Lichen amyloidosus. Ultrastructure and pathogenesis.

The ultrastructure of six cases of lichen amyloidosus was studied with special attention to epidermal keratinocytes and the role of tonofilaments as precursors of fibrils of amyloid. Through the process of apoptosis, keratinocytes undergo degeneration and become filamentous cells and then filamentous masses or Civatte bodies. These bodies then drop into the dermis through a damaged basement membrane. In the papillary dermis, islands of amyloid become closely associated with Civatte bodies. In some cases, conversion to straight nonbranching filaments, characteristic of fibrils of amyloid, was found within whorled, densely packed filamentous masses. The transformation into fibrils of amyloid was not observed in keratinocytes or Civatte bodies situated in the epidermis. This final step of conversion may be aided by dermal fibroblasts that are frequently lodged around deposits of amyloid.