Primary antiphospholipid syndrome: a cause of fever of unknown origin.

Antiphospholipid syndrome (APS) is defined as the occurrence of thrombosis, recurrent miscarriage, or both in association with laboratory evidence of persistent antiphospholipid antibodies. Owing to protean manifestations and laboratory studies, the diagnosis may be difficult. Because the other signs and symptoms of thrombosis are predominant, prolonged fever is not usually the main clinical finding. We describe a patient who presented with fever of unknown origin (FUO) and was found to have thromboses of the splenic vein, the superior mesenteric vein, and the portal vein due to the primary antiphospholipid syndrome. We also reviewed the medical literature (Medline 1966-2001), including the main FUO series of the previous 40 years, and laparotomy series for FUO. We conclude that although very rare, primary APS and thrombosis may present with FUO. APS should be considered in the differential diagnosis of prolonged fever associated with thrombosis.