[On the question of cutaneous changes associated with paraproteinemia. Light- and electron-microscopic study (author's transl)].

This report deals with a case of paraproteinemia (IgG Kappa) associated with skin indurations and yellowish papules on the trunk, edema of the face, and crystals in the cornea. In addition to the absence of elastic fibers and reductions of collagen fibers, light microscopy revealed single and/or multinucleated dermal cells with slight streaky patterning of the cytoplasm. These cells contained some sudanophilic (the greatest quantities of sudanophilic substances were observed in the deep corium) and partly birefringent material. In particular after warming, numerous spherocrystals appeared, which give Maltese cross birefringence. The presence of cholesterol esters can be assumed. The light-microscopic localization of acid phosphatase (incubation in Gomori medium) coincides in part with the distribution of bifringent lipids. Electron microscopy showed the cells with streaky contents to be chiefly histiocytes with numerous cristalline bodies in their cytoplasm. The cristalloids with a periodic inner structure are always surrounded by a single membrane. Identical bodies can be detected in endothelial cells of capillaries and epidermal keratinocytes. After pronase P incubation they disappear completely. We assume that the deposits correspond to phagocytized paraprotein. In addition, some histiocytic cells contain numerous lipid droplets in their cytoplasm. There is disintegration of some cells with crystalline inclusion, particularly in the deep corium. These cells show not only diffuse intracytoplasmic but also extracellular distribution of acid phosphatase activities. Particularly in the pericellular space of such cells numerous "banded structures" appear in connection with collagen degradation probably initiated by lysosomal enzymes. Amyloid could not be detected either light- or electron-microscopically.