Which of the following occurs in idiopathic myelofibrosis?

In idiopathic myelofibrosis, the hallmark feature is bone marrow fibrosis. This condition leads to the proliferation of collagen fibers within the bone marrow, which disrupts normal hematopoiesis (the production of blood cells). As a result, the bone marrow becomes less able to produce blood cells effectively, leading to a range of hematological abnormalities. The presence of fibrosis is a significant indicator of the disease and distinguishes it from other myeloproliferative disorders.

The other options describe processes or outcomes not typically associated with idiopathic myelofibrosis. For instance, increased red blood cell production is not characteristic of this disorder; rather, patients often experience anemia due to ineffective hematopoiesis. A high eosinophil count is also not a typical feature of myelofibrosis, as this condition primarily affects myeloid cell lines. Normal erythropoiesis suggests a typical functioning bone marrow, which is contrary to the pathophysiology of myelofibrosis that is characterized by abnormal bone marrow architecture and function.