Macular amyloidosis with patchy filamentous degeneration of collagen islands.

Unusual patchy filamentous degeneration of collagen islands, found in a typical case of macular amyloidosis, is described. This phenomenon was found to begin in intact islands scattered among the amyloid islands in the papillary and upper reticula dermis. Since the patches varied in size, they were thought to have grown gradually with time. They were derived from the degeneration of collagen fibrils and demonstrated a tropocollagen-like structure. Although the small patches preserved some characteristic structures of collagen fibrils or tropocollagen, the large patches showed amyloid-like filamentous masses surrounding the collagen islands.