Case Report: POEMS syndrome secondary to multiple solitary plasmacytomas complicated by hypertriglyceridemia.

Introduction: Polyneuropathy, organomegaly, endocrinopathy, M protein, skin changes syndrome, encompassing polyneuropathy, organomegaly, endocrinopathy, M protein (Monoclonal Immunoglobulin), and skin changes, is a rare systemic disease often marked by diverse endocrine manifestations. Diagnosis typically relies on the detection of monoclonal protein; therefore, cases lacking measurable M-protein may be easily overlooked or misdiagnosed. Case report: We describe a diagnostically challenging case involving a patient in their early fifties who presented with progressive limb numbness and weakness, skin hyperpigmentation, lower-extremity edema, hypothyroidism, and marked hypertriglyceridemia. Despite this multisystem involvement, repeated serum and bone marrow studies failed to demonstrate monoclonal protein. Subsequent imaging and pathological evaluation of the sacroiliac region revealed multiple solitary plasmacytomas with lambda light-chain restriction, which established the diagnosis of POEMS syndrome in the absence of detectable M-protein. The patient experienced notable clinical improvement following bortezomib-based chemotherapy. Conclusion: This case illustrates that POEMS syndrome should be considered even when serum and bone marrow studies do not show monoclonal protein, particularly in the presence of severe hypertriglyceridemia and multisystem injury. Awareness of such atypical presentations is essential to prevent diagnostic delay and to ensure timely initiation of appropriate therapy.