Ferrokinetic study of splenic erythropoiesis: relationships among clinical diagnosis, myelofibrosis, splenomegaly, and extramedullary erythropoiesis.

Splenic erythropoiesis was demonstrated by surface counting of 59Fe in 129 of 1,350 ferrokinetic studies performed over a 15 year period. These 129 studies were carried out in 108 patients, including 40 with chronic myelogenous leukemia (CML), 24 with agnogenic myeloid metaplasia (AMM), 18 with polycythemia vera (PV), six with a myelodysplastic syndrome, five with acute leukemia, three with prostate or breast carcinoma, two each with aplastic anemia or Hodgkin's disease, and one each with idiopathic thrombocythemia, multiple myeloma, chronic renal failure, or treated hypopituitarism. Splenomegaly was present in 83% of the studies and hepatomegaly in 72%. Grade II-III myelofibrosis was demonstrated in 62% of the cases. Hepatic erythropoiesis was present in 77% of the studies (only 38% in PV), and marrow erythropoiesis was undetectable in 33%. Total erythropoiesis was about twice normal (range 0.2 to 8 times normal) but was ineffective to varying degrees in 86% of the studies. Relationships between organomegaly, myelofibrosis, and extramedullary erythropoiesis, as well as differences among clinical disorders, are discussed. Differences observed between CML in chronic or blastic phase suggested that the erythroid cell line was involved in the proliferative process. It is concluded that splenic erythropoiesis 1) is encountered in a variety of clinical conditions; 2) is not necessarily associated with splenomegaly or myelofibrosis, even in the myeloproliferative disorders; 3) is part of a predominantly extramedullary (in the liver as well as in the spleen), expanded, and largely inefficient total erythropoiesis; and 4) can be evaluated in a semiquantitative manner by surface counting.