The symptoms of the primary and secondary forms of hemophagocytic lymphohistiocytosis (HLH) include:
- Persistent fever, often high. Sometimes a microbial (often viral) cause is found, but this is common as a trigger of HLH/FHL.
- Abnormal blood tests such as a) low red blood cells, b) low platelets, and c) low neutrophils.
- Other blood abnormalities (liver dysfunction, elevated triglycerides, low sodium level, and low albumin level).
- Enlarged spleen.
- Skin rash, variable (30% of patients).
- Enlarged lymph nodes.
Combined with evidence of immunologic dysfunction:
- Decreased NK-cell function.
- Increased T-cell activation as evidenced by increased sIL2ra (soluble IL-2 receptor alpha) in the blood.
- Increased histiocyte activation as evidenced by increased ferritin.
CNS (central nervous system) involvement occurs in 50% of patients and may be present at the time of disease onset, or it can develop later.
A wide variety of symptoms of CNS disease include:
- Low or abnormally increased muscle tone.
- Difficulty with coordination.
- Weakness of face/eye nerves.
- Sudden blindness.
- Paralysis and coma (very rare).
On bone marrow examination, an abnormality in which histiocytes are “eating” other blood cells (also known as hemophagocytosis) can be detected. When prominent, this is a very useful diagnostic marker. Although the disease was named after this phenomenon, this symptom may be absent at onset or even throughout the course of the disease.
The Histiocyte Society has created diagnostic guidelines and recommendations concerning the treatment of HLH. The HLH-2004 research study, scheduled to conclude at the end of 2011, is to be used only at institutions with IRB (Institutional Review Board) approval and appropriate informal patient/family consent. The Histiocyte Society recommends the use of the HLH-94 treatment in conjunction with HLH-2004 diagnostic criteria as the standard of care until further analysis/publications recommend otherwise.