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Difference Between HLH and MAS

A brief overview of HLH and MAS

HLH (Hemophagocytic Lymphohistiocytosis) and MAS (Macrophage Activation Syndrome) both involve abnormal activation of the immune system.

however, each condition possesses distinct features:


  • HLH can be primary (genetic mutations) or secondary (due to infections, malignancies, autoimmune disorders, etc.).
  • It involves the abnormal function of natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), leading to excessive cytokine release.
  • Symptoms include fever, hepatosplenomegaly, cytopenias, coagulopathy, and organ dysfunction.
  • Diagnosis is based on specific criteria, including genetic testing and laboratory markers.
  • Treatment typically involves immunosuppression, chemotherapy, and hematopoietic stem cell transplant (in severe cases).


  • MAS is primarily associated with autoimmune disorders, particularly systemic juvenile idiopathic arthritis (sJIA).
  • It is characterized by an abnormal activation of macrophages and T cells, leading to cytokine storm.
  • Symptoms include high fever, rash, arthritis, hepatosplenomegaly, and potential organ damage.
  • Diagnosis is based on clinical and laboratory findings, including elevated ferritin levels and evidence of organ dysfunction.
  • Treatment involves controlling the underlying autoimmune disease and often requires immunosuppressive therapy, such as corticosteroids and biologic agents.

Though HLH and MAS may share similarities, their causes, immune reactions, and associated conditions vary considerably – thus prompt diagnosis is key for improved results in either condition.

What is HLH?

Hemophagocytic lymphohistiocytosis (also known as HLH is a disorder of the immune system. When this kind of condition occurs it is a sign that a part of your immune system absent or ineffective. The body doesn’t combat infections in the way it is supposed to. In the end, those suffering from HLH might experience frequently-recurring infections which tend to be much more intense and can last for longer than normal.

Hemophagocytic Lymphohistiocytosis (HLH)
Figure 01: Hemophagocytic Lymphohistiocytosis (HLH)

In HLH the white blood cells (T macrophages and lymphocytes) can’t be made to turn off. They accumulate in various organs, including the spleen, skin and the liver. They then kill the other blood cells like platelets, red blood cells and neutrophils. They also end up damaging organs affected by the disease.

There are two forms of the HLH. “Primary,” or “familial,” HLH can be due to an inheritable issue with an immune system. “Secondary” HLH can occur when the immune system has been disrupted (e.g. infections, etc.) however, it is not always due to an inheritance issue. Both kinds of HLH are potentially life-threatening. HLH could result in liver failure breathing issues as well as inflammation in the brain, as well as difficulty in fighting infection.

HLH is more common when children and infants are present. However, it is possible to experience it any time, and even teens and the adulthood stage.

HLH is considered to be a rare illness. The statistics indicate that it is present in approximately one child in every 50,000. Due to this, most healthcare professionals are not familiar of its signs and symptoms. As a result, the condition is often left without being recognized for too long.

What is MAS?

The term is often used to describe secondary hemophagocytic lymphohistio (HLH) and Macrophage activation syndrome (MAS) is the term that is utilized by rheumatologists to define the possibility of a life-threatening condition that can arise from chronic inflammatory diseases, more typically systemic juvenile arthritis (sJIA) as well as its adult counterpart, adult-onset Still disease.

The syndrome first was discovered in juvenile rheumatoid arthritis (JRA) patients, now referred to as JIA, or juvenile Idiopathic Arthritis (JIA)and with an large Kupffer cells (i.e. the stellate macrophages found in the liver) with astonishingly low levels of white blood cells as well as uncommonly low erythrocyte sludge rate (ESR) ( 1).

The subsequent literature reported the presence of activated macrophages, as well as hemophagocytic histiocytes among patients suffering from the rheumatic condition, which is known as reactive hemophagocytic disorder and later referred to as MAS ( 2- 4).

Macrophage activation syndrome (MAS)
Figure 02: Macrophage activation syndrome (MAS)

The phrase Macrophage Activation Syndrome (MAS) is a type of complication that could be fatal of rheumatic illnesses. The majority of cases occur as a result of systemic Juvenile Idiopathic Arthritis (sJIA) However, it could be present, though less frequently, in the context of systemic Lupus Erythematosus as well as Kawasaki disease.

MAS typically manifests as an increase in fever, lymphadenopathy, and hepatosplenomegaly varying in association with hemorrhages and liver-related signs. kidney and central nervous system involvement. It may also cause multiple organ failure. Laboratory abnormalities include a decrease in white blood cells, platelet and hemoglobin, hypertransaminasemia, a marked increase in ferritin, and evidence for intravascular coagulation activation.

Key Differences between HLH and MAS

Here are the key differences between HLH (Hemophagocytic Lymphohistiocytosis) and MAS (Macrophage Activation Syndrome):

  1. Underlying conditions and triggers:
    • HLH: Can be primary (genetic mutations) or secondary (infections, malignancies, autoimmune disorders, etc.).
    • MAS: Primarily associated with autoimmune disorders, particularly systemic juvenile idiopathic arthritis (sJIA).
  2. Primary affected cells:
    • HLH: Abnormal function of natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) is the primary defect.
    • MAS: Macrophages and T cells are primarily activated and contribute to the pathogenesis.
  3. Clinical context:
    • HLH: Can occur in individuals of any age, including children and adults, and is associated with various underlying conditions.
    • MAS: Mainly affects children and is commonly associated with sJIA or other autoimmune disorders.
  4. Presentation and symptoms:
    • HLH: Fever, hepatosplenomegaly, cytopenias, coagulopathy, and organ dysfunction are characteristic features.
    • MAS: High fever, rash, arthritis, hepatosplenomegaly, and potential organ involvement (e.g., liver dysfunction) are common manifestations.
  5. Diagnostic criteria:
    • HLH: Diagnosis is based on specific criteria, including genetic testing (for primary HLH) and laboratory markers such as ferritin levels, cytopenias, and evidence of Hemophagocytosis.
    • MAS: Diagnosis relies on clinical and laboratory findings, including elevated ferritin levels, liver enzyme abnormalities, and evidence of systemic inflammation.
  6. Treatment approaches:
    • HLH: Treatment typically involves immunosuppression, chemotherapy, and, in severe cases or primary HLH, hematopoietic stem cell transplantation (HSCT).
    • MAS: Treatment focuses on controlling the underlying autoimmune disease and includes immunosuppressive therapies such as corticosteroids, cyclosporine, and biologic agents.

It’s important to note that HLH and MAS can share overlapping features, and distinguishing between them can sometimes be challenging. Accurate diagnosis is crucial for appropriate management and improving patient outcomes. Medical professionals with expertise in these conditions should be involved in the diagnostic process and treatment decisions.

How is HLH Diagnosed?

HLH is so infrequent it is a mystery to many health professionals who do not recognize the symptoms. HLH could “look like” certain cancers at the beginning of the disease. This is why it’s common for the disease to be not diagnosed or is left untreated for a long time.

HLH cannot be identified by a blood test that is done in a clinical setting that is appropriate. The doctor may collect a small amount of blood from the shunt in which they sit and check for HLH within the brain. It is crucial to keep in mind that certain types of malignancies (including lymphoma and leukemia) may appear similar to HLH and, consequently, these disorders need to be examined thoroughly in the initial assessment of a patient suffering from HLH.

Doctors need to use these tests to determine if they have HLH and create a customized treatment strategy.

    • The blood tests are available in HTML0. This includes blood cell counts in addition to liver function studies, and indicators for activation of the immune system including ferritin and the IL-2 receptor’s soluble levels.
    • Bone biopsies and aspirates of bone marrow: Bone biopsies and aspirates of bone marrow (taking samples of the bone marrow in the patient’s body which is the organ responsible for making blood)
  • Lumbar puncture. Doctors use this technique to gather cerebrospinal fluid in order to determine if HLH has an effect on the brain.
  • Imaging studies. They can be X-rays, Computed tomography (CT) scans Ultrasound, or Magnetic image resonance (MRI).

How is MAS Diagnosed?

Macrophage Activation Syndrome, also known as Macrophage Activation Disorder (MAS), can be diagnosed via clinical, laboratory and histopathological findings. Specific criteria can vary slightly based on its underlying condition–for instance systemic juvenile idiopathic arthritis (SJIA) or another form of arthritis–while here are commonly-used criteria for diagnosing Macrophage Activation Syndrome:

  • Clinical Symptoms: Multiple Atrophy Syndrome is characterized by persistent or recurrent fever combined with systemic symptoms that include hepatosplenomegaly (an enlarged liver and spleen), lymphadenopathy (enlarged lymph nodes), rash, central nervous system dysfunction and hemorrhagic manifestations.
  • Laboratory Findings: Certain lab abnormalities contribute to diagnosing MAS. Examples are:
  • Cytopenias: Decrease in one or more blood cells types such as anemia (low red blood cells), leukopenia (low white blood cells), or thrombocytopenia (low platelets).
  • Elevated Ferritin Levels: Significantly elevated serum ferritin, a protein responsible for iron storage and associated with inflammation.
  •  Elevated Liver Enzymes: Elevated levels of liver enzymes such as Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST), may indicate damage in your liver.
  • Coagulopathy: refers to abnormalities in blood clotting ability, such as prolonged prothrombin time (PT) or activated partial thromboplastin time (aPTT).
  • Hypertriglyceridemia and Hypofibrinogenemia: Increased levels of triglycerides and decreased fibrinogen in the blood.
  • Hemophagocytosis: When activated macrophages engulf blood cells from bone marrow, spleen or lymph node environments through histopathological examination (a process confirmed through histopathological testing), histophagocytosis occurs.
  • Exclusion of other conditions: To properly diagnose MAS, one should rule out other potential conditions with similar symptoms and laboratory abnormalities that might also present themselves, including sepsis, malignancies or causes of secondary hemophagocytic lymphohistiocytosis (HLH).

Research and Advancements of HLH and MAS

Research and Advancements of HLH and MAS:

Genetic Studies: Researchers have made considerable headway in their efforts to identify genetic mutations associated with both HLH and MAS, such as mutations affecting perforin, syntaxin and Munc13-4 gene mutations which may contribute to this condition. Understanding such abnormalities has allowed doctors and specialists to better diagnose patients quickly as well as develop tailored therapies.

Biomarkers: Researchers have explored various biomarkers as tools in diagnosing and monitoring of HLH and MAS. Such biomarkers may include the soluble interleukin-2 receptor (sIL-2R), CD25 soluble antigen levels, ferritin levels, or cytokine profiles that help distinguish this syndrome from similar conditions while simultaneously measuring disease activity levels.

Treatment Strategies: Advancements have been made in treating both HLH and MAS. Hematopoietic stem cell transplantation (HSCT) remains the definitive curative therapy for primary HLH; corticosteroids, etoposide, and cyclosporine are among several immune-modulating agents that have demonstrated effectiveness at managing hyperinflammation while biologic therapies like anti-interleukin-1-antibodies-may offer hope in treating resistant cases of MAS.

Improved Diagnostic Criteria: Thanks to international collaboration efforts, new diagnostic criteria for HLH and MAS such as the HLH-2004 diagnostic guidelines have been created, giving clinicians clear guidance for accurate diagnoses.

Collaborative research networks: Different research networks such as the Histiocyte Society and Pediatric Rheumatology International Trials Organization (PRINTO), have been formed in order to facilitate multicenter studies and clinical trials, encouraging collaboration among researchers and clinicians worldwide in order to advance our knowledge and management of HLH and MAS.

Targeted Therapies: The discovery of specific molecular targets has opened the doors for targeted therapies in both HLH and MAS. Ruxolitinib, an inhibitor of Janus Kinase (JAK), has shown encouraging results in blocking cytokine signaling pathways associated with MAS.

Patient Registries and Databases: Patient registries and databases provide an ideal means of collecting and analyzing clinical data on HLH and MAS, making research easier, while helping clinicians gain a clearer understanding of disease patterns, treatment outcomes, and long-term follow-up. These resources contribute greatly towards progress.

Continued research and advancement in these areas can significantly enhance diagnosis, treatment and long-term outcomes for individuals living with HLH or MAS.

How Do Doctors Treat HLH?

It is crucial to get treatment promptly in patients suffering from HLH because the disease can be fatal. Initial treatments are usually utilized to decrease the level of inflammation that occurs in the body. They reduce the immune system, which assists in reducing the damage that is done to the body of a patient.

The treatment may consist of:

  • The combination of chemotherapy and steroids helps to cool down hyper-inflammation.
  • Antibody therapy that blocks certain inflammatory proteins or kills T cells that produce these proteins
  • The immune system is suppressed by medicines. system
  • Treatment of any infection that is present, and also to avoid the development of the spread of

If treated, HLH may come under the control of within a couple of weeks. But, it can be recurrently flare up, particularly because treatment levels are reduced, and the patient might require additional treatments.


HLH and MAS are two hyperinflammatory syndromes characterized by dysregulated immune responses and systemic inflammation, though there may be an overlap in terms of symptoms and clinical features between them. Although both disorders share some similarities when it comes to symptoms and treatment approaches, there are differences in their causes, underlying conditions, diagnostic criteria, clinical manifestations, and strategies used.

Significant advances have been achieved in research and understanding of HLH and MAS over recent decades, from genetic studies identifying mutations associated with these syndromes, leading to improved diagnosis and targeted therapies, biomarker discovery for diagnosis monitoring purposes as well as advances in treatments such as HSCT, immune-modulating agents, and biologic therapies.

Collaborative research networks, standard diagnostic criteria, and patient registries have promoted global cooperation while making multicenter studies and clinical trials possible. Their efforts have led to greater insight into disease patterns and treatment outcomes.

However difficulties remain in distinguishing HLH and MAS due to shared characteristics and symptoms; more research must be conducted in order to refine diagnostic criteria and develop more specific biomarkers.