Type III hyperlipoproteinemia with xanthomas and multiple myeloma.
BACKGROUND: Type III hyperlipoproteinemia usually results from an inherited defect in the composition of apolipoprotein E and is associated with atherosclerosis. An acquired form of the type III phenotype may rarely be associated with myeloma and immunoglobulin-lipoprotein complexes. OBSERVATION: We present the case of a 72-year-old man with a history of well-controlled, unclassified hypercholesterolemia and hypertriglyceridemia, without evidence of atherosclerotic disease. He subsequently developed refractory dyslipidemia, palmar crease, and tuberous xanthomas. Type III hyperlipoproteinemia was confirmed, and nonclassic defective apolipoprotein E. Common secondary causes of hyperlipidemia were ruled out. A workup for malignancy revealed monoclonal IgA gammopathy. Immunostaining confirmed IgA antibodies complexed to the patient's very low-density lipoprotein (VLDL) fraction, causing gross impairment of VLDL metabolism. Conventional therapy for type III hyperlipoproteinemia was attempted but ineffective. Thus, chemotherapy was initiated for his myeloma, with subsequent lowering of his IgA, cholesterol, and triglyceride levels, and improvement of his xanthomas. CONCLUSION: There are several unusual features to this case. Planar xanthomas can be associated with myelomas, but usually in the setting of normal lipids. Type III hyperlipoproteinemias are not usually refractory to standard therapy and are only rarely associated with IgA myeloma. IgA antibodies complexed to the patient's VLDL caused gross impairment of VLDL metabolism. The patient's apolipoprotein E genotype (heterozygote E2/E3) is not typical for expression of the heritable type III phenotype (homozygote E2/E2). These features support a causal relationship between this patient's multiple myeloma and type III hyperlipoproteinemia rather than two independent, coexistent conditions.