Prefibrotic chronic idiopathic myelofibrosis--a diagnostic enigma?

To analyze precursor lesions of chronic idiopathic myelofibrosis (CIMF) 21 patients were recruited who developed manifest myelofibrosis after about 70 months, preceded by a prefibrotic stage but without interference by cytoreductive therapy. Prodromal bone marrow lesions included a prominent granulocytic and megakaryocytic proliferation with megakaryocytes showing conspicuous abnormalities associated with a borderline to slight anemia, thrombocytosis, and minimal splenomegaly. Comparison of this cohort with 211 additional patients at this precursor stage revealed no differences concerning clinical findings and bone marrow histopathology. Relative incidence of prefibrotic CIMF was 24% and median survival 143 months, thus contrasting overt CIMF (82 months). In CIMF progressive myelofibrosis occurred in more than 50% of patients according to the last biopsy specimen; however, this figure increased according to relevant clinical data in the follow-up period.