Abstract: TH-PO617

Predominantly Vascular AL Amyloidosis Mimicking Vascular Hyalinosis on Renal Biopsy – A Diagnostic Pitfall

Session Information

Category: Nephrology Education

  • 1302 Fellows and Residents Case Reports

Authors

  • Iluyomade, Anthony F., University of California Davis Medical Center, Sacramento, California, United States
  • Madan, Niti, University of California, Davis, Sacramento, California, United States
  • Jen, Kuang-Yu, University of California, Davis, Sacramento, California, United States
Background

Vascular-limited renal amyloidosis accounts for ~5% of AL amyloidosis cases. In this form, patients often present with minimal proteinuria, making the diagnosis clinically challenging. Histologically, vascular hyalinosis mimics vascular amyloidosis and may lead to errors in diagnosis, especially in elderly patients with a history of hypertension where chronic vascular disease is expected on biopsy.

Methods

An unusual case of predominantly vascular AL amyloidosis with nephrotic range proteinuria and histologic appearance indistinguishable from vascular hyalinosis is presented. A 75-year-old male was noted to have normal serum creatinine but nephrotic range proteinuria. Physical examination was significant for anasarca. Further work-up showed elevated serum free light chains with lambda predominance. A kidney biopsy was performed to characterize renal involvement.The biopsy contained 12 glomeruli, 2 of which were globally sclerotic. All the non-sclerotic glomeruli showed normal histology with no evidence of amyloid deposition. Severe chronic vascular disease was noted with prominent arteriosclerosis in larger caliber vessels. Smaller caliber vessels including small arteries and arterioles exhibited mural deposition of hyaline-like material that stained strongly for PAS but showed minimal silver staining. Congo red stain revealed that this material within the vessels was positive, confirming vascular amyloid deposition. No Congo red staining was seen in any of the glomeruli. Ultrastructural examination confirmed the widespread presence of amyloid within the vessels. Rare and minimal amyloid deposition was noted in the glomerular capillary loops and mesangium. He was started on CYBORD (Cyclophosphamide, Bortezomib and Dexamethasone), a repeat serum immunofixation showed undetectable overt evidence of monoclonal protein.

Conclusion

This case of predominantly vascular renal amyloidosis was indistinguishable from vascular hyalinosis based on routine light microscopic stains for renal biopsy, showing similar intense PAS positivity in the amyloid as normally seen in hyaline arterio- and arteriolosclerosis. However, Congo red stain and electron microscopy confirmed the presence of amyloid. Vascular-limited or predominantly vascular renal amyloidosis can be mistaken for vascular hyalinosis in such instances, resulting in a diagnostic pitfall.