Which histologic findings are characteristic of macrophage activation syndrome (MAS)?

Updated: Nov 21, 2018
  • Author: Angelo Ravelli, MD; Chief Editor: Lawrence K Jung, MD  more...
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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 macrophage activation syndrome, the bone marrow aspirate does not always show hemophagocytosis. Moreover, failure to reveal hemophagocytosis does not exclude the diagnosis of macrophage activation syndrome.

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