Like acute leukemia, there are two major categories based on cell appearance, histo-chemical stains and biological markers. Because chronic leukemias involve cells that are either mature or become mature, these cells may have a normal appearance.
The two major types of chronic leukemia are chronic myelogenous leukemia (CML) and chronic lymphocytic leukemia (CLL). They are easily distinguished under the microscope.
• CLL involves mature lymphocytes , cells that differ from the cells in CML in size, nuclear pattern and
generally by the absence of cellular particles. The diagnosis of CLL can be confirmed by cell surface marker
studies. These studies can be particularly helpful because sometimes appearance alone may not distinguish
between CLL and lymphoma that happen to involve the blood and/ or bone marrow .
• The CML cells are larger and appear normal. Chromosome studies on CML cells are sometimes needed to tell
the difference between a person with CML and preleukemia (myelodysplastic syndrome) or even someone
with a normal elevation in peripheral blood counts because of an infection. The more sensitive DNA analysis
of the CML cells may be used to confirm a diagnosis. In 80 to 90 percent of CML patients, the chromosomal
and DNA abnormality will confirm the presence of the (abnormal) Philadelphia chromosome.
Most people with CML and CLL have a high white blood cell count but may have few or no symptoms. A good number of these cases are diagnosed on a routine blood test performed as part of a routine or pre-employment physical examination. A doctor may find an enlarged spleen in someone with CML, and enlarged lymph nodes , with or without an enlarged spleen, in those with CLL.
