Diagnosing leukemia

A tentative diagnosis of leukemia is made after a physical examination of the child and
microscopic analysis of a blood sample have been conducted. Physical findings may
include pale skin; bruising or unusual bleeding; enlarged liver, spleen, or lymph nodes;
weakness; and fever (with or without a specific site of infection). Parents or children
may describe irritability, night sweats, fatigue, bone pain, and loss of appetite. Blood
tests may show decreased red cells, decreased platelets, and either abnormally low or
high white blood cell counts. There may be blast cells circulating in the blood.
The T-cell type of acute lymphoblastic leukemia (ALL) sometimes involves the
thymus gland in the neck. Enlargement of the thymus can pressure the nearby trachea
(windpipe), causing coughing or shortness of breath. The superior vena cava (SVC),
a large vein that carries blood from the head and arms back to the heart, passes next
to the thymus. An enlarged thymus gland may compress the SVC and cause swelling
of the head and arms. Some children with leukemia have the disease in their central
nervous system (brain and spinal cord) at diagnosis. Less than 10 percent of children
with leukemia have symptoms of CNS disease, including headache, poor school
performance, weakness, seizures, vomiting, blurred vision, and difficulty in main-
taining balance.
Children with acute myeloid leukemia (AML) are sometimes diagnosed after develop-
ing a chloroma—a tumor arising from myeloid tissue and containing myeloperoxi-
dase (a pale green pigment). These are most often found under the skin near the eyes
but may occur at any site in the body.
To confirm a diagnosis of leukemia, bone marrow is sampled and tested (see Chap-
ter 3, Coping with Procedures). The bone marrow is examined under a microscope by a
pediatric oncologist and/or a pathologist (a physician who specializes in body tissue
analysis). The diagnosis of leukemia is confirmed if more than 25 percent of the
blood cells in the marrow are blasts. A portion of the bone marrow (and chloroma
biopsy if done) is sent to a specialized laboratory that analyzes many other features of
the leukemic cells (chromosomes, proteins on the cell surface, and others).