Ankylosing spondylitis presenting with macrophage activation syndrome.

Macrophage activation syndrome (MAS), which can also be considered as reactive hemophagocytic syndrome (HPS), is a rare and potentially fatal complication of rheumatic diseases. We describe a 42-year-old woman in whom MAS developed as a complication of ankylosing spondylitis (AS). She suffered from fever and low back pain before admission. Laboratory findings were pancytopenia, abnormal liver enzymes, increased ferritin levels, and positive for B27. Hyperplasia of hemophagocytic macrophages was confirmed in her bone marrow. High-dose steroids therapy resulted in clinical and laboratory improvements. In this patient, there was no possible causative factor of HPS (such as viral infection, lymphoma, and systemic lupus erythematosus) except the presence of AS. There have been no previously reported cases describing the relationship between AS and HPS. This case indicates that attention should be given to the possibility that certain patients with AS-associated cytopenia may display accompanying intramedullary hemophagocytic phenomena.