Macrophage Activation Syndrome Upon Initiation of Adalimumab in a Patient With Longstanding Rheumatoid Arthritis.

Macrophage activation syndrome (MAS) is a subset of hemophagocytic lymphohistiocytosis (HLH) described in patients with rheumatological disorders. Some triggers of MAS and HLH include infection, malignancy, rheumatological disease, HIV, and rarely medications such as immunosuppressants. In recent medical literature, biologic agents are increasingly recognized as a potential trigger, but the mechanism behind this remains poorly understood. We describe the case of a patient who developed MAS after initiating adalimumab and propose a potential pathophysiological link between biologics and this syndrome.