Myeloma may be called by several names, including plasma cell dyscrasia, plasma cell myeloma, myelomatosis and multiple myeloma. The disease may be referred to as Kahler’s disease, especially in Europe, in recognition of the physician who first published the most comprehensive description of myeloma.
The earliest observations of myeloma in patients were made by physicians in England in the mid-19th century. By the turn of the 20th century, physicians had described the essential features of the disease: its appearance as malignant plasma cells, its involvement in multiple sites in marrow, its destruction of bone and its association with abnormal proteins in the urine and later the blood. In the late 19th century, the term “myeloma” was used to indicate the disease, which is derived from the Greek word “myel-” meaning “marrow” and “-oma” meaning a “tumor”.
The major forms of myeloma are divided into categories. Myeloma involving multiple sites is by far the most common way in which the disease appears. Most cases (about 90 percent) have multiple sites involved at the time of diagnosis, and the term “multiple” is often applied. In cases that appear to have a different distribution, various other terms are used to describe the disease. These include: solitary myeloma (one site evident), localized myeloma (a few neighboring sites evident) or extramedullary myeloma (involvement of tissues other than the marrow, such as skin, muscle or lung). These categories allow the physician to decide what treatment works best for the particular type of disease. Myeloma results from an acquired (not inherited) injury to the DNA of a single cell in the lymphocyte development sequence that is destined to form plasma cells. Myeloma occurs in lymphocytes developing into B cells, as opposed to T cell development. B lymphocytes transform into plasma cells, which produce proteins called antibodies (see Figure 1).
Figure 1. The malignant transformation in myeloma may occur in the more developed B lymphocyte. In most cases, the affected lymphocytes can still complete step three and mature into plasma cells, which are different in appearance from lymphocytes. The early events of lymphocyte development take place principally in the lymph node. The lymphocyte then migrates to the marrow (another major site of plasma cell development and function), where further development occurs.
In the development of myeloma, a cell in the B lymphocyte development pathway transforms, or becomes malignant. The cells resulting from the malignant transformation are abnormal plasma cells, or myeloma cells. They sometimes look like normal plasma cells under the microscope. They may also have structural abnormalities that suggest they are malignant (cancer) cells.