Myelodysplasia is classified into five categories according to its degree of hyperplasia: extremely active, markedly active, active, diminished, and extremely diminished. Normal human bone marrow images fall into the third category. This myeloproliferative disorder is a general term for a series of diseases caused by a continuous abnormal proliferation process of one or more lineages of bone marrow cells. Clinically, it is characterized by abnormalities in the number and shape of one or more blood cells, splenomegaly with a tendency to bleed, and the formation of blood clots.