The Decimating Army: Hemophagocytic Lymphohistiocytosis as the Initial Presentation of Adult-Onset Still's Disease.

Hemophagocytic lymphohistiocytosis (HLH) is a rare and often missed presentation in the hospital setting. It is a hyperinflammatory syndrome of immune activation and dysregulation characterized by fever, cytopenias, elevated serum ferritin levels, and hepatosplenomegaly. It has a multifactorial etiology occurring primarily secondary to infection, malignancy, immune checkpoint inhibitors, or autoimmune disease. HLH that occurs in autoimmune diseases such as adult-onset Still's disease and systemic lupus erythematosus is referred to as macrophage activation syndrome. However, it may rarely be a primary disorder from a genetic defect. The pathophysiology of HLH is poorly understood and often results in multiorgan dysfunction. We present an older adult male patient with several hospital stays due to his symptoms, who presented with lethargy, low-grade fever, cough, dyspnea, and recurrent pleural effusions. He had bicytopenia, elevated ferritin, and hypertriglyceridemia. The diagnosis of HLH may be delayed, especially in older adult patients with an insidious course, and requires a high index of suspicion.