How is macrophage activation syndrome (MAS) diagnosed?

Updated: Nov 21, 2018
  • Author: Angelo Ravelli, MD; Chief Editor: Lawrence K Jung, MD  more...
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The recognition that macrophage activation syndrome (MAS) is clinically similar to HLH has led many clinicians to use the diagnostic guidelines for hemophagocytic lymphohistiocytosis (HLH) in the diagnosis of macrophage activation syndrome. [31] However, the use of HLH criteria in patients with macrophage activation syndrome is associated with several problems; the chief problem is the requirement for tissue confirmation. A 2014 retrospective analysis concluded that HLH-2004 guidelines are likely not appropriate for identification of MAS in children with systemic juvenile idiopathic arthritis (SJIA), and that preliminary MAS guidelines showed the strongest ability to identify MAS in SJIA. [32]

The pathognomonic feature of the syndrome is bone marrow examination that reveals numerous well-differentiated macrophages actively phagocytosing hematopoietic cells. Such cells may be found in various other organs as well and may account for many of the systemic manifestations. However, in patients with HLH and macrophage activation syndrome, the bone marrow aspirate sample does not always reveal hemophagocytosis. [33] Furthermore, hemophagocytosis is not always demonstrable at onset. In HLH, hemophagocytosis may be detected more frequently in liver, lymph node, or splenic biopsy samples than in bone marrow samples. However, performing a biopsy of these organs is contraindicated in children with macrophage activation syndrome in the presence of intravascular coagulopathy. Moreover, the failure to document hemophagocytosis does not exclude the diagnosis of HLH. A 2014 study concluded that hyperinflammation, rather than hemophagocytosis, is the common link between macrophage activation syndrome andhemophagocytic lymphohistiocytosis. [34] These problems emphasize the need to identify criteria that obviate the need for tissue diagnosis.

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