De novo AA amyloidosis in a transplant kidney

Abstract

BACKGROUND: Amyloidosis is defined by extracellular deposition of amyloid: abnormally folded proteins characterised by positive staining with Congo red and apple-green birefringence under polarised light and nonbranching, rigid fibrils 8-12 nm on electron microscopy (EM). AA amyloidosis, the second most common type, typically involves the kidneys when systemic. However, de novo amyloidosis in renal transplantation is rare, usually occurring concurrently with active chronic inflammation. We aim to describe a case of de novo AA amyloidosis in a transplanted kidney. Case presentation: A 71-year-old man presented with acute kidney injury with a history of renal transplant secondary to autosomal dominant polycystic kidney disease, bronchiectasis, gout and recent long COVID. He deteriorated, requiring hospital admission for Pneumocystis jirovecii pneumonia and SARS-CoV-2 infection. Renal transplant biopsy was performed, showing amorphous eosinophilic material consistent with amyloid on Congo red stain and EM. Mass spectrometry confirmed de novo transplant kidney AA amyloidosis. Chronic inflammation secondary to bronchiectasis was implicated. The patient received antimicrobials and continued regular transplant immunosuppression. He was discharged home with regular haemodialysis, Palliative Care input, home supplemental oxygen, fluid restriction and renal diet. This rare case highlights the importance of both management of chronic inflammation and appropriate typing of amyloidosis to guide therapy.