How I Treat How I treat hemophagocytic lymphohistiocytosis in the adult patient

Hemophagocytic lymphohistiocytosis (HLH) is a rare and devastating disorder of uncontrolled immune activation that has gained increasing recognition over the past decade. Patients with HLH present with clinical and laboratory evidence of extreme inflammation. This syndrome was first described in 1939 by Scott and Robb-Smith and again in 1952 when Farquhar and Claireaux reported a case of 2 infant siblings with progressive and fatal cytopenias, hepatosplenomegaly, and feverswith autopsy showing hemophagocytosis. This same constellation of symptoms has been subsequently described in both the pediatric and adult populations. In recent years, HLH has attracted growing attention due to an apparent inexplicable rise in the incidence of the disorder. The incidence of HLH in pediatrics is estimated as 1 to 225 per 300 000 live births and varies by geographic region. Although the incidence in the adult population is unknown, the number of cases reported in the literature has dramatically increased over the past 10 years. HLH is categorized as primary (familial) or secondary (acquired). Primary HLH is caused by genetic mutations affecting the cytotoxic function of T lymphocytes and natural killer (NK) cells and typically presents in young children. Secondary (acquired) HLH occurs in the setting of infectious, malignant, rheumatologic, or metabolic conditions. Occasionally, an inciting event is not identified and HLH is considered idiopathic. Although these entities are classically felt to be distinct, there is support for the idea that many patients with HLH have an underlying genetic predisposition. Although the causes, clinical presentation, and appropriate treatment of HLHmay be different in the older age group, our understanding of HLH in the adult setting derives primarily from research in pediatrics. This review highlights 3 cases of adult HLH and discusses a clinical approach to this illness in adults.