Abstract: PUB198
When ANCA Isn't Vasculitis: Kidney Biopsy Reveals Monoclonal B-Cell Lymphocytosis
Session Information
Category: Onconephrology
- 1600 Onconephrology
Authors
- Abuyaqoub, Hothaifa, University of Michigan, Ann Arbor, Michigan, United States
- Afshinnia, Farsad, University of Michigan, Ann Arbor, Michigan, United States
Introduction
Antineutrophil cytoplasmic antibody (ANCA) positivity often raises concern for ANCA-associated vasculitis (AAV), particularly in patients with kidney dysfunction. However, low-titer or fluctuating ANCA results may be nonspecific. Kidney biopsy is essential to distinguish true glomerulonephritis from alternative diagnoses.
Case Description
A 73-year-old woman with hypertension presented with rising creatinine and new proteinuria. Her baseline creatinine of 0.7–0.9 mg/dL increased to 1.1–1.2 mg/dL with sub-nephrotic proteinuria (UPCR 0.3–0.7 g/g; 24-hour urine protein 0.29 g/day). Urinalysis showed microscopic hematuria without active sediment.
Serologic evaluation revealed fluctuating low-titer MPO-ANCA positivity, with negative PR3-ANCA, ANA, and anti-dsDNA, and normal complement levels. Given concern for early AAV, a kidney biopsy was performed.
Histopathology demonstrated mild chronic changes without evidence of crescentic or immune-complex glomerulonephritis. Notably, focal atypical lymphoid aggregates composed of CD20+ B cells with weak CD5 expression were identified. Hematologic evaluation revealed a lambda-restricted clonal B-cell population consistent with monoclonal B-cell lymphocytosis (MBL). Imaging showed no significant lymphadenopathy.
Discussion
This case underscores the importance of kidney biopsy in patients with ANCA positivity and mild renal abnormalities. Despite initial concern for AAV, biopsy excluded glomerulonephritis and revealed incidental MBL. Urgent immunosuppression for suppression of B-Cell lineage in MBL is not indicated for otherwise stable cases and is reserved for progressive proteinuric infiltrative renal disease. Recognition of this entity prevented unnecessary urgent immunosuppression. Low-titer ANCA should be interpreted cautiously, and biopsy remains critical in establishing diagnosis.