Histological Features
In CLL, the abnormal lymphocytes have specific histological characteristics. Under a microscope, they appear as small, round cells with scant cytoplasm and dense, clumped chromatin. One of the hallmark features is the presence of
"smudge cells" (also called basket cells), which are fragile cells that rupture during slide preparation. These cells are typically seen in peripheral blood smears.
Bone Marrow Biopsy Findings
A bone marrow biopsy in CLL usually shows a hypercellular marrow with a predominance of small, mature lymphocytes. The infiltrating lymphocytes often form nodular or diffuse patterns. The marrow architecture can be disrupted, leading to a decreased production of normal blood cells.Immunophenotyping
Immunophenotyping is crucial for diagnosing CLL. Flow cytometry is used to analyze the expression of surface markers. CLL cells typically express
CD5, CD19, CD20, CD23, and low levels of surface immunoglobulins (sIg). The co-expression of CD5 and CD23 is particularly characteristic of CLL.
Cytogenetic and Molecular Features
Certain cytogenetic abnormalities are common in CLL, such as deletions in chromosomes 13q, 11q, and 17p, and trisomy 12. These genetic changes can influence the prognosis and response to treatment. For instance, the deletion of 17p, which involves the
TP53 gene, is associated with a poorer prognosis.
Role of Histology in Treatment Monitoring
Histological analysis is not only essential for diagnosing CLL but also for monitoring treatment response. Post-treatment bone marrow biopsies can help assess the extent of residual disease and guide further therapeutic decisions. A decrease in the number of malignant lymphocytes and restoration of normal marrow architecture are indicative of a positive response to treatment.Histological Differential Diagnosis
Several other conditions can mimic the histological appearance of CLL, necessitating a careful differential diagnosis. These include
Mantle Cell Lymphoma,
Follicular Lymphoma, and
Prolymphocytic Leukemia. Immunophenotyping and genetic studies are often required to distinguish between these entities.
Conclusion
Histology plays a pivotal role in the diagnosis, classification, and management of Chronic Lymphocytic Leukemia. Understanding the histological and immunophenotypic features of CLL is essential for accurate diagnosis and effective treatment planning.
