HMS is considered a distinct entity from the splenomegaly that results from acute malarial parasitemia. The pathogenesis is believed to result from overproduction of immunoglobulins in response to repeated infection with malaria, particularly IgM, which aggregate in immune complexes within the spleen. As a result of delayed clearance from the reticuloendothelial tissue, splenomegaly develops and persists. Parasitemia is uncommon. The spleen size has been shown to be directly correlated to the serum level of IgM. Genetic predispositions have been noted among individuals with the human leukocyte antigen (HLA)-DR2 haplotype.
Although the highest prevalence of HMS is reported at 80%-85% in Papua New Guinea, other locations also report a significant prevalence, including northern Nigeria (40%), Kenya (41%), and Ghana (76%). A diagnosis of HMS should be considered in individuals who present from endemic areas with longstanding splenomegaly.
Diagnostic criteria for HMS include the following major criteria:
Persistent splenomegaly (>10 cm below the costal margin)
Elevated antimalarial antibody levels
IgM titer >2 standard deviations above the mean
Favorable response to long-term malaria prophylaxis
Minor criteria include the following:
Hepatic sinusoidal lymphocytosis (liver biopsy histology)
Normal humoral immune responses to antigenic challenge (phytohemagglutinin stimulation)
Occurrence within family tribes
Long-standing untreated HMS is often fatal and has been associated with premalignant conditions. It can evolve into chronic lymphocytic leukemia, hairy cell leukemia, or splenic lymphoma with villous lymphocytes (SLVL). At times, HMS is difficult to distinguish from lymphoproliferative disorders. Many serologic markers are similar between SLVL and HMS, including high antimalarial antibodies and IgM levels.
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Cite this: Rebecca Winderman, Natalie Banniettis, Simon S. Rabinowitz. Chronic Splenomegaly in a 10-Year-Old Boy - Medscape - Apr 23, 2018.