Lymphocytosis Lymphocytes normally represent 20 to 40 percent of circulating white blood cells. Hence, the occurrence of lymphocytosis often translates into an increase in the overall white blood cell count. Increased numbers of lymphocytes occur with certain acute and chronic infections (Table 4). Malignancies of the lymphoid system may also cause lymphocytosis.
Relative, rather than absolute, leukocytosis occurs in a number of clinical situations, such as infancy, viral infections, connective tissue diseases, thyrotoxicosis and Addison’s disease. Splenomegaly causes relative lymphocytosis as a result of splenic sequestration of granulocytes.
| Table 4 - Etiology of Lymphocytosis |
Absolute lymphocytosis
Acute infections: cytomegalovirus infection, Epstein-Barr virus infection, pertussis, hepatitis, toxoplasmosis
Chronic infections: tuberculosis, brucellosis
Lymphoid malignancies: chronic lymphocytic leukemia
Relative lymphocytosis
Normal in children less than 2 years of age
Acute phase of several viral illnesses
Connective tissue diseases
Thyrotoxicosis
Addison’s disease
Splenomegaly with splenic sequestration |
| Table 5 - Clinical Factors Increasing Suspicion of an Underlying Bone Marrow Disorder |
Leukocytosis: white blood cell count greater than 30,000 per mm3 (30 X 109 per L)*
Concurrent anemia or thrombocytopenia. Organ enlargement: liver, spleen or lymph nodes.
Life-threatening infection or immunosuppression.
Bleeding, bruising or petechiae Lethargy or significant weight loss |
Leukocytosis with Primary Bone Marrow Disorders
Clinical factors that increase suspicion of an underlying bone marrow disorder are listed in Table 5. Bone marrow disorders are generally grouped into leukemias and myeloproliferative disorders.
Marrow abnormalities may occur with stem cells (acute leukemia) or more differentiated cells (chronic leukemia). Delineating acute leukemias from chronic leukemias is clinically important because the acute forms are more often associated with rapidly life-threatening complications such as bleeding, brain infarction and infection. Differences in the clinical presentations of acute and chronic leukemias are provided in Table 6.
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