Hemophagocytic Lymphohistiocytosis (HLH) is a rare disorder of the immune system primarily affecting young infants and children, although it can develop for the first time at any age. According to a large population-based study published in Sweden, it was estimated to occur in 1.2 cases per million.
HLH is often referred to as either the “primary” form which is hereditary, or the “secondary” form associated with infections, viruses, autoimmune diseases and malignancies (or cancers).
The primary form of HLH is also known as familial hemophagocytic lymphohistiocytosis (FHLH or FHL). It occurs when defective genes are inherited from either both parents (autosomal recessive) or from the mother alone. Since 1999, five genes have been identified which correspond with five types of autosomal recessive HLH.
Secondary HLH is often diagnosed in older patients, and there is no family history associated with this form of disease. It is not known to be caused by, but may be associated with vaccinations, viral infections such as Epstein-Barr, cytomegalovirus (CMV), herpes virus and other underlying diseases.
Treatment of HLH/FHL can include a combination of chemotherapy, immunotherapy and steroids. Antibiotics and antiviral drugs may also be used.
These treatments may be followed by a bone-marrow or stem-cell transplant in patients with persistent or recurring HLH or those with FHL.
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