunity and, to a greater extent, cell-mediated immune reactions such as delayed hypersensitivity, allograft rejection, experimental allergic encephalomyelitis, and graft versus host disease for various organs.

In children and adults, base dosing on ideal body weight.

Class Summary

Elevated interferon-gamma (INF-gamma) is thought to be part of the pathogenesis that causes the hyperinflammation associated with HLH. Controlling the inflammation helps maintain organ function while preparing for hematopoietic stem-cell transplant (HSCT).

Emapalumab (Gamifant, emapalumab-lzsg)

Human monoclonal antibody that binds to and neutralizes interferon-gamma (IFN-gamma). It is indicated for primary HLH in adults and children (newborn and older) with refractory, recurrent, or progressive disease or who are intolerant to conventional HLH therapy.

Class Summary

Immune globulin is a purified preparation of gamma globulin. It is derived from large pools of human plasma and is comprised of 4 subclasses of antibodies, approximating the distribution of human serum.

Immune globulin, intravenous (Carimune NF, Gamumex, Gammagard)

Neutralizes circulating myelin antibodies through anti-idiotypic antibodies. Down-regulates proinflammatory cytokines, including INF-γ. Blocks Fc receptors on macrophages. Suppresses inducer T and B cells and augments suppressor T cells. Blocks complement cascade. Promotes remyelination. May increase CSF IgG (10%).

Supportive care is needed to ensure that the patient with hemophagocytic lymphohistiocytosis (HLH) remains stable until a bone marrow donor can be found. This includes transfusions of red blood cells, platelets, and fresh frozen plasma, as well as nutritional support in addition to the treatment protocol.[50]

Patients should be continually monitored for evidence of infection because of their immunosuppressed state. Be aware of the possibility of underlying malignancy.

Biopsies and diagnostic cytogenetics may be needed in addition to selective radiographic imaging.[32]