POEMS Syndrome Without a Detectable Monoclonal Peak: The Critical Role of VEGF and Bone Marrow Biopsy in Diagnosis.

Polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder, skin changes (POEMS) syndrome is a rare disorder that is frequently misdiagnosed due to its heterogeneous presentation and overlap with chronic inflammatory demyelinating polyneuropathy (CIDP). Diagnosis requires the presence of polyneuropathy and a monoclonal plasma cell disorder, along with additional major and minor criteria. We present a 73-year-old woman with progressive weakness, volume overload, and weight loss, initially diagnosed with CIDP. Despite IVIG therapy, her symptoms worsened. Notably, no monoclonal peak was detected on serum protein electrophoresis (SPEP) or immunofixation, complicating the diagnosis. However, markedly elevated vascular endothelial growth factor (VEGF) levels (11.245 pg/mL) and bone marrow biopsy findings of a monoclonal plasma cell disorder confirmed POEMS syndrome. She also developed multiple thromboembolic events, highlighting the syndrome's prothrombotic nature. This case underscores the importance of maintaining high suspicion for POEMS syndrome in the setting of undifferentiated polyneuropathy, even in the absence of a monoclonal peak on SPEP. VEGF measurement and bone marrow biopsy are crucial for diagnosis in such cases. Early recognition and treatment, including plasma cell-directed therapy and anticoagulation, are essential to improving patient outcomes and preventing irreversible complications.