Ultrastructure of skin in primary systemic amyloidosis.

Amyloid masses were found in the dermis of two brothers suffering from primary amyloidosis. The masses consisted of fibrils, composed in turn of twin hollow filaments of amyloid. An amyloid filament appeared as a 3 nm thick lucent core with a 2 nm thick wall. Occasionally 4--6 filaments were packed together in one fibril. The twin filaments were slightly twisted, with a twisting angle of 2.5 degrees and a coiling pitch of 1 160 nm. Wavy shapes of amyloid fibrils were also seen in elastic fibres. Amyloid fibrils were found in elastic fibres, under the basal lamina of the epidermis, sweat gland epithelium and Schwann cells; also around perineural cells, perivascular cells and, in one of the brothers, in collagen fibril bundles. No amyloid fibrils were found under the endothelial basal lamina. It would appear that amyloid fibrils are pathological fibrils belonging to the elastic fibre-basal lamina system.