Felty syndrome (FS) occurs in a small subset of patients with rheumatoid arthritis (RA) associated with neutropenia and splenomegaly. The cause of FS is unknown but it has been linked to positive rheumatoid factor (RF), anticyclic citrullinated peptide antibodies (anti-CCP), and human leukocyte androgen (HLA)-DR4. It is sometimes associated with a somatic mutation in the STAT3 gene. Approximately 1% of patients with RA will develop FS in their lifetime, and it usually occurs 10 years after the diagnosis of RA. FS is rare in children. There is a female predilection. FS usually occurs in individuals of Northern European descent; it is less common in individuals of African descent.

Clinical signs and symptoms include splenomegaly, rheumatoid nodules, joint deformities, synovitis, necrotizing skin lesions, mononeuritis multiplex, lymphadenopathy, episcleritis, neutropenia (absolute neutrophil count [ANC] < 2000), recurrent bacterial infections, and in some cases, portal hypertension. These patients also have an increased risk of non-Hodgkin lymphoma.

The treatment of FS centers on reversal of neutropenia to prevent severe infections. This is typically done with disease-modifying antirheumatic drugs (DMARDs). Splenectomy can be considered in patients who are refractory to medical therapy.