An atypical myeloproliferative disorder with high thrombotic risk and slow disease progression

The chronic myeloproliferative disorders (CMD) represent a group of diseases which have in common the abnormal proliferation of some cell contributing to the blood. All are thought to arise when a single cell in the bone marrow goes awry and multiplies without adherence to its original 'plan'. If the cell is a precursor of red blood cells, then polycythemia vera is the result. If the precursor cell is a megakaryocyte, which forms platelets (thrombocytes), then idiopathic thrombocythemia is the result. Other myeloproliferative syndromes include myelofibrosis with myeloid metaplasia and chronic myelogenous leukemia. While these classes represent many of the cases observed in the clinic, there are intermediate forms which share features of two typical classes. Furthermore, there seem to be variant forms which have features of chronic myeloproliferative disorders but are not immediately recognizable as such. The authors describe the important features of 18 cases that failed to satisfy the diagnostic criteria for the typical forms of CMD. All 18 cases occurred in patients younger than 46 years of age. In 11 cases, the patients had signs such as enlarged spleen, excessive bone marrow growth, and a mild increase of platelets or white blood cells in the blood. Rare immature bone marrow cells appeared in the blood of some of the 11 patients. In the other seven patients, a diagnosis of CMD was made only after an enlarged spleen was removed and blood clotting complications began. In two cases, these complications were fatal. Fifteen patients are alive and appear stable; in 12 chemotherapeutic treatment to kill the renegade cells has not proved necessary. These cases illustrate the features of a slowly progressing chronic myeloproliferative disorder affecting younger patients. They also illustrate the dangers of removing an enlarged spleen when the cause of the splenomegaly has not been determined. (Consumer Summary produced by Reliance Medical Information, Inc.)