[Cutaneous-mucous hyalinosis (Urbach-Wiethe disease). Histologic and ultrastructural study of a case]

Hyalinosis cutis et mucosae is a rare genetic disorder, primarily involving skin and mucous membranes, that has been described under various titles as lipoidosis lipoproteinosis and Urbach-Wiethe disease. A 17-year-old girl presented cutaneous macular lesions, skin scars, thickened lips and enlarged firm tongue; hoarseness was known since birth. The labial biopsy specimen was investigated by light and electron microscopy. Histologically there are deposits of amorphous, extra-cellular eosinophilic hyaline material in the upper thickened connective tissue. In the lower part changes are focal with hyaline mantle around the vessels. Histochemical studies have revealed that the deposits were PAS-positive and amylase-resistant, indicating the presence of neutral mucopolysaccharides. Lipid stains were positive, especially in vessel walls. Ultrastructurally hyaline substance is composed of 1 to 2 nm protofilaments, larger ones (5 to 10 nm wide) and amorphous material. Fibroblasts contain in their dilated cisternae amorphous material. A frequent feature is marked multilamination of the capillary basal lamina which is interpenetrated by hyaline substance. Pathogenesis is still unknown but recently it is suggested hyalinosis cutis et mucosae could be a systemic disease of basal lamina.