Felty's syndrome: favorable response to granulocyte-macrophage colony-stimulating factor in the acute phase.

We report a case of Felty's syndrome in which infectious complications due to severe neutropenia could be overcome by short-term treatment with recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF, 7 micrograms/kg/day s.c.). Leukocyte counts rose from 1,050/mm3 at presentation to 4,470/mm3 after 15 days of treatment. A flare-up of arthritis was not noted. Defects in granulocyte function and clinical improvement prior to leukocyte rise suggest that the beneficial effect of GM-CSF is mainly due to an improvement of granulocyte function.