Diagnostic and Treatment Parameters for Hemophagocytic Lymphohistiocytosis (HLH)

Diagnostic Considerations

The diagnosis of HLH requires a combination of specific clinical and laboratory parameters, with treatment decisions based on disease severity, underlying triggers, and patient age 1, 2
The HLH-2004 criteria serve as the primary diagnostic framework for HLH in all age groups, despite having substantial weaknesses in malignancy contexts 1, 3
Diagnosis requires either molecular diagnosis consistent with HLH (genetic testing) or fulfillment of 5 of the 8 following criteria, including fever, splenomegaly, cytopenias, hypertriglyceridemia, hemophagocytosis, low or absent NK cell activity, elevated ferritin, and elevated soluble CD25 1, 2, 3, 4
Hemophagocytosis alone is neither sensitive nor specific for HLH and may be present in other conditions like septicemia 1, 3

Cytopenias affecting ≥2 cell lines are a key laboratory criterion for HLH 2, 3
Hypertriglyceridemia (≥265 mg/dL) and/or hypofibrinogenemia (≤150 mg/dL) are also important laboratory criteria 3
Hemophagocytosis in bone marrow, spleen, lymph nodes, or liver is a critical diagnostic finding 2, 4
Low or absent NK cell activity is a key immunological criterion for HLH 4
Elevated ferritin (≥500 ng/mL) is a common laboratory finding in HLH 3
Elevated soluble CD25 (≥2400 U/mL) is also a key laboratory criterion for HLH 4

Treatment of underlying malignancy is essential in malignancy-associated HLH 6
The HLH-94 protocol with etoposide and corticosteroids is commonly used in malignancy-associated HLH 6, 7
T-cell lymphoma-associated HLH has a worse prognosis than B-cell lymphoma-associated HLH 7, 6
Consider stem cell transplantation as consolidation in patients with hematologic malignancy-associated HLH 7, 6

Survival rates for malignancy-associated HLH are generally poor, with 30-day survival rates of 56-70% and median overall survival of 36-230 days 7, 6
T-cell lymphoma-associated HLH has a worse prognosis than B-cell lymphoma-associated HLH 7, 6
For pediatric patients with malignancy-associated HLH, the survival rate following the acute phase is 56%, and the 5-year survival rate is 36% 7, 6

Malignancy as an HLH trigger correlates strongly with age, with 68% of patients over 60 years having malignancy-associated HLH 1, 8
In children and adolescents, malignancy accounts for only 8% of HLH cases 1, 8