Myelofibrosis with myeloid metaplasia: pathophysiologic implications of the correlation between bone marrow changes and progression of splenomegaly

We undertook a study of 35 cases of myelofibrosis with myeloid metaplasia to assess the histopathologic findings in the bone marrow of patients with this disorder, to ascertain if changes in morphology occurred with time, and to attempt to correlate marrow findings with splenic size. We reviewed 71 bone marrow biopsies and studied 13 splenectomy specimens. Sequential bone marrow biopsies were obtained in 21 cases over intervals ranging from two to ten years (mean, 4 1/2 years). We noted a patchy nature and variable degree of stromal proliferation in most marrow biopsies, and were unable to demonstrate a correlation between the extent of medullary fibrosis and duration of disease, splenic weight, or degree of splenic myeloid metaplasia. We were unable to document a progression of medullary fibrosis as a cause for increasing splenomegaly. However, the alteration in the marrow stroma in this disorder is responsible for the presence of distended marrow sinusoids with intravascular hematopoiesis, a phenomenon we observed in all cases. We believe that this morphological feature, not emphasized by previous investigators, is of significance in understanding the pathophysiology of myeloid metaplasia.