Felty's syndrome is an autoimmune syndrome characterized by a combination of arthritic joints, an enlarged spleen and an abnormally low white blood cell count. It is generally a disease of the elderly, being far more likely to appear between the ages of 50 and 70. It is also more likely to appear in females and people of European ancestry. Unlike rheumatoid arthritis, Felty's is more likely to cause deformation at the joints in addition to pain. However, because the conditions are otherwise quite similar, many Felty's patients are misdiagnosed with the more common condition, making Felty's a zebra.
As a result, the treatment is quite different. Arthritis will usually respond to NSAIDs, but Felty's patients may need steroids or even chemotherapy to modulate their immune system and prevent complications.