What is the appropriate work‑up and initial management for a patient with suspected secondary hemophagocytic lymphohistiocytosis?

Secondary HLH Evaluation and Initial Management

For suspected secondary HLH, immediately initiate diagnostic workup using HLH-2004 criteria while simultaneously identifying and treating the underlying trigger—most commonly infection, malignancy, or autoimmune disease—and begin high-dose corticosteroids (methylprednisolone 1g IV daily for 3-5 days) without waiting for complete diagnostic confirmation if clinical suspicion is high. 1

Diagnostic Workup Algorithm

Core Laboratory Assessment (HLH-2004 Criteria)

Diagnosis requires at least 4 of the following 8 criteria (validated sensitivity 86.5%, specificity 86.1%): 2

• Fever >38.5°C – nearly universal, persistent and unremitting 1
• Splenomegaly – characteristic but may be absent in some secondary forms 1
• Cytopenias affecting ≥2 cell lines (hemoglobin <9 g/dL, platelets <100×10⁹/L, neutrophils <1.0×10⁹/L) 1
• Hypertriglyceridemia (fasting triglycerides ≥3.0 mmol/L or ≥265 mg/dL) and/or hypofibrinogenemia (≤1.5 g/L) 1
• Hemophagocytosis in bone marrow, spleen, or lymph nodes – present in only 51-60% at initial presentation, so absence does not exclude HLH 1
• Low or absent NK cell activity – specific for HLH, normally preserved in other inflammatory conditions 1
• Ferritin ≥500 μg/L – levels >5,000-10,000 μg/L are highly suggestive; ferritin has 94% sensitivity as a screening marker 1, 2
• Soluble CD25 (sCD25) ≥2,400 U/mL – AUC 0.90 for adult HLH diagnosis, outperforming ferritin 1

Critical pitfall: Do not delay empirical treatment while awaiting all criteria if ferritin >10,000 μg/L with progressive cytopenias and persistent fever despite appropriate antimicrobials. 1

Alternative Diagnostic Tool: HScore

An HScore >169 confers >93% probability of HLH (sensitivity 82.4%, specificity 87.6%), while a score of 90-168 indicates 75-93% probability. 1, 2 The HScore integrates underlying immunosuppression, temperature, organomegaly, number of cytopenias, ferritin, triglycerides, fibrinogen, AST, and hemophagocytosis. 1

Identifying the Underlying Trigger

Infection Workup (Most Common Trigger)

Viral pathogens dominate, particularly: 3

• EBV serology and EBV DNA PCR – EBV is the most frequent viral trigger; levels >10³ copies/mL are relevant for EBV-HLH development 3
• CMV serology and CMV DNA PCR – second most common viral trigger 3
• HIV testing – essential in all cases 3
• Influenza PCR during appropriate season 3
• Blood cultures to exclude bacterial sepsis 4
• Fungal markers (beta-D-glucan, galactomannan) in immunosuppressed patients 3

Malignancy Screening (Second Most Common Trigger)

Lymphoma-associated HLH is the major cause of malignancy-triggered HLH, with the worst prognosis of all HLH subgroups: 3

• Peripheral blood and bone marrow examination for blasts and atypical lymphocytes 3
• Flow cytometry on peripheral blood and bone marrow for lymphoma immunophenotyping 3
• CT chest/abdomen/pelvis to identify lymphadenopathy or organomegaly 3
• PET imaging in cases with high suspicion for occult lymphoma 3
• Lymph node or tissue biopsy of any suspicious lesions 3

T-cell and NK-cell lymphomas carry highest HLH association, followed by B-cell lymphomas and Hodgkin lymphoma. 4 Regional variation exists with increased NK/T-cell and EBV-triggered lymphoma in Asia. 3

Autoimmune/Autoinflammatory Assessment

• ANA, anti-dsDNA, complement levels for systemic lupus erythematosus 1
• Ferritin glycosylation (<20% glycosylated fraction suggests adult-onset Still's disease) 1
• Review for macrophage activation syndrome (MAS) in patients with known systemic juvenile idiopathic arthritis or adult-onset Still's disease 1

Genetic Testing Considerations

Flow cytometry for NK/T-cell degranulation and protein expression (perforin, SAP) should be considered in: 3

• Young adults with unexplained HLH
• Male patients with lymphoma and EBV-driven HLH (24% of XLP1 patients develop malignancy) 4
• Family history of HLH or early-onset lymphoma 3

Distinguishing Malignancy-Triggered HLH from HLH During Chemotherapy

This distinction is critical because therapeutic approaches differ markedly: 3

• Malignancy-triggered HLH presents at diagnosis or relapse of malignancy; requires aggressive HLH-directed therapy plus malignancy treatment 3
• HLH during chemotherapy develops during/after treatment while patients are often in remission; typically infection-triggered due to immunosuppression; requires conservative approach with corticosteroids ± IVIG, sparing etoposide to allow bone marrow recovery 3

Key differentiating features: Unduly prolonged cytopenias after chemotherapy, persistent fever despite antibiotics, and presence of other HLH parameters suggest HLH during chemotherapy. 3

Initial Management Strategy

Immediate Interventions

High-dose corticosteroids are the cornerstone of first-line treatment: 1

• Methylprednisolone 1g IV daily for 3-5 consecutive days OR
• Dexamethasone 5-10 mg/m² daily 3

Simultaneously treat the underlying trigger: 1

• Antimicrobials for infection-triggered HLH (continue/initiate pathogen-specific therapy)
• Chemotherapy for malignancy-associated HLH
• Disease-modifying therapy for autoimmune-triggered HLH/MAS

Supportive Care and Prophylaxis

• Broad antimicrobial prophylaxis against Pneumocystis jirovecii and fungi in patients requiring HLH-directed immunosuppression 3
• Antiviral prophylaxis due to severe T-cell depletion 3
• HEPA-filtered air hospitalization should be considered 3
• Transfusion support for severe cytopenias 1

Second-Line Therapies for Inadequate Response

If corticosteroids fail to control hyperinflammation within 48-72 hours: 1

• Cyclosporine A (or tacrolimus with careful drug level monitoring) 3, 1
• Anakinra (IL-1 receptor antagonist) – particularly effective in MAS 1
• Tocilizumab (anti-IL-6) – especially for CAR T-cell-induced HLH/MAS 1
• Rituximab 375 mg/m² weekly for 2-4 doses in EBV-triggered HLH to clear B-cell viral reservoir 3

Etoposide: Use with Caution

Etoposide-based therapy (HLH-94 protocol) should be reserved for: 3, 1

• Rapid clinical deterioration in treatment-naive patients
• Refractory disease despite corticosteroids and second-line agents
• Malignancy-triggered HLH requiring aggressive immunosuppression

Avoid etoposide in HLH during chemotherapy because bone marrow recovery is central for immune reconstitution. 3

Monitoring and Reassessment

Serial monitoring every 12-24 hours of: 1

• Ferritin (rapid rise is key dynamic marker)
• Complete blood counts
• Triglycerides and fibrinogen
• Liver function tests
• sCD25 if initially elevated
• Pathogen-specific markers (EBV DNA, CMV DNA)

Weekly reevaluation of need for continued intensive immunosuppression. 3

Critical Pitfalls to Avoid

• Delayed diagnosis significantly increases mortality – maintain high index of suspicion in patients with persistent fever, cytopenias, and ferritin >5,000 μg/L 1
• Do not wait for hemophagocytosis – absent in up to 49% of initial bone marrow aspirates 1
• Do not overlook underlying triggers – comprehensive infectious and malignancy workup is mandatory 1
• Do not apply pediatric protocols directly to adults – dose adjustments and different considerations required 1
• Do not delay ICU transfer in patients with grade ≥2 organ dysfunction, shock, platelets <30 g/L, or severe neurotoxicity 1

Prognosis

Mortality in adult HLH ranges 20-88%, primarily from refractory HLH, secondary infections, and progression of underlying disease. 3 Malignancy-associated HLH has the worst prognosis of all HLH subgroups. 3 Early recognition and prompt treatment are essential to prevent irreversible organ damage. 1, 5