context: 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. Doctors aren't sure what causes FS. Your white blood cells may have stopped fighting infections like they should. Or your bone marrow could be making abnormal white blood cells. Another theory is that your immune system attacks your white blood cells by mistake. FS doesn't always run in families, but some genes that raise your chances of getting it could be passed down to you. Signs of FS are similar to those of rheumatoid arthritis. They also overlap other autoimmune diseases -- a disease in which your immune system attacks your own healthy cells -- like lupus. Because of that, FS can be hard to diagnose. You may have: Anemia (not enough healthy red blood cells to move oxygen through your body) Burning eyes or discharge from them Fatigue Fever Loss of appetite or weight loss Pale skin Repeat infections or infections that take a long time to clear up, especially in your lungs, urinary tract, or blood Sores or brown spots on your legs Stiff, swollen, or painful joints, usually in your hands, feet, or arms You also will have a swollen spleen -- a fist-sized organ behind your left ribs. It controls the amount of white blood cells in your body and plays a key part in your immune system. If your spleen is bigger than normal, you may feel pain behind your left rib cage. You also may feel full soon after you eat because it's pressing against your stomach. Other times, an enlarged spleen doesn't cause any symptoms. If your doctor thinks you might have FS, he'll feel around your stomach to see if your spleen is enlarged. An imaging test may be needed to confirm it: MRI (magnetic resonance imaging): Powerful magnets and radio waves are used to make detailed images. CT scan (computerized tomography): Several X-rays taken from different angles are put together to show a more complete picture. Your doctor will also have you take a blood test. People with FS have very low levels of special white blood cells called neutrophils. These are important for fighting off bacterial infections. If your RA is under control, you may not need treatment for FS. If you do need help with your symptoms, there are ways to manage them: Drugs that slow down the disease: low-dose methotrexate ( Rheumatrex, Otrexup, Trexall) is often used to stop your FS from getting worse. It can cause some side effects, such as nausea and mouth ulcers. You'll also need regular tests to make sure MTX isn't hurting your liver. Other drugs your doctor might advise you to take include glucocorticoids or disease-modifying antirheumatic drugs ( DMARDs) that are used to treat RA, such as abatacept ( Orencia) and leflunomide ( Arava ). Drugs that affect your immune system: Rituximab ( Rituxan) is also a preferred treatment for FS and can shut off the part of your immune system that isn't working as it should. They're given by IV but may take up to a few weeks to work. Drugs that stimulate your white blood cells: Granulocyte colony-stimulating factor ( G- CSF) can help increase the number of white blood cells and help fight infection. Home care: Your doctor will tell you how much physical activity and rest you need. A heating pad may help with mild aches and pains. A nonsteroidal anti-inflammatory drug ( NSAID) such as ibuprofen can also help. Surgery: If your FS is severe and other treatments don't work, your doctor may recommend that your spleen be taken out. This could return your red and white blood cells to normal levels and may lower your risk of infection for an indefinite amount of time.