Felty's Syndrome.

Felty's syndrome is a complication of rheumatoid arthritis whereby patients develop neutropenia of varying severity. Although the main clinical concern is the development of serious infections, often patients remain asymptomatic or continue with clinical problems related to the rheumatoid arthritis and not to the neutropenia. There is now considerable clinical experience with the use of the recombinant human haemopoietic growth factors granulocyte and granulocyte-macrophage colony-stimulating factors (G-CSF and GM-CSF) in the treatment of patients with Felty's syndrome. The only indication for the use of either growth factor for Felty's syndrome is the onset of infectious complications, which may be recurrent and serious. In general, when this occurs, the neutropenia is severe (<10(8) cells/L). The mechanism(s) underlying development of the neutropenia in Felty's syndrome is similar to that in other forms of immune-mediated neutropenia, and in general is associated with a terminal defect in neutrophil maturation. It is likely that the maturational defect is a consequence of ;immune based' inhibition, although we lack detailed understanding of this inhibitory process. Growth factor therapy does not relieve the defect in terminal maturation, but in general may induce a significant improvement in the peripheral white cell count. Instances where growth factor therapy does not work appear to be due to an inability to overcome the maturational defect. Thus, the level of granulopoietic inhibition mediated by the rheumatoid process varies in severity among patients. To date, treatment options for Felty's syndrome have included disease-modifying antirheumatic drugs, corticosteroids and splenectomy. The addition of growth factor therapy is a welcome addition to these less than optimal treatment options. However, all of the above therapies fail on occasion. Moreover, the dosage and frequency of growth factors must be titrated to keep the white blood cell count <5 x 10(9) cells/L, since overshoot may result in complications, the most common being exacerbation of the rheumatoid arthritis. Another mechanism by which these drugs may exacerbate rheumatoid arthritis is through activation of neutrophils. The addition of disease-modifying drugs may relieve the maturational defect, improve the peripheral white cell count and minimise disease exacerbation by limiting neutrophil exposure to the administered haemopoietic growth factor. However, long term monotherapy with G-CSF has been successfully employed without requiring disease-modifying therapy.