Differential diagnosis
The differential diagnosis of HLH includes secondary HLH and macrophage-activation syndrome or other primary immunodeficiencies that present with hemophagocytic lymphohistiocytosis, such as X-linked lymphoproliferative disease.Other conditions that may be confused with this condition include autoimmune lymphoproliferative syndrome. As a syndrome of intense inflammation it needs to be differentiated from sepsis, which may be extremely challenging.The diagnosis of acquired, or secondary, HLH is usually made in association with infection by viruses, bacteria, fungi, or parasites or in association with lymphoma, autoimmune disease, or metabolic disease. Acquired HLH may have decreased, normal, or increased NK cell activity. Griscelli syndrome
A major differential diagnosis of HLH is Griscelli syndrome (type 2). This is a rare autosomal recessive disorder characterized by partial albinism, hepatosplenomegaly, pancytopenia, hepatitis, immunologic abnormalities, and lymphohistiocytosis. Most cases have been diagnosed between 4 months and 7 years of age, with a mean age of about 17 months.Three types of Griscelli syndrome are recognised: type 1 has neurologic symptoms and mutations in MYO5A. Prognosis depends on the severity of neurologic manifestations. Type 2 has mutations in RAB27A and haemophagocytic syndrome, with abnormal T-cell and macrophage activation. This type has a grave prognosis if untreated. Type 3 has mutations in melanophilin and is characterized by partial albinism. This type does not pose a threat to those so affected. Treatment
In secondary cases, treatment of the cause, where possible, is indicated. Additionally, treatment for HLH itself is usually required.While optimal treatment of HLH is still being debated, current treatment regimes usually involve high dose corticosteroids, etoposide and cyclosporin.
Laboratory findings may include elevated triglyceride levels, low fibrinogen levels, transaminitis, and elevated ferritin levels (among others). Causes
Primary HLH is caused by loss of function, (i.e. inactivating) mutations in genes that code for proteins cytotoxic T cells and NK cells use to kill targeted cells, such as those infected with pathogens like the Epstein-Barr virus (EBV) or the Dengue virus. These mutations include those in the following genes: UNC13D, STX11, RAB27A, STXBP2, LYST, PRF1 1, SH2D1A, BIRC4, ITK, CD27, and MAGT1.Secondary HLH (sHLH) is associated with, and thought to be promoted by, malignant and non-malignant diseases that likewise weaken the ability of the immune system to attack EBV-infected cells. Malignant disorders associated with secondary HLH include T-cell lymphoma, B-cell lymphoma, acute lymphocytic leukemia, acute myeloid leukemia, and myelodysplastic syndrome. Non-malignant disorders associated with secondary HLH include: autoimmune disorders such as juvenile idiopathic arthritis, juvenile Kawasaki disease, systemic lupus erythematosus, the juvenile onset and adult onset forms of Stills disease, and rheumatoid arthritis; immunodeficiency disorders such as severe combined immunodeficiency, DiGeorge syndrome, Wiskott–Aldrich syndrome, ataxia–telangiectasia, and dyskeratosis congenita); and infections caused by EBV, cytomegalovirus, HIV/AIDS, bacteria, protozoa, fungi and SARS-CoV-2. Secondary HLH may also result from iatrogenic causes such as bone marrow or other organ transplantations; chemotherapy; or therapy with immunosuppressing agents;About 33% of all HLH cases, ~75% of Asian HLH cases, and nearly 100% of HLH cases caused by mutations in SH2D1A (see X-linked lymphoproliferative disease type 1) are associated with, and thought triggered or promoted by, EBV infection.