Electron microscopy in the diagnosis of amyloidosis.

Amyloidosis defines a pathological condition in which organ and tissue damage is related to the extracellular deposition of amyloid fibrils, deriving from specific proteins, the amyloid precursor proteins. More than 25 different precursor proteins are associated with different forms of amyloidosis, which are summarized in Tables 1 and 2. The modern nomenclature is based on the type of amyloid protein involved (Sipe et al., 2010). A subdivision into systemic and localized amyloidosis is also frequently adopted and is relevant in clinical practice and histopathology (Picken, 2010). However, although certain amyloid forms are exclusively localized (e.g. neurodegenerative A┚), others (e.g. AL) can be either systemic or localized. Prions are usually considered a distinct clinico-pathological entity in connection with their peculiar infectious nature.