Laboratory Studies
CBC and differential
CBC is the most useful initial laboratory test in patients suspected of having leukemia. Most patients will show some abnormality in the CBC and some blasts will be seen in the peripheral smear in patients with acute leukemias.
To diagnose CLL, a lymphocytosis of greater than 5000/mm3 must be present. The absolute neutrophil count usually is normal (see the Absolute Neutrophil Count calculator) and red blood cell counts and platelet counts are mildly decreased. In addition, the peripheral smear or bone marrow should show normal mature small lymphocytes with less than 55% atypical or blast forms.
CML is defined by its peripheral WBC count. Typically, leukocytosis is in excess of 100,000/mm3. The differential count shows that neutrophil precursors are present. This is accompanied by basophilia and eosinophilia. Unlike those in AML, these cells are mature and functional.
Bone marrow aspiration
Bone marrow aspiration establishes the diagnosis of leukemia. The morphology of blasts usually can differentiate between ALL and AML.
In ALL, a homogeneous infiltrate of lymphoblasts replaces the normal bone marrow elements. Lymphoblasts usually are small and measure approximately 14 µm in diameter. They have scant cytoplasm with no granules. The nucleus has no nucleoli or a small indistinct one.
For the diagnosis of AML, 30% of the nucleated cells in the aspirate must be blast cells of myeloid origin. Multiple large nucleoli, delicate chromatin, gray-blue cytoplasm, and Auer rods characterize myeloblasts. The presence of Auer rods is virtually diagnostic of AML, because these condensed lysosomal cytoplasmic azurophilic rod-shaped structures do not appear in ALL.
In CLL, bone marrow infiltration exceeds 30% lymphocytes. The lymphocytes are mature with less than 55% atypical or blast forms. The nuclei are round, cytoplasm is scant, chromatin is compact, nucleoli are inconspicuous, and mitotic figures are rare.
Immunophenotyping
Immunophenotyping using multiparameter flow cytometry following labeling with monoclonal antibodies to cell-surface antigens identifies the B or T cell origin of the lymphoblasts.
Based on the expression of B lineage-restricted antigens and clonal rearrangements of immunoglobulin heavy and light chain genes, it has been estimated that up to 80% of ALL cases arise from B-cell precursors. The majority possesses a common ALL antigen (CALLA) that is present only on leukemic cells.
T-cell ALL possesses receptors for sheep erythrocytes, and, when these are combined, they form E-rosettes.
A final subset of ALL lacks B- or T-cell characteristics and is referred to as null-cell ALL.
Certain myeloid-specific antigens, such as CD13, CD33, and CD41, have been used to diagnose AML.
The malignant cells in CLL correspond to a minor subpopulation of B cells that express cell surface immunoglobulin M (IgM) and immunoglobulin D (IgD) and the T-cell associated antigen CD5.
Histochemical stains
Histochemical stains for myeloperoxidase (Leder stain) and nonspecific esterase have a strong affinity for myelogenous precursors but fail to stain lymphocytic forerunners.
Demonstration of nuclear DNA polymerizing enzyme terminal deoxynucleotidyl transferase (TdT) is indicative of a lymphoid origin. However, up to 2-5% of patients with AML exhibit this enzyme. Exceptions may occur when a malignant clone arises from multipotent cells that may express both myelogenous characteristics and lymphocytic characteristics.
Chromosomal analysis
Chromosomal analysis also plays an important role. The diagnosis of CML is established by identifying cytogenetically or molecularly a clonal expansion of a hematopoietic stem cell possessing a reciprocal translocation between chromosomes 9 and 22.
Chromosomal analysis of the leukemic cell currently provides the most important pretreatment prognostic information in AML.
Imaging Studies
Fluorescein angiography may reveal myriad diffuse leakage points at the level of the RPE. This pattern also may be seen in Vogt-Koyanagi-Harada disease, diffuse choroidal melanoma, metastatic tumors, and posterior scleritis.
Optical coherence tomography (OCT) can help confirm the diagnosis of macular exudative detachment. OCT can also be useful in monitoring patients following treatment.
Histologic Findings
Histopathologic studies have shown the choroid to be the ocular structure most commonly involved by leukemia. The choroid is thickened, especially at the posterior pole. The RPE may be hyperplastic, atrophied, or hypertrophied. Photoreceptor loss, drusen formation, serous detachment, and cystoid retinal edema may be present.
Immature white blood cells infiltrate the retina, and, when they accumulate, nodular masses may be seen. The retinal vessels usually are packed with immature leukocytes. Capillary nonperfusion may result due to massive accumulation of cells. Diffuse infiltration of the iris and the ciliary body is commonly seen. The infiltrates are usually denser near the sphincter and the base of the iris. The trabecular meshwork may be clogged with leukemic cells leading to glaucoma.
Histopathologic studies indicate that leukemic infiltration in the orbit most often was mild and diffuse as opposed to massive and tumorous. A chloroma of the orbit is composed of immature granulocyte cells, which contain large amounts of the enzyme myeloperoxidase, giving the tumor a greenish hue on gross examination. Because of the poorly differentiated nature of this tumor on histological examination and often unremarkable CBC, it may be misdiagnosed as a lymphoma.
Histologic diagnosis of lymphoma in a rapidly growing orbital mass of a child is unlikely because orbital lymphomas in children are quite rare.
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A 4-year-old boy presented with sudden proptosis of his left eye.
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Same patient as in the image above. A CBC revealed anemia (Hb 8.6 mg/dL), thrombocytopenia (64,000), and leukocytosis (12,900). The peripheral smear revealed the presence of blasts 28%, lymphocytes 44%, segmented 14%, monocytes 6%, bands 2%, metamyelocytes 1%, and myelocytes 1%. The boy was diagnosed with AML type M4-M5 chloroma of the left orbit.
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CT scan reveals infiltration in the left orbit. Notice that the bone is uninvolved. A lumbar puncture revealed that the cerebral spinal fluid was clean of leukemic cells.
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Systemic chemotherapy was instituted, and the proptosis resolved. Unfortunately, 4.5 months later, the boy passed away secondary to multiorgan failure.
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An impending bilateral central retinal vein obstruction was discovered during a routine examination of a 76-year-old man. Further workup revealed a WBC count of 709,000, a hemoglobin count of 12 mg/dL, and a platelet count of 104,000. The man was eventually diagnosed with CML. This image is a red-free photograph of the right fundus. Notice the intraretinal hemorrhages.
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Same patient as in the image above. This image is a red-free photograph of the left eye showing intraretinal hemorrhages.
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A 14-year-old boy with a past medical history of ALL complained of a sudden loss of vision OD. Visual acuities were counting fingers OD and 20/20 OS. Notice the macular hemorrhage responsible for the loss of vision. Courtesy of Dr Rafael Jiménez.
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Same patient as in the previous image. The hematological workup revealed a hemoglobin count of 5.6, a WBC count of 1800, and a platelet count of 3000. Courtesy of Dr Rafael Jiménez.
