Immune Complex Tubulointerstitial Nephritis: An Unusual Presentation of Anti-LRP2 Nephropathy
- AKI: Mechanisms - II
November 04, 2022 | Location: Exhibit Hall, Orange County Convention Center‚ West Building
Abstract Time: 10:00 AM - 12:00 PM
Category: Acute Kidney Injury
- 103 AKI: Mechanisms
- Fawad, Fnu, University of Kentucky, Lexington, Kentucky, United States
- Ayach, Taha, University of Kentucky, Lexington, Kentucky, United States
- Collins, A. Bernard, Massachusetts General Hospital, Boston, Massachusetts, United States
Anti-LRP2 nephropathy/anti-brush border antibody (ABBA) disease is a recently described immune complex tubulointerstitial nephritis. It is characterized by renal failure with tubular injury, tubular basement membrane immune deposits and circulating antibodies to proximal tubular brush border. The antigen target for ABBA has recently been identified as LDL receptor-related protein 2 which is present in proximal tubular brush border. We present a case of immune complex TIN with biopsy features suggestive of anti-LRP2 nephropathy but no ABBA in the serum.
A 76-year-old male with past medical history of myasthenia gravis was evaluated for unexplained worsening of renal function. His sCr had increased from 1.2 to 2.7 over 1.5 years. He had microscopic hematuria and minimal proteinuria. Serological workup showed positive ANA with a titer of 1:80 with speckled pattern, negative anti dsDNA, normal C3 and C4, negative ANCA, MPO and PR3 and normal IgG 4 level. Kidney biopsy was performed which showed chronic tubulointerstitial nephropathy with extensive IgG deposits and segmental membranous nephropathy. IF microscopy showed extensive TBM deposits of IgG, in addition to segmental membranous nephropathy. This combination of findings was felt to be suggestive of anti-LRP2 nephropathy. However, patient’s serum when tested, was negative for ABBA. Patient was started on prednisone 60 mg daily which was tapered two months after initiation due to complicating nocardia infection. No further disease specific treatment was given for his ABBA disease, but on follow up his renal function has remained relatively stable with most recent sCr of 2.6.
Although biopsy features in this case were suggestive of anti-LRP2 nephropathy, serum was negative for ABBA. It is noteworthy that testing for ABBA is not commercially available and was done in a research laboratory and sensitivity is not well established. Absence of serum ABBA in this case could also indicate the possible onset of spontaneous remission, which will also explain the relatively stable renal function more than one year after diagnosis. It is also possible that antibodies to antigens other than LDL receptor-related protein 2 may be playing a role in the pathophysiology of ABBA disease. Our case highlights the need for further investigation into the association of ABBA with anti-LRP2 nephropathy.