Chronic lymphocytic leukemia | diagnosis

Diagnosis

Micrograph of a lymph node affected by B-CLL showing a characteristic proliferation center (right of image), composed of larger, lighter-staining, cells, H&E stain

CLL is usually first suspected by a diagnosis of lymphocytosis, an increase in a type of white blood cell, on a complete blood count test. This frequently is an incidental finding on a routine physician visit. Most often the lymphocyte count is greater than 5000 cells per microliter (µl) of blood, but can be much higher.[11] The presence of lymphocytosis in an elderly individual should raise strong suspicion for CLL, and a confirmatory diagnostic test, in particular flow cytometry, should be performed unless clinically unnecessary.

A peripheral blood smear showing an abundance of damaged cells known as "smudge cells" or "basket cells" can also indicate the presence of the disease (smudge cells are due to cancer cells lacking in vimentin, a cytoskeletal protein).[21]:1899

The diagnosis of CLL is based on the demonstration of an abnormal population of B lymphocytes in the blood, bone marrow, or tissues that display an unusual but characteristic pattern of molecules on the cell surface. This atypical molecular pattern includes the coexpression of cell surface markers clusters of differentiation 5 (CD5) and 23. In addition, all the CLL cells within one individual are clonal, that is, genetically identical. In practice, this is inferred by the detection of only one of the mutually exclusive antibody light chains, kappa or lambda, on the entire population of the abnormal B cells. Normal B lymphocytes consist of a stew of different antibody-producing cells, resulting in a mixture of both kappa- and lambda-expressing cells. The lack of the normal distribution of these B cells is one basis for demonstrating clonality, the key element for establishing a diagnosis of any B cell malignancy (B cell non-Hodgkin lymphoma).

The combination of the microscopic examination of the peripheral blood and analysis of the lymphocytes by flow cytometry to confirm clonality and marker molecule expression is needed to establish the diagnosis of CLL. Both are easily accomplished on a small amount of blood. A flow cytometer instrument can examine the expression of molecules on individual cells in fluids. This requires the use of specific antibodies to marker molecules with fluorescent tags recognized by the instrument. In CLL, the lymphocytes are genetically clonal, of the B cell lineage (expressing marker molecules clusters of differentiation 19 and 20), and characteristically express the marker molecules CD5 and CD23. These B cells resemble normal lymphocytes under the microscope, although slightly smaller, and are fragile when smeared onto a glass slide, giving rise to many broken cells, which are called "smudge" or "smear" cells.[22]

Smudge cells in peripheral blood

The Matutes's CLL score allows the identification of a homogeneous subgroup of classical CLL, that differs from atypical/mixed CLL for the five markers' expression (CD5, CD23, FMC7, CD22, and immunoglobulin light chain) Matutes's CLL scoring system is very helpful for the differential diagnosis between classical CLL and the other B cell chronic lymphoproliferative disorders, but not for the immunological distinction between mixed/atypical CLL and mantle cell lymphoma (MCL malignant B cells).[23] Discrimination between CLL and MCL can be improved by adding non-routine markers such as CD54[24] and CD200.[25] Among routine markers, the most discriminating feature is the CD20/CD23 mean fluorescence intensity ratio. In contrast, FMC7 expression can surprisingly be misleading for borderline cases.[26]

Clinical staging

Staging, determining the extent of the disease, is done with the Rai staging system or the Binet classification (see details[27]) and is based primarily on the presence of a low platelet or red cell count. Early-stage disease does not need to be treated. CLL and SLL are considered the same underlying disease, just with different appearances.[28]:1441

Rai staging system[29][30]

  • Stage 0: characterized by absolute lymphocytosis (>15,000/mm3) without lymphadenopathy, hepatosplenomegaly, anemia, or thrombocytopenia
  • Stage I: characterized by absolute lymphocytosis with lymphadenopathy without hepatosplenomegaly, anemia, or thrombocytopenia
  • Stage II: characterized by absolute lymphocytosis with either hepatomegaly or splenomegaly with or without lymphadenopathy
  • Stage III: characterized by absolute lymphocytosis and anemia (hemoglobin <11 g/dL) with or without lymphadenopathy, hepatomegaly, or splenomegaly
  • Stage IV: characterized by absolute lymphocytosis and thrombocytopenia (<100,000/mm3) with or without lymphadenopathy, hepatomegaly, splenomegaly, or anemia

Binet classification[31]

  • Clinical stage A: characterized by no anemia or thrombocytopenia and fewer than three areas of lymphoid involvement (Rai stages 0, I, and II)
  • Clinical stage B: characterized by no anemia or thrombocytopenia with three or more areas of lymphoid involvement (Rai stages I and II)
  • Clinical stage C: characterized by anemia and/or thrombocytopenia regardless of the number of areas of lymphoid enlargement (Rai stages III and IV)

Array-based karyotyping

Array-based karyotyping is a cost-effective alternative to FISH for detecting chromosomal abnormalities in CLL. Several clinical validation studies have shown >95% concordance with the standard CLL FISH panel.[32][33][34][35][36]

Related diseases

In the past, cases with similar microscopic appearance in the blood but with a T cell phenotype were referred to as T-cell CLL. However, these are now recognized as a separate disease group and are currently classified as T-cell prolymphocytic leukemias.[37][38]

CLL should not be confused with acute lymphoblastic leukemia, a highly aggressive leukemia most commonly diagnosed in children, and highly treatable in the pediatric setting.

Differential diagnosis

Lymphoid disorders that can present as chronic leukemia and can be confused with typical B-cell chronic lymphoid leukemia[39]
Follicular lymphoma
Splenic marginal zone lymphoma
Nodal marginal zone B cell lymphoma
Mantle cell lymphoma
Hairy cell leukemia
Prolymphocytic leukemia (B cell or T cell)
Lymphoplasmacytic lymphoma
Sézary syndrome
Smoldering adult T cell leukemia/lymphoma

Hematologic disorders that may resemble CLL in their clinical presentation, behavior, and microscopic appearance include mantle cell lymphoma, marginal zone lymphoma, B cell prolymphocytic leukemia, and lymphoplasmacytic lymphoma.

  • B cell prolymphocytic leukemia, a related, but more aggressive disorder, has cells with similar phenotype, but are significantly larger than normal lymphocytes and have a prominent nucleolus. The distinction is important as the prognosis and therapy differ from CLL.
  • Hairy cell leukemia is also a neoplasm of B lymphocytes, but the neoplastic cells have a distinct morphology under the microscope (hairy cell leukemia cells have delicate, hair-like projections on their surfaces) and unique marker molecule expression.

All the B cell malignancies of the blood and bone marrow can be differentiated from one another by the combination of cellular microscopic morphology, marker molecule expression, and specific tumor-associated gene defects. This is best accomplished by evaluation of the patient's blood, bone marrow, and occasionally lymph node cells by a pathologist with specific training in blood disorders. A flow cytometer is necessary for cell marker analysis, and the detection of genetic problems in the cells may require visualizing the DNA changes with fluorescent probes by FISH.