A Silent Virus, a Dangerous Clot: A Case Report of Cytomegalovirus (CMV)-Associated Splanchnic Vein Thrombosis in an Immunocompetent Adult.

Cytomegalovirus (CMV) infection typically presents as an asymptomatic or mild illness in immunocompetent hosts. However, thrombotic complications, though rare, have been increasingly recognized. We report a case of acute superior mesenteric vein (SMV) and portal vein thrombosis with splenic infarction in a previously healthy young adult with primary CMV infection. A 28-year-old male with no significant past medical history presented with acute pain in the left upper quadrant (LUQ) of the abdomen, fever, and diarrhea. Imaging revealed portal vein and SMV thrombosis with hepatosplenomegaly and multiple splenic infarcts. Laboratory evaluation was notable for lymphocytic leukocytosis and elevated liver enzymes. The thrombophilia workup was negative. CMV serology showed positive IgM antibodies and a significantly elevated CMV polymerase chain reaction (PCR) of 1,222 IU/mL, confirming acute primary infection. The patient was treated with anticoagulation and intravenous ganciclovir, resulting in clinical improvement. This report highlights the importance of considering CMV infection in the differential diagnosis of unusual venous thrombosis in immunocompetent young adults. Prompt recognition and treatment are essential to prevent severe complications. Clinicians should maintain a high index of suspicion for CMV-associated thrombosis when evaluating cases of thrombosis in atypical locations.