Some people with rheumatoid arthritis (RA) get a rare disorder known as Felty's syndrome (FS). It causes an enlarged spleen and a very low white blood count. It can be painful and lead to serious infections in some cases.
Less than 3% of people with RA develop FS, but those in their 50s, 60s, and 70s who've had RA for 10 years or longer are more likely to have it. It's also three times more common in women than men. Children rarely get FS.