REACTIVE CHANGES IN WHITE BLOOD CELLS
Leukocytosis is characterized by an elevated white blood cell count. It has the fol-lowing features:
• Increased neutrophils (neutrophilia)
Increased bone marrow production is seen with acute inflammation associated with pyogenic bacterial infection or tissue necrosis
Increased release from bone marrow storage pool may be caused by corti costeroids, stress, or endotoxin
Increased bands (“left shift”) noted in peripheral circulation
Reactive changes include Döhle bodies (aggregates of rough endoplasmic reticulum), toxic granulations (prominent granules), and cytoplasmic vacuoles of neutrophils
• Increased eosinophils (eosinophilia) occurs with allergies and asthma (type I hypersensitivity reaction), parasites, drugs (especially in hospitals), and certain skin diseases and cancers (adenocarcinomas, Hodgkin disease).
• Increased monocytes (monocytosis) occurs with certain chronic diseases such as some collagen vascular diseases and inflammatory bowel disease, and with certain infections, especially TB.
• Increased lymphocytes (lymphocytosis) occurs with acute (viral) diseases and chronic inflammatory processes.
Infectious mononucleosis, an acute, self-limited disease, which usually resolves in 4–6 weeks, is an example of a viral disease that causes lymphocytosis. The most common cause is Epstein-Barr virus (a herpesvirus) though other viruses can cause it as well (heterophile-negative infectious mononucleosis is most likely due to cytomegalovirus).
Age groups include adolescents and young adults (“kissing disease”).
The “classic triad” includes fever, sore throat with gray-white membrane on tonsils, and lymphadenitis involving the posterior auricular nodes. Another sign is hepatosplenomegaly.
Complications include hepatic dysfunction, splenic rupture, and rash if treated with ampicillin.
Diagnosis is often made based on symptoms. Lymphocytosis and a rising titer of EBV antibodies are suggestive of the infection. Atypical lymphocytes may be present in peripheral blood. Mono-spot test is often negative early in infection.
• Increased basophils are seen with chronic myeloproliferative disorders such as polycythemia vera.
Leukopenia is characterized by a decreased white blood cell count. It has the fol-lowing features:
• Decreased neutrophils can be due to decreased production (aplastic anemia, chemotherapy), increased destruction (infections, autoimmune disease such as systemic lupus erythematosus), and activation of neutrophil adhesion mol-ecules on endothelium (as by endotoxins in septic shock).
• Decreased eosinophils are seen with increased cortisol, which causes seques-tering of eosinophils in lymph nodes; examples include Cushing syndrome and exogenous corticosteroids.
• Decreased lymphocytes are seen with immunodeficiency syndromes such as HIV, DiGeorge syndrome (T-cell deficiency), and severe combined immu-nodeficiency (B- and T-cell deficiency); also seen secondary to immune destruction (systemic lupus erythematosus), corticosteroids, and radiation (lymphocytes are the most sensitive cells to radiation).
Lymphadenopathy is lymph node enlargement due to reactive conditions or neo-plasia.
Acute nonspecific lymphadenitis produces tender enlargement of lymph nodes; focal involvement is seen with bacterial lymphadenitis. Microscopi-cally, there may be neutrophils within the lymph node. Cat scratch fever (due to Bartonella henselae) causes stellate microabscesses. Generalized involve-ment of lymph nodes is seen with viral infections.
Chronic nonspecific lymphadenitis causes nontender enlargement of lymph nodes. Follicular hyperplasia involves B lymphocytes and may be seen with rheumatoid arthritis, toxoplasmosis, and early HIV infections. Paracortical lymphoid hyperplasia involves T cells and may be seen with viruses, drugs (Dilantin), and systemic lupus erythematosus. Sinus histiocytosis involves macrophages and, in most cases, is nonspecific; an example is lymph nodes draining cancers.
Neoplasia usually causes nontender enlargement of lymph nodes. The most common tumor to involve lymph nodes is metastatic cancer (e.g., breast, lung, malignant melanoma, stomach and colon carcinoma), which is initially seen under the lymph node capsule. Other important causes of lymphadenopathy are malignant lymphoma and infiltration by leukemias.