Fig. 46.7. A young African woman with gross hepatosplenomegaly due to TSS. (From Itakura 1995).

Fig. 46.8. The spleen and liver from a case of TSS. The cut surface of the spleen was a dark, meaty-red color and follicles were not apparent. The liver shows preservation of the normal lobular structure. (From Itakura 1995).

Tropical Splenomegaly

Enlargement of the spleen is common in many tropical countries: it has many causes, including those which are not "tropical;" such as leukemia and other blood dyscrasias, and infections, including measles (rubeola), histoplasmosis, trypanosomiasis, and tuberculosis, as well as many other bacterial infections. Neoplasms, such as lymphoma and metastases from many primary tumors, and storage diseases such as Gaucher's disease also cause splenomegaly. The differential diagnosis list is very long and must include many tropical diseases, such as echinococcosis, schistosomiasis, malaria, leishmaniasis (kala azar), other parasitic diseases, typhoid fever, melioidosis, and the hemoglobinopathies.

While the clinical and laboratory findings may result in an exact diagnosis, the imaging of splenomegaly is usually nonspecific. To all the possible causes must be added the tropical splenomegaly syndrome (TSS), in which the spleen is enlarged, perhaps considerably and particularly in children, and for which there is no proven etiology.

Synonyms

Big spleen disease. TSS Gross splenomegaly of obscure origin. Idiopathic splenomegaly. Bengal splenomegaly. Cryptogenic splenomegaly. Hypersplenism of the tropics. The lymphoproliferative syndrome.

Definition

Tropical splenomegaly (Figs. 46.7, 46.8) is enlargement of the spleen without specific cause, usually with hepatomegaly, coagulopathy, thrombocytopenia, anemia, and raised levels of immunoglobulin at least two standard deviations above the local mean. The histopathological criteria refer to polyclonal macroglobulinemia and clusters of lymphocytes in the hepatic sinusoids; hepatic sinusoidal lymphocytosis can be used to predict the size of the spleen. All definitions also refer to a high level of immunity to malaria.

Geographic Distribution

Tropical splenomegaly syndrome is widespread throughout Africa, India, and Southeast Asia. North African and Mediterranean countries, Hong Kong, and New Guinea also host this unexplained syndrome, and it is said to occur around Los Angeles (USA), but this may reflect the very large number of immigrants in this area.