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Primary hemophagocytic lymphohistiocytosis (HLH) is a rare genetic disease characterized by life-threatening inflammatory symptoms. Though primary HLH can affect adults and teenagers, the majority of patients are very young children—often in the first months or years of their lives. Due to the rapidly progressive nature of the disease, immediate therapy is required to temper the “cytokine storm”—a massive release of cytokines that leads to the signs and symptoms of primary HLH. Fewer than 100 cases of primary HLH are diagnosed in the US each year.1-5
Primary HLH presents as a heterogeneous syndrome of rapidly progressive, life-threatening inflammatory symptoms, including1,3:
To date, general consensus in the scientific community on primary HLH is as follows1:
| PRIMARY HLH | |
|---|---|
| Mortality rate | High mortality rate |
| Clinical presentation | Heterogeneous |
| Age of presentation | Typically infants/early childhood; documented cases also exist in teens and adults |
| Cause | Testable genetic mutation |
| Family history | May be positive for the disease |
| Recurrence | Likely |
| Resolution | Usually requires hematopoietic stem cell transplant (HSCT) |
The symptoms of primary HLH, along with their differing levels of severity, combine to form a broad spectrum of disease presentation that varies from patient to patient and within the same patient over time. Historically, a primary HLH diagnosis has been based on a genetic test or fulfillment of 5 of the 8 HLH-2004 criteria. These criteria include the HLH-1994 criteria, plus the addition of ferritin, low NK cells, and SIL2R.2,3,6-8
In 1994, as part of the HLH-94 clinical trial, the Histiocyte Society proposed a standard definition of HLH. Click to expand this version.
While the HLH-2004 criteria are useful for detecting common symptoms of HLH, ancillary testing and flow cytometric screening go beyond these criteria and help differentiate between primary and secondary HLH. This approach helps find the triggers or underlying causes of HLH and prevents misdiagnosis.9,10
Consider running the following tests9:
Consider checking for decreased levels of9,10:
IFNγ is central to the cytokine "storm"—an uncontrolled release of inflammatory cytokines and overactivation of phagocytes that give the syndrome its name.11
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