Two different pathogenetic pathways in lichen amyloidosus and macular amyloidosis.

In lichen amyloidosus (LA) and macular amyloidosis (MA), small amyloid deposits occur in the upper papillary dermis. Previous electron-microscopic studies have indicated an epidermal origin of the amyloid, where degenerating keratinocytes drop into the dermis and undergo transformation to amyloid. While this mechanism seems possible at least in MA, we suggest an alternative pathogenetic pathway in LA, in which amyloid fibrils seem to form on the dermal surface of living basal keratinocytes. It is possible that the different morphology of the amyloid in LA and MA is explained by partially different pathogenetic mechanisms although the amyloid in both conditions may be chemically closely related.