Cutaneous xanthoma in association with paraproteinemia in the absence of hyperlipidemia.

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Abstract
In the present report we describe a patient with multiple myeloma and long-standing paraproteinemia who developed xanthoma in the absence of an elevation in plasma cholesterol or triglyceride concentrations. Studies demonstrated that our patient's monoclonal IgG antibody interacted with apoprotein B-100. The LDL-antibody complex isolated from our patient did not affect the degradation of LDL by human fibroblasts, indicating that while IgG derived from our patient interacted with LDL it did not alter the metabolism of this lipoprotein by the LDL receptor pathway. Since the LDL receptor pathway is the major route of LDL metabolism, this probably explains why our patient was not hyperlipidemic. In contrast to an absence of effect on the LDL receptor, our patient's LDL-antibody complex stimulated cholesterol esterification within macrophages indicating the uptake and degradation of the LDL-antibody complex. The LDL-antibody complex inhibited the degradation of acetyl LDL by macrophages (scavenger pathway), demonstrating that our patient's LDL-antibody complex was recognized as a modified LDL. Moreover, mixing Ig from our patient with normal LDL also resulted in the normal LDL increasing the esterification of cholesterol by macrophages. One can hypothesize that our patient's monoclonal IgG-LDL complex interacted with the macrophage scavenger receptor, thereby resulting in the occurrence of xanthoma in the absence of hyperlipidemia.