A rare myeloproliferative neoplasm characterized by stem-cell derived clonal over proliferation of mature myeloid lineages, such as erythrocytes, leukocytes, and megakaryocytes, with variable degrees of megakaryocyte atypia, associated with reticulin and/or collagen bone marrow fibrosis, osteosclerosis, ineffective erythropoiesis, angiogenesis, extramedullary hematopoiesis, and abnormal cytokine expression.

Difficulty in breathing. The physical presentation of respiratory distress is generally referred to as labored breathing, while the sensation of respiratory distress is called shortness of breath or dyspnea.