Peripheral nerve, Amyloidosis

Amyloidosis is a disease associated with numerous inflammatory and inherited disorders that produce extracellular deposits of proteins abnormally folded into beta-pleated sheets (i.e. amyloid). Amyloid deposition in peripheral nerve can be hereditary (due to mutations in various proteins including transthyretin, gelsolin, apolipoprotein A1, and prion protein), as in this case, or acquired (for example, due to a plasma cell dyscrasia producing amyloidogenic light chains). Hereditary amyloidoses can be neuropathic (as in this case) or non-neuropathic.

Microscopically, amyloid appears as amorphous extracellular eosinophilic deposits that stain with Congo red; when viewed under polarized light, the stain shows apple-green birefringence. Prognosis of systemic amyloidosis is generally poor.