Splanchnic Vein Thrombosis as the Initial Manifestation of Lambda Light Chain Multiple Myeloma.

We present the case of a 67-year-old man who developed superior mesenteric vein thrombosis (SMVT) as the initial manifestation of IgD lambda and lambda light chain multiple myeloma (LCMM). He initially presented with abdominal pain and was found to have SMVT without identifiable thrombophilic risk factors. Persistent macrocytosis, unexplained renal dysfunction, and mild anemia prompted further evaluation, revealing markedly elevated serum free lambda light chains, suppressed immunoglobulins, and a bone marrow biopsy confirming LCMM. This case highlights the importance of considering plasma cell dyscrasias in patients with unprovoked thrombosis at atypical sites, particularly when accompanied by subtle hematologic or renal abnormalities. Early recognition of LCMM is essential given its aggressive nature and potential for diagnostic delay due to absent or minimal findings on standard serum protein electrophoresis.