Page 2213 - Hematology_ Basic Principles and Practice ( PDFDrive )

1960 Part XII Hemostasis and Thrombosis

(i.e., 5% × 10 min/95% × 1 min, or a ratio of 50 : 95, or ≈1 : 2). TABLE Differential Diagnosis of Splenomegaly and
With hypersplenism, the splenic blood flow can increase up to fivefold 132.4 Hypersplenism
(i.e., from 5% to 25% of total blood flow). Thus even without an
increase in splenic transit time, 70% or more of the platelets can be Infections
exchangeably sequestered within the spleen. Acute
The most important determinant of the splenic platelet pool is Viral (viral hepatitis, infectious mononucleosis, CMV infection)
the spleen size. The measurement of spleen size can thus be helpful Bacterial (septicemia, salmonellosis, brucellosis, splenic abscess)
in predicting the degree of thrombocytopenia expected from excess Parasite (toxoplasmosis)
platelet pooling in the spleen. For example, if 90% of the platelet Subacute and Chronic
pool is in the spleen (i.e., 10% outside the spleen), the platelet count Subacute bacterial endocarditis
will be reduced by sevenfold because normally, 70% of platelets lie Tuberculosis
outside the spleen. Consequently and as a general rule, even if the Malaria
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spleen is massively enlarged, severe thrombocytopenia (<20 × 10 /L) Kala-azar
is rare. On the other hand, mild thrombocytopenia may be explained Fungal disease
by mild splenomegaly that may not be detectible on physical exami- Inflammation
nation but can be seen with imaging studies. Felty syndrome
SLE
PATHOLOGIC PLATELET SEQUESTRATION: Serum sickness
HYPERSPLENISM Rheumatic fever
Sarcoidosis
ALPS
Definition Congestive Splenomegaly
Intrahepatic
Hypersplenism is a syndrome characterized by splenomegaly and any Cirrhosis
or all of the following cytopenias: anemia, leukopenia, or thrombo- Extrahepatic
cytopenia. Implicit in the definition is that the cytopenias will correct
after splenectomy. Although splenomegaly is almost always present Portal vein obstruction
in hypersplenism, many patients with splenomegaly do not have Splenic vein obstruction
hypersplenism. Hypersplenism usually is the result of an identifiable Hepatic vein occlusion (Budd-Chiari syndrome)
pathologic process, but rarely, the cause of the splenomegaly remains Chronic Passive Congestion
elusive, and the hypersplenism is termed primary. Heart failure
Hematologic Disorders
RBC disorders: hemolytic anemias, thalassemia, sickle cell disorders
Pathogenesis Neoplasia
Malignant
A list of disorders producing splenomegaly and hypersplenism is MPDs
presented in Table 132.4. An increase in the size of the spleen can be Myeloid metaplasia
caused by several mechanisms. Increased workload of the spleen can Polycythemia rubra vera
be caused by immunologic stress (infection, inflammation, or an Essential thrombocythemia
autoimmune disorder) or by increased RBC removal (RBC mem- Chronic leukemia
brane disorders, hemoglobinopathies). Portal hypertension also Chronic myeloid leukemia
increases the size of the spleen, producing congestive splenomegaly. Chronic lymphocytic leukemia
Benign and malignant infiltrative disorders may increase splenic size Hairy cell leukemia
(infiltrative splenomegaly) and cause hypersplenism. Some of these Lymphoma
disorders produce thrombocytopenia by more than just hypersplen- Acute leukemia
ism (e.g., BM infiltration with tumor, immune-mediated platelet Malignant histiocytosis
clearance). Thus the demonstration of an enlarged spleen does not Benign
necessarily mean that the cytopenias are caused solely by Hamartoma
hypersplenism. Hemangioma
Thrombocytopenia of hypersplenism is caused primarily by Lymphangioma
increased splenic platelet pooling. A massively enlarged spleen can Fibroma
hold more than 90% of the total platelet mass. In the absence of Storage Diseases
altered platelet production, the total body platelet mass usually is
normal, and the platelet life span is near normal. Usually, the splenic Gaucher disease
transit time remains normal (≈10 minutes), but the absolute number Niemann-Pick disease
of platelets retained within the enlarged spleen is increased. All of Miscellaneous
these platelets remain part of the exchangeable pool. In hypersplen- Amyloidosis
ism, the thrombocytopenia is moderately severe (platelet counts of Cysts
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50 × 10 /L to 150 × 10 /L). Severe thrombocytopenia (<20 × 10 /L) ALPS, Autoimmune lymphoproliferative syndrome; CMV, cytomegalovirus;
suggests another diagnosis. Therefore it is unusual for patients with MPD, myeloproliferative disorder; RBC, red blood cell; SLE, systemic lupus
hypersplenism to have evidence of hemostatic impairment attribut- erythematosus.
able to thrombocytopenia or to need specific interventions to raise
the platelet count. Plasma volume expansion occurs in hypersplen-
ism, but hemodilution plays a relatively minor role in the thrombo- Diagnosis
cytopenia. In some patients with advanced liver disease, impaired
hepatic production of thrombopoietin may contribute to thrombo- Thrombocytopenia is likely to be caused by hypersplenism when
cytopenia in addition to hypersplenism. (1) splenomegaly is present, (2) the thrombocytopenia is mild to
The neutropenia of hypersplenism is caused by an increase in the moderate in severity, (3) a moderately reduced neutrophil count
marginated granulocyte pool, a portion of which is located in the and low-normal hemoglobin levels are found, and (4) there is no or
spleen. The neutropenia of hypersplenism is usually asymptomatic. minimal evidence of impaired hematopoiesis on BM examination.