Hemophagocytic lymphohistiocytosis: a rare diagnosis, an even rarer opportunity to appraise our understanding of the immune system

The syndrome identified as hemophagocytic lymphohistiocytosis (HLH) poses a rather difficult challenge to the physician. HLH was initially described as a familial disorder,1 which was later associated with various genetic defects that affect the cytotoxic machinery of CD8+ T and NK cells,2 but it also occurs sporadically, usually prompted by infections, rheumatic disorders, or neoplasia.3 Although its diagnostic criteria are established, its clinical presentation overlaps with many different conditions, requiring an enhanced awareness of the attending physician in order to reach the diagnosis and to initiate treatment early enough