[Dacie syndrome and other splenomegalies without apparent cause]

Some enlarged spleens do not seem to be related with known pathogenetic mechanisms (passive congestion, functional workload, malignant infiltration and inflammatory or storage disorders). Non-tropical idiopathic splenomegaly (Dacie's syndrome) is a form of hypersplenism of unknown origin that evolves into a non-Hodgkin lymphoma, after a variable interval, in 20% of the patients. Tropical idiopathic splenomegaly (or hyperreactive malarial splenomegaly) develops when a chronic malarial challenge triggers an abnormal immunological response consisting in decreased suppressor T lymphocytes and increased amounts of circulating immunoglobulin M and immunocomplexes, which are cleared by the splenic macrophages. This peculiar response to malaria seems to be linked to particular HLA antigens. Other confusing splenomegalies are seen in Felty's syndrome, in populations subjected to recurrent infections, and in some families. Overlapping findings and diseases suggest chronic antigenic stimulation as a common feature, with diverse responses depending on the host. A small percentage (probably less than 3%) of normal individuals has minimal splenomegaly without any clinical significance.