Chronic Leukemias
Patients with a chronic leukemia typically present with much less severe illness than those with an acute leukemia. Chronic leukemia is usually diagnosed incidentally based on high white blood cell counts. The chronic leukemias are divided into two groups according to the cell of origin: chronic lymphocytic leukemia and chronic myelogenous leukemia.

Chronic lymphocytic leukemia results from the proliferation and persistence (lack of apoptosis) of relatively mature-appearing lymphocytes. The spleen and lymph nodes are enlarged because of the excessive accumulation of lymphocytes. Despite the increased number of lymphocytes, this disease is associated with impaired immunity as a result of the scarcity of normal lymphocytes.

In the absence of symptoms, such as fever, sweats, weight loss, anemia, moderate thrombo-cytopenia or organ enlargement, the leukocytosis usually does not require treatment.

Chronic myelogenous leukemia, which affects myeloid cells (polymorphonuclear cells and less mature cell forms), is frequently diagnosed after the incidental finding of a high white blood cell count.
Middle-aged adults more commonly develop chronic myelogenous leukemia. Some patients describe fatigue, bleeding or weight loss. Splenomegaly is frequently present, and the markedly enlarged spleen sometimes causes abdominal discomfort, indigestion or early satiety. Lymphadenopathy is uncommon.

Platelet counts are usually normal to increased. In fact, chronic myelogenous leukemia is the only leukemic process that is associated with thrombocytosis. Another laboratory feature that distinguishes this disease from other leukemias and myeloproliferative disorders is the presence of the Philadelphia chromosome, an abnormality of translocation between chromosome 22 and chromosome 9.

Chronic myelogenous leukemia eventually develops an accelerated phase and subsequently transforms into acute leukemia. The accelerated phase is characterized by fever, sweats, weight loss, bone pain, bruising and hepatosplenomegaly. During this time, thrombocytopenia and anemia develop. The median time for transformation of chronic myelogenous leukemia to acute leukemia is two to five years. After the development of acute leukemia, median survival is short.

Table 6 - Differential Characteristics of Acute and Chronic Leukemias
Patient group and type of leukemia	Symptoms	Signs	Laboratory findings
Children: acute lymphocytic leukemia	Infection,bleeding, weakness	Enlarged liver, spleen or lymphnodes	Variable white blood cell count, anemia, thrombocytopenia, blast cells
Adults: acute nonlymphocytic leukemia (acute myeloid leukemia)
Adults: chronic myelogenous leukemia	None, or malaise and abdominal discomfort	Enlarged spleen	Leukocytosis (myeloid precursors), normal or increased platelet count
Older adults: chronic lymphocytic leukemia	None, or nonspecific symptoms	Enlarged spleen or lymph nodes	Leukocytosis (lymphocytes)