Initial (prefibrotic) stages of idiopathic (primary) myelofibrosis (IMF) - a clinicopathological study

A clinicopathological follow-up study including sequential bone marrow biopsies was performed on 79 patients with idiopathic (primary) myelofibrosis (IMF) to characterize initial (prefibrotic) stages and to elucidate whether development of fibrosis was accompanied by corresponding clinical findings. For this purpose our cohort of patients was divided into two groups of which the first presented with the generally accepted signs and symptoms of IMF (group I; n = 60). Most patients of the second group (group II; n = 19) showed mild to moderate therapy-refractory anemia, minimal to slight splenomegaly and frequently thrombocytosis, but no bone marrow fibrosis at onset. Hematopoiesis was consistent with a striking hypercellularity in comparison to the age-related involution by adipose tissue, a conspicuous clustering and histotopographic dislocation of megakaryocytes, a neutrophil granulocytic proliferation and a reduction of erythropoietic islets with arrest of maturation. Most remarkable was the dysplastic cytology of megakaryocytes with a definitive deviation of differentiation resulting in bizarre forms. Follow-up examinations revealed that at later stages group II patients were not distinguishable from the first group with more advanced IMF. For this reason, these patients were regarded as presenting initial, prefibrotic IMF characterized by distinctive bone marrow features at the beginning. The prominent abnormalities of megakaryopoiesis together with the granulocytic proliferation were extremely helpful to differentiate prefibrotic IMF with accompanying thrombocythemia from essential thrombocythemia (ET). Dynamics of fiber progression were calculated by regarding increase in density per time. Speed of progression during the first year of observation proved to be significantly higher in group II patients with prefibrotic IMF in comparison to full-blown cases (group I). In conclusion, with respect to prospective clinical trials, diagnostic criteria for IMF should be re-evaluated by also taking initial, prefibrotic stages into account.