Sandbox: leukemia
Pathophysiology
CLL affects a particular lymphocyte, the B cell, which originates in the bone marrow, develops in the lymph nodes, and normally fights infection. In CLL, the DNA of a B cell is damaged, so that it can't fight infection, but it grows out of control and crowds out the healthy blood cells that can fight infection.
CLL is an abnormal neoplastic proliferation of B cells. The cells accumulate mainly in the bone marrow and blood. CLL is closely related to a disease called small lymphocytic lymphoma (SLL), a type of non-Hodgkin's lymphoma which presents primarily in the lymph nodes. The World Health Organization considers CLL and SLL to be "one disease at different stages, not two separate entities".[1]
In the past, cases with similar microscopic appearance in the blood but with a T cell phenotype were referred to as T-cell CLL. However, it is now recognized that these so-called T-cell CLLs are in fact a separate disease group and are currently classified as T-cell prolymphocytic leukemias.
Acute lymphocytic leukemia (ALL) is a disease of children, but CLL is a disease of adults.
Uncommonly, CLL presents as enlargement of the lymph nodes without a high white blood cell count or no evidence of the disease in the blood. This is referred to as small lymphocytic lymphoma.
The increase in lymphocytes and precursors in the bone marrow impairs the production of other leucocytes causing a decrease in such cell types.