A 53-year-old man presented with POEMS syndrome characterized by a solitary plasmocytoma and an angiofollicular lymph node hyperplasia similar to that observed in Castelmann's disease. Two features were prominent: first, a severe hypertriglyceridemia, which could have been related to autoimmune suppression of lipoprotein lipase activity; second, a marked immunostaining of myelin sheaths with occasional widening of myelin lamellae. These data, added to the complete regression of the neuropathy immediately following surgical removal of the plasmocytoma (with subsequent irradiation) suggested that the paraprotein was responsible for the neuropathy.