[Diffuse normolipidemic plane xanthomatosis and monoclonal dysglobulinemia. A case with anti-lipoprotein activity of monoclonal immunoglobulin and hypocomplementemia].

INTRODUCTION: Diffuse normolipaemic plane xanthomatosis associated with monoclonal dysglobulinaemia has been recognized as a clinical entity for more than 30 years. Antilipoprotein activity has been reported in certain cases with monoclonal immunoglobulinaemia or hypocomplementaemia.

CASE REPORT: A 64-year-old woman developed simultaneously diffuse normolipaemic plane xanthomatosis and monoclonal IgG kappa dysglobulinaemia. This paraprotein was initially associated with monoclonal gammapathy of undetermined signification (called "benign") before evolving into a myeloma. This aggravation was associated with an expansion of the skin lesions. Immunological exploration demonstrated the presence of IgG-lipoprotein complexes in the plasma and hypocomplementaemia suggesting incomplete activation of the classical pathway (low CH50 and fraction C4).

DISCUSSION: According to the literature, the most probable hypothesis for the pathogenesis of the xanthomatosis-dysglobulinaemia association is a specific interaction between the monoclonal immunoglobulin and lipoprotein metabolism. In normolipaemic forms, the immunoglobulin-lipoprotein complexes are recognized by "waste-receptors" and accumulate in the dermal macrophages while the mechanism of lipoprotein captation in the other types of cells remains normal, explaining the absence of hyperlipidaemia.