Tubular basement membrane amyloid deposition: is it an indicator of renal progression in light chain amyloidosis?

In light chain amyloidosis (LA), the massive glomerular and vascular amyloid deposition leading to interstitial fibrosis/tubular atrophy (IFTA) is thought to be responsible for renal failure. The amyloid deposition in the interstitium and the tubular basement membrane (TBM) has received less attention in the study of LA. We, therefore, collected clinical and laboratory data on patients diagnosed with LA in our Nephrology Department and studied amyloid deposition in the TBM. Twelve LA patients were diagnosed by renal biopsy during a seven-year period. In 4 of the 12, amyloid deposition could also be detected in the TBM. In our first case of a patient with diabetes mellitus, non-amyloid fibrils resembling 'diabetic fibrillosis' were also seen by electron microscopy. Despite the double damage, IFTA was negligible, blood vessels were unaffected, and the glomerular deposition was segmental. In the other three cases, significant (>50%) IFTA and a severely reduced estimated glomerular filtration rate were already detected at the time of diagnosis and amyloid deposition was also observed in the blood vessels. These findings indicate the importance of TBM amyloid deposition in the progression of renal disease. This may represent a late-stage presentation of the disease with a heavy LC burden.

Ibrutinib-induced acute kidney injury via interstitial nephritis.

The introduction of Bruton's tyrosine kinase inhibitor ibrutinib has made a significant progress in the treatment of chronic lymphocytic leukemia and other B-cell malignancies. Due to the reduction of cytokine release, it is effective in chronic graft-versus-host disease, and its use has also been suggested in autoimmune diseases and in prevention of COVID-19-associated lung damage. Despite this effect on the immune response, we report a severe hypersensitivity reaction in a 76-year-old male patient diagnosed with prolymphocytic leukemia. Four weeks after the ibrutinib start, non-oliguric acute kidney injury with proteinuria and microscopic hematuria developed and that was accompanied by lower limb purpuras and paresthesia. Renal biopsy revealed acute interstitial nephritis. Employing 1 mg/kg methylprednisolone administration, serum creatinine decreased from 365 µmol/L to 125 µmol/L at 11 days and the proteinuria-hematuria as well as the purpura, paresthesia resolved. Three months later at stabile eGFR of 56 ml/min/1.73 m2 methylprednisolone was withdrawn and a rituximab-venetoclax treatment was initiated without side effects. We conclude that despite the beneficial effect on cytokines response in Th1 direction, ibrutinib can cause acute interstitial nephritis. Early detection, discontinuation of ibrutinib, glucocorticoid administration may help to better preserve renal function, thereby lowering the risk of potential subsequent kidney injury.