Light chain renal amyloidosis with prominent giant cells

Clinical diagnosis of amyloidosis may be very challenging because signs, symptoms, and laboratory study results can be highly variable and may overlap with other disease entities. Amyloid has characteristic features on kidney biopsy, involving glomeruli, vessels, and/or interstitium as typically amorphous waxy material that is periodic acid-Schiff pale and Congo Red birefringent under polarized light. Electron microscopy demonstrates characteristic randomly oriented fibrils. However, in rare cases, amyloid may present with atypical morphologic features on kidney biopsy, closely mimicking other histopathologic diagnoses. We present a case of light chain (AL) κ amyloidosis with an unusual inflammatory infiltrate including prominent multinucleated giant cells in the interstitium and at the glomerular hilus. Amyloid was apparent within giant cells on Congo Red staining, as well as on ultrastructural evaluation. Together with prior studies of tumoral nonrenal amyloid and renal amyloid A, we suggest that the amyloid fibril constituents κ and serum amyloid A have some predilection for inciting the rare multinucleated giant cell reaction.