Macrophage activation syndrome (MAS) is a term used by rheumatologists to describe a form of secondary haemophagocytic lymphohistiocytosis (HLH) in association with chronic rheumatic diseases of childhood. It occurs most commonly with systemic-onset juvenile rheumatoid arthritis (SoJRA), but has also been reported with other rheumatic diseases. MAS manifestations may be seen at the onset of the rheumatic disease, during periods of active disease or even when the underlying rheumatic disease is quiescent.

Historical perspective and issues with nomenclature

The earliest description of MAS in the paediatric rheumatology literature may be the report of deaths from hepatic failure in patients with SoJRA at the first American Rheumatism Association(ARA) conference on rheumatic diseases of childhood (Boone, 1977). In 1983, Silverman described seven patients with ‘consumptive coagulopathy’ in children with SoJRA, either following the second dose of intramuscular gold or in the face of active disease (Silverman et al., 1983). The prominent clinical feature seen was a coagulopathy resembling disseminated intravascular coagulation (DIC), which most likely was a manifestation of secondary HLH. Subsequently, Jacobs reported five children (four with SoJRA, one with polyarticular juvenile rheumatic arthritis (JRA)) with a fatal outcome from a similar coagulopathy following the second gold injection (Jacobs et al., 1984). Hadchouel in 1985 described seven patients with SoJRA who developed a clinical syndrome characterized by haemorrhagic and neurological manifestations and hepatic, haematological and metabolic derangements (Hadchouel et al., 1985).