Extramedullary Involvement

More uncommonly, patients present with symptoms secondary to leukemic infiltration of various tissues, leading to hepatomegaly, splenomegaly, leukemia cutis (2-10% of patients), gingival involvement, tumorous nodules (myeloid sarcoma) (3-5% of patients), lymphadenopathy, bone, or central nervous system (CNS) involvement (1% of patients).3'5 Occasionally, patients may present with pericardial effusions.2 Pulmonary infiltrates may also represent leukemia. Leukemic infiltrates in the lungs occur more commonly in patients presenting with high white blood counts and a monocytic component to their leukemia. Computed tomographic scan and bron-

choscopy may be needed to make a definitive diagnosis and to rule out other etiologies, such as infection and pulmonary hemorrhage.

Extramedullary involvement is more common with the monocytic or myelomonocytic subtypes of AML, and may be associated with a worse prognosis. The cytogenetic abnormality most commonly associated with extramedullary leukemia is t(8;21)(q22;q22).5,6 The incidence of extramedullary leukemia appears to be particularly high in patients who relapse, and may be decreasing with the use of intensive high-dose cytarabine as consolidation.5 The most common site of extramedullary leukemia in patients with the t(8;21)(q22;q22) abnormality is paraspinal disease.5 The presence of CD56, an adhesion molecule expressed in a variety of tissues including neural tissues, may be an additional risk factor for extramedullary leukemia in patients with t(8;21) or monocytic AML.5,7-9

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