Electron microscopy is usually reserved for cases in which the stains at the light microscopic level are non-diagnostic or for cases with minimal deposits, as in the kidney.
All amyloids have a similar ultrastructure.
Microscopically, most have an associated lymphoplasmacytic infiltrate with multinucleated giant cells. Wedge resection or fine needle aspiration has been used to make a diagnosis. AA was thought to be a possibility in this patient, who had rheumatoid arthritis, but an immunoperoxidase stain for AA was negative, and the nodule is presumed to be the AL type. AL is the product of a clonal proliferation in myeloma and other lymphoproliferative diseases. In two cases, rearrangement of the heavy-chain immunoglobulin gene of cells from the central part of the tumor indicated the presence of a monoclonal population of B cells.