Unusual amyloid polyneuropathy with predominant lumbosacral nerve roots and plexus involvement.

We report a 25-year-old patient with a progressive asymmetric peripheral neuropathy of the distal lower limbs. Imaging studies showed enlargement of lumbosacral roots, plexus, and proximal sciatic nerve. Sacral plexus biopsy revealed amyloidosis associated with endoneurial edema. Immunohistochemistry with anti-prealbumin, serum amyloid A, and immunoglobulin light chain antisera failed to label the amyloid.