Acquired vitamin B6 deficiency in POEMS: a marker of disease activity and cause of neuropathy?

Background POEMS syndrome is a rare, life-threatening multisystem disease driven by clonal plasma cell proliferation and characterised by disabling neuropathy, a monoclonal plasma cell disorder and diagnostic paraneoplastic features. Although vascular endothelial growth factor (VEGF) is a key diagnostic marker and correlates with disease activity, it is not the central mediator and the specific pathomechanism for the characteristic distal sensorimotor neuropathy remains elusive. Pyridoxal 5’-phosphate (PLP), the active form of vitamin B 6 , is an essential cofactor for human biological processes; its deficiency is known to cause distal sensorimotor neuropathy. Methods Following reports of B6 deficiency in POEMS syndrome, 50 sequential patients at our centre (18 active, 32 in remission) were tested for PLP deficiency between September 2023 and July 2024. Results Active POEMS patients demonstrated significantly lower plasma PLP concentrations (median 9.5 nmol/L) compared with those in treated remission (median 36 nmol/L; p