Unusual morphology of amyloid cast nephropathy in renal biopsy portending poor prognosis

Abstract

Light chain cast nephropathy is the most frequent form of renal disease in plasma cell neoplasm showing precipitation of monoclonal immunoglobulin light chains in the lumen of the distal tubules. This has a typical morphological feature characterised by the presence of a fractured cast. In this article, we report an unusual case of light chain cast nephropathy exhibiting amyloidogenic potential with lamellated, spiculated appearance. These casts were positive for periodic acid–Schiff and Jones’ silver stain, fuchsinophilic in Masson trichrome stain and showed apple-green birefringence under polarised light in Congo red stain. Complete haematological evaluation confirmed the presence of underlying plasma cell myeloma. The connotation of intratubular amyloid cast lies in the fact that this may represent an early phenomenon during the development of light chain cast nephropathy-associated systemic amyloidosis and may precede the formation of light chain amyloid in renal or extrarenal location.