Kidney Week

Abstract: PUB156

When ANCA Doesn't Play by the Rules: Mixed Glomerulonephritis in Rheumatoid Arthritis

Session Information

• Publication Only

Category: Glomerular Diseases

• 1402 Glomerular Diseases: Clinical, Outcomes, and Therapeutics

Authors

• Patel, Harshil Nitinkumar, Mercy Fitzgerald Hospital, Darby, Pennsylvania, United States

Harshil Nitinkumar Patel, MD

• Agrawal, Bhavika Vijay, Mercy Fitzgerald Hospital, Darby, Pennsylvania, United States

Bhavika Vijay Agrawal, MD

• Naseem, Rabia, Mercy Fitzgerald Hospital, Darby, Pennsylvania, United States

Rabia Naseem, MD

• Bhatt, Tulsi, Mercy Fitzgerald Hospital, Darby, Pennsylvania, United States

Tulsi Bhatt, MD

Introduction

ANCA-associated vasculitis (AAV) classically presents as pauci-immune crescentic glomerulonephritis. Atypical features—including positive ANA, hypocomplementemia, and immune complex deposits on biopsy—can obscure diagnosis and raise concern for lupus or infection-related glomerulonephritis. We report a case of MPO-ANCA crescentic GN with mixed features in a patient with rheumatoid arthritis (RA), highlighting the diagnostic complexity and management approach.

Case Description

54-year-old woman with seropositive RA (off methotrexate 2 months) presented with hemoptysis, fatigue, weight loss, and dark urine. Creatinine peaked at 5.7 mg/dL (baseline 0.7) with nephrotic-range proteinuria (UPCR 3.8–4.5 g/g) and microscopic hematuria. Lab were significant for elevated MPO-ANCA, PR3 and anti-GBM negative, ANA 1:320 homogeneous, elevated RF and anti-CCP, low C4, normal C3, negative anti-dsDNA. Infectious workup (AFB, HIV, hepatitis) was negative. Chest imaging showed bilateral patchy consolidations without cavitation. Kidney biopsy demonstrated diffuse crescentic GN with fibrinoid necrosis, endocapillary hypercellularity, focal collapsing features, and acute interstitial nephritis. Immunofluorescence showed scattered mesangial IgG and C3 without a full-house pattern; EM confirmed sparse mesangial immune complex deposits. Pulse methylprednisolone followed by prednisone 60 mg/day, and rituximab were initiated. Creatinine improved at discharge; hemoptysis resolved without dialysis.

Discussion

This case illustrates atypical AAV with ANA positivity, hypocomplementemia, and mesangial immune complex deposition. MPO-ANCA, may be detected in RA without clinical vasculitis, but true AAV with pulmonary-renal syndrome is uncommon.In RA patients with AKI, hematuria, pulmonary symptoms, or systemic decline, clinicians should maintain suspicion for superimposed AAV rather than attributing findings solely to RA or medications. Up to one-third of ANCA GN biopsies may show low-level immune deposits. Sparse mesangial IgG/C3 deposition does not exclude AAV. “Pauci-immune” does not necessarily mean “completely immune deposit–negative.” Negative HIV testing and biopsy context support secondary collapsing injury related to inflammatory vasculitic disease. Prompt induction with corticosteroids and rituximab can stabilize renal function and resolve pulmonary involvement even in diagnostically complex presentations.