Page 2609 - Hematology_ Basic Principles and Practice ( PDFDrive )

2322 Part XIII Consultative Hematology

Distensible splenic tissues results in pooling of a large amount of Reticuloendothelial blockade, or occupancy of these receptors, refers
blood, whereas the venous drainage is occluded by sickled hypoxic to the impaired ability of the spleen to recognize and remove other
erythrocytes. Patients with sickle cell disease who have not yet had IgG-coated particles, including bacteria, in the presence of these
multiple episodes of infarction and whose spleens have not undergone agents.
fibrosis are susceptible to this syndrome. Unlike the chronic process
of smaller vessel infarction, the acute splenic sequestration crisis can
be life threatening because a large amount of blood can collect in the SPLENOMEGALY AND HYPERSPLENISM
highly distended spleen. The tendency for recurrence and the poten-
tial for fatal outcome have resulted in the common recommendation An enlarged spleen is not a disease state in itself but usually indicates
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for splenectomy in a patient who has had one severe splenic sequestra- some underlying pathologic state. The processes run the gamut
tion crisis, or more than one less severe crisis. Occlusion of venous from minor to life threatening, from congenital disorders to those at
drainage also occurs in the liver, but the less distensible capsule of the the end of life. It is useful to approach the differential diagnosis of
liver and the options for venous drainage through the portal system splenomegaly by considering the processes that may cause splenic
make this less likely to be life threatening. enlargement and then to focus on the specific diagnoses within those
categories. The spleen may be enlarged as a result of infiltration,
hypertrophy of normal elements (macrophages and lymphoid com-
Immunologic and Autoimmune Diseases ponents), extramedullary hematopoiesis, inflammatory or immuno-
logic processes, and systemic or portal congestion (see box on Timing
Poor phagocytic function of the spleen is associated with impaired of Return to Contact Sports in Athletes Who Have Had Infectious
function of the Fc receptors on splenic macrophages in a variety of Mononucleosis). The degree of splenomegaly correlates well with
immunologic, rheumatic, and inflammatory disorders. Among those involvement of the spleen in many malignant disorders, such as
disorders in which hyposplenism has been clearly defined and associ- Hodgkin disease. Rarely, anatomic abnormalities will cause spleno-
ated with a risk for infection are systemic lupus erythematosus, megaly. Splenomegaly is important to investigate because it is fre-
rheumatoid arthritis, sarcoidosis, systemic vasculitis, ulcerative colitis, quently the presenting finding of a serious disorder whose earlier
celiac disease, amyloidosis, chronic graft-versus-host disease, masto- recognition and treatment may prevent significant long-term morbid-
cytosis, and congenital and acquired immunodeficiency. The diseases ity and mortality. The diseases associated with splenomegaly are
themselves and the immunosuppressive therapies that are used in detailed in Table 160.3. Patients with splenomegaly do not necessarily
their management may contribute to the risk for infection in these have hypersplenism, and patients with hypersplenism may indeed
conditions. Immunization with polysaccharide antigens and recogni- have normal-sized spleens, such as those seen in ITP.
tion of the risk of bacterial infection are important steps in reducing Hypersplenism refers to nonimmune, indiscriminate destruction of
the risks of splenic hypofunction. the formed elements of the blood by a spleen that is usually enlarged,
Splenomegaly and the production of autoantibodies such as affected by portal hypertension, or both. The bone marrow is hyper-
antiplatelet or antiphospholipid antibodies, are features of the plastic, and the peripheral blood cell counts are decreased because of
acquired immunodeficiency syndrome (AIDS). In the late stages of destruction of mature formed elements. Splenectomy corrects the
AIDS, atrophy of lymphoid follicles and depletion of T-cell–depen- cytopenia. Any of the formed elements of the blood—erythrocytes,
dent areas are common. It is not clear that impairment of phagocytic neutrophils, or platelets—can be affected alone or in combination.
function is a component of splenic atrophy in AIDS. Splenic hypertrophy in cirrhosis is due to an increase in splenic
macrophages and their activity. Because the normal function of
splenic macrophages is to remove senescent cells, this is an exaggera-
Therapy-Induced Splenic Hypofunction tion of a physiologic process.
Hypersplenism develops in patients who receive chronic transfu-
Radiation therapy affects splenic function depending on the dose sions, and there are several components that contribute to the
administered. In general, phagocytic cells are not affected by irradia- development of hypersplenism. The antigenic load of allogeneic
tion, but lymphoid cells are extremely sensitive. B-cell function is transfused cells stimulates the immune system. Additionally, trans-
nearly ablated with as little as 500 cGy. T-cell lymphoblastogenesis is fused cells have shorter survival than normal red cells (mean of 60
eliminated by administration of 3000 cGy. With doses of 2000 cGy, instead of 120 days, unless specially prepared neocytes are used),
splenic hypofunction is usually transient because the macrophages which increases the work of splenic macrophages. Finally, iron
and splenic stroma are not affected, and circulating B and T lympho-
cytes can repopulate the splenic follicles. Permanent splenic hypo-
function may develop with doses of 4000 cGy or higher. The risk for Timing of Return to Contact Sports in Athletes Who Have Had
infection is significant after such therapy. Infectious Mononucleosis
Corticosteroid therapy impairs the affinity of the Fc receptors of
splenic macrophages for opsonized IgG and decreases the adhesive- An 17-year-old male high school student is diagnosed by his primary
ness of granulocytes and monocytes. This results in an acute phar- care physician with infectious mononucleosis. The patient is concerned
macologic splenectomy, even at commonly administered therapeutic about the upcoming soccer season and wants to be able to start
dosages. The function of the Fc receptors on hepatic, pulmonary, and training with the team in 4 weeks.
bone marrow macrophages is far less affected than that of splenic • More than half of patients with infectious mononucleosis develop
macrophages. The acute rise in platelet count or hemoglobin values splenomegaly within the first 14 days of illness.
seen with corticosteroid therapy in ITP or warm autoimmune • Most reports of splenic rupture in the setting of infectious
mononucleosis occur in the first 21 days of illness.
hemolytic anemia is due to decreased clearance of sensitized cells. • There is a paucity of data to support imaging the spleen to
With prolonged therapy, the production of antibodies by splenic document resolution of splenomegaly before returning to contact
lymphocytes is also affected, and splenic function continues to be sports.
impaired. • Noncontact sports may be safely resumed after at least 21
Intravenous IgG appears to decrease the phagocytic function of days from the onset of initial symptoms and contact sports
the spleen by binding to Fc receptors and impeding their recognition should be safe in most cases after at least 28 days. Infectious
of opsonized particles. This is a transient effect because the Fc recep- mononucleosis–associated splenic rupture has been reported as
tors are internalized and recycled, and opsonic function returns to far as 7 weeks after symptom onset.
normal within 2–3 weeks. Occupancy and impairment of function • The timing of return to sports and the risks should be discussed
with the patient, especially if the patient may not have returned to
of Fc receptors is also seen with administration of anti-IgD to baseline after prolonged fatigue.
Rh-positive patients, which induces a transient hemolytic anemia.