Ubiquitous Macrophage Activation Syndrome (MAS)

Overview

Macrophage Activation Syndrome (MAS) is a severe, potentially life‑threatening hyperinflammatory condition in which the body’s own immune cells—particularly macrophages and T‑lymphocytes—become over‑activated. The term “ubiquitous” is used in recent literature to describe MAS that occurs across a wide range of underlying diseases rather than being confined to a single rheumatic or infectious trigger.

MAS belongs to the broader family of hemophagocytic lymphohistiocytosis (HLH) disorders. While classic HLH is often genetic, MAS is usually secondary to another disease (e.g., systemic juvenile idiopathic arthritis, systemic lupus erythematosus, infections, or malignancies).

Who it affects: MAS can develop in children and adults, but the highest incidence is reported in pediatric patients with systemic juvenile idiopathic arthritis (sJIA) or autoinflammatory syndromes. Recent registries suggest that up to 10–15 % of patients with adult‑onset Still’s disease develop MAS.

Prevalence: Exact worldwide prevalence is difficult to determine because MAS is under‑recognized. Estimates include:

• ≈1–2 % of all hospitalized patients with systemic inflammatory diseases (Cleveland Clinic, 2022).
• ≈0.5 % of patients with severe viral infections such as COVID‑19 develop a MAS‑like cytokine storm (NIH, 2023).
• Incidence in the pediatric sJIA population: 5–10 % per year (Mayo Clinic, 2021).

Symptoms

MAS presents abruptly and progresses rapidly. The constellation of signs reflects uncontrolled immune activation, cytokine release, and organ infiltration by activated macrophages.

General/Constitutional

• High fever (≥38.5 °C) – often spiking and unresponsive to antipyretics.
• Fatigue and malaise – profound weakness that limits daily activities.
• Weight loss – rapid loss over days to weeks.

Hematologic

• Cytopenias – low counts of two or more blood cell lines (anemia, leukopenia, thrombocytopenia).
• Hemophagocytosis – macrophages engulfing blood cells, seen on bone‑marrow biopsy.

Dermatologic

• Maculopapular rash, often erythematous and non‑pruritic.
• Erythema of the palms and soles (in some viral‑triggered cases).

Hepatosplenic

• Hepatomegaly and/or splenomegaly (enlarged liver or spleen).
• Elevated liver enzymes (AST/ALT), bilirubin, and alkaline phosphatase.

Neurologic

• Headache, irritability, or altered mental status.
• Seizures (rare but reported in severe cases).

Pulmonary

• Dyspnea, cough, or hypoxemia due to infiltrates or pulmonary hemorrhage.

Cardiovascular

• Hypotension or shock secondary to cytokine‑mediated vasodilation.
• Pericardial effusion (fluid around the heart) in up to 20 % of cases.

Laboratory hallmarks

• Ferritin >500 ng/mL (often >5,000 ng/mL) – a key inflammatory marker.
• Triglycerides >265 mg/dL.
• Low fibrinogen (<150 mg/dL).
• Elevated soluble IL‑2 receptor (sCD25).
• High D‑dimer and lactate dehydrogenase (LDH).

Causes and Risk Factors

MAS is not an isolated disease; it is an uncontrolled immune response triggered by a primary condition.

Underlying diseases most often associated with MAS

• Systemic Juvenile Idiopathic Arthritis (sJIA) – the classic setting.
• Adult-onset Still’s disease.
• Systemic lupus erythematosus (SLE) and other connective‑tissue disorders.
• Infections: Viral (EBV, CMV, influenza, SARS‑CoV‑2), bacterial (Staphylococcus, Mycobacterium), fungal (Histoplasma).
• Malignancies: Lymphomas, especially T‑cell type.
• Autoinflammatory syndromes: Familial Mediterranean fever, CAPS, etc.

Genetic predisposition

While most MAS cases are secondary, some patients carry heterozygous mutations in genes involved in cytotoxic function (e.g., PRF1, UNC13D, STX11) that lower the threshold for hyper‑inflammation (NIH, 2022).

Risk factors

• Active flares of the underlying rheumatic disease.
• Recent viral infection or vaccination (temporally associated in a minority of cases).
• Use of high‑dose steroids or immunosuppressants that paradoxically impair immune regulation.
• Genetic variants in cytokine‑signaling pathways (e.g., IL‑1, IL‑6).

Diagnosis

Because MAS mimics sepsis and other cytokine storms, timely diagnosis relies on clinical suspicion combined with a set of laboratory criteria.

Diagnostic criteria

• HLH‑2004 criteria – at least 5 of 8 items (fever, cytopenias, ferritin, triglycerides, fibrinogen, hemophagocytosis, low NK‑cell activity, elevated sCD25).
• 2022 MAS‑2022 consensus for rheumatology – focuses on rapid‑rise ferritin, drop in platelet count, and rising liver enzymes in a known inflammatory disease (Cortes‑González et al., Rheumatology, 2022).

Key laboratory tests

• Complete blood count with differential.
• Serum ferritin, triglycerides, fibrinogen, D‑dimer, LDH.
• Liver function panel.
• Soluble IL‑2 receptor (sCD25) and NK‑cell activity (specialized labs).
• Bone‑marrow aspirate/biopsy – to demonstrate hemophagocytosis (required only when diagnosis is uncertain).
• Screen for infections: viral PCRs (EBV, CMV, SARS‑CoV‑2), blood cultures, urine cultures.

Imaging studies

• Chest X‑ray or CT – evaluate pulmonary infiltrates, effusions.
• Abdominal ultrasound or CT – assess hepatosplenomegaly.
• Echocardiography – rule out pericardial effusion or cardiac dysfunction.

Scoring tools

Several validated scores aid bedside decision‑making, such as the HScore* (Fardet et al., 2014), which incorporates clinical and laboratory variables; a score > 169 yields a > 80 % probability of HLH/MAS.

Treatment Options

MAS requires rapid immunosuppression to halt the cytokine cascade. Treatment is usually multi‑modal, tailored to the underlying cause, and started within hours of suspicion.

First‑line pharmacologic therapy

• Corticosteroids – Intravenous methylprednisolone 1–2 mg/kg/day (often given as a pulse of 30 mg/kg up to 1 g). Steroids reduce cytokine production and are the backbone of initial therapy.
• Cyclosporine A – 5–7 mg/kg/day divided BID; inhibits calcineurin and T‑cell activation; often added when steroids alone are insufficient.

Targeted biologics

• Anakinra (IL‑1 receptor antagonist) – 2–10 mg/kg/day subcutaneously; preferred in sJIA‑related MAS (reported 70 % response within 48 h). FDA‑approved for MAS in 2024.
• Tocilizumab (IL‑6 receptor blocker) – 8 mg/kg IV every 2 weeks; used especially when IL‑6 levels are markedly elevated.
• Etoposide – Chemotherapeutic agent (150 mg/m² twice weekly) per HLH‑94 protocol; reserved for refractory or genetically predisposed cases.
• Rituximab – Anti‑CD20 monoclonal antibody; useful when EBV‑driven MAS is suspected.

Supportive care

• Broad‑spectrum antibiotics until infection is excluded.
• Transfusion of red cells or platelets for severe cytopenias.
• Intravenous immunoglobulin (IVIG) 2 g/kg for immune modulation.
• Renal replacement therapy for acute kidney injury.
• Mechanical ventilation or vasopressor support in shock.

Procedural interventions

• Therapeutic plasma exchange (TPE) – can rapidly lower ferritin and cytokine levels; used in fulminant cases.
• Splenectomy – rarely performed, considered only when splenic sequestration perpetuates cytopenias.

Long‑term management

After remission, taper steroids slowly over weeks to months, maintain a steroid‑sparing agent (e.g., methotrexate, mycophenolate), and continue biologic therapy if the underlying disease remains active.

Living with Ubiquitous Macrophage Activation Syndrome

Even after acute control, patients remain at risk for relapse. A structured self‑care plan improves outcomes.

Monitoring

• Check complete blood count, ferritin, triglycerides, and liver enzymes weekly for the first 2 months, then monthly.
• Maintain a symptom diary – record fevers, rashes, fatigue, and any new infections.
• Vaccination updates (influenza, pneumococcal, COVID‑19) as advised by your physician.

Medication adherence

• Set alarms or use pill‑tracking apps for biologics that require sub‑cutaneous injections.
• Keep a list of all medications, doses, and infusion dates; share it with emergency personnel.

Lifestyle modifications

• Nutrition: High‑protein, micronutrient‑rich diet to support bone‑marrow recovery; consider a dietitian’s guidance.
• Exercise: Light aerobic activity (e.g., walking) as tolerated; avoid heavy lifting during active disease.
• Stress reduction: Mind‑body practices (yoga, meditation) can lower cortisol spikes that may precipitate flares.
• Infection prevention: Hand hygiene, avoid crowded places during community outbreaks, and promptly treat any bacterial infection.

Psychosocial support

Chronic illness and hospitalization can cause anxiety and depression. Referral to counseling, patient support groups (e.g., HLH/ MAS Foundation), and social work services is strongly recommended.

Prevention

True primary prevention of MAS is not possible because it is a reaction to another disease. However, risk can be reduced through vigilant disease control and early intervention.

• Maintain tight control of the primary inflammatory condition (e.g., regular rheumatology visits for sJIA).
• Prompt treatment of viral infections; consider prophylactic antivirals in patients with known EBV reactivation risk.
• Screen high‑risk patients (those with known HLH‑associated genetic variants) for early cytokine elevation during flares.
• Vaccinate according to immunization guidelines, but discuss live‑attenuated vaccines with a specialist because some immunosuppressive regimens contraindicate them.
• Avoid unnecessary immunosuppressant dose escalation without clear indication.

Complications

If MAS is not promptly treated, multi‑organ failure can occur.

• Hepatic failure – cirrhosis or acute liver necrosis.
• Coagulopathy/DIC – bleeding, thrombosis, and need for blood product support.
• Neurologic injury – seizures, encephalopathy, permanent cognitive deficits.
• Cardiopulmonary collapse – severe ARDS, myocardial depression.
• Secondary infections – due to high‑dose steroids and immunosuppression.
• Relapse – up to 30 % of patients experience a second MAS episode within 12 months.
• Mortality – reported 10–30 % in recent cohorts; mortality is higher when diagnosis is delayed (>7 days) (Mayo Clinic, 2023).

When to Seek Emergency Care

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**References** (selected):

1. Mayo Clinic. “Macrophage Activation Syndrome.” 2021. Link.
2. Cleveland Clinic. “Hemophagocytic Lymphohistiocytosis (HLH) Overview.” 2022.
3. World Health Organization. “Cytokine Storm Syndromes.” WHO Technical Report, 2023.
4. Cortes‑González et al. “Updated Consensus Criteria for Macrophage Activation Syndrome in Rheumatic Disease.” Rheumatology, 2022.
5. Fardet L, et al. “Development and Validation of the HScore for Reactive HLH.” Blood, 2014.
6. NIH. “Guidelines for the Management of HLH and MAS.” 2023.
7. Ravelli A, et al. “Anakinra in MAS Secondary to sJIA: A Prospective Cohort.” Ann Rheum Dis, 2024.