Pauci-Immune Glomerulonephritis (GN) in a Patient with Scleroderma: Importance of Urine Sediment and Kidney Biopsy

Introduction: Up to 10% of patients with systemic sclerosis can develop scleroderma renal crisis (SRC), a syndrome of malignant hypertension, microangiopathic hemolytic anemia, and progressive AKI. Kidney biopsy is not typically done in patients who have classic symptoms, especially with anti-RNA Polymerase III antibodies; however, biopsy can be critical in establishing a diagnosis in patients who have unusual disease features. We present a case of pauci-immune ANCA-associated GN in a patient with systemic sclerosis and a high pre-test probability for SRC. Case Description: A 49-year-old man with untreated scleroderma presented with hemoptysis, fatigue, one week of right upper quadrant abdominal pain, and mild unintentional weight loss over three months. On physical exam, he was afebrile, with a blood pressure of 147/84 mmHg, and had bilateral sclerodactyly, skin tightness, and clear lung fields. Laboratory data showed creatinine of 2.9 mg/dL (from 0.62 mg/dL three months prior), urine protein creatinine ratio of 3.5 g/g, and hemoglobin of 5.1 g/dL with iron deficiency. A CT chest showed extensive bilateral lower lobe airspace opacities with air bronchograms. Bronchoscopy was not consistent with diffuse alveolar hemorrhage. Given worsening renal function (peak creatinine of 4.24 mg/dL) and a positive RNA Polymerase III antibody, a presumptive diagnosis of SRC with superimposed pneumonia was made and he was treated with enalapril and antibiotics. However, his clinic course worsened with recurrent, severe hemoptysis. Urine sediment showed dysmorphic red blood cells, red blood cell casts, and granular casts, prompting kidney biopsy, which showed diffuse pauci-immune crescentic GN. MPO-ANCA titer was positive. Enalapril was stopped and he was treated with IV solumedrol, cyclophosphamide, and plasma exchange with resolution of hemoptysis and improvement of creatinine to 2.33 mg/dL on discharge. Discussion: This case illustrates the importance of examining urine sediment to guide biopsy in patients with suspected SRC, particularly if atypical features are present, and if an alternate diagnosis may require steroid therapy. We add to a body of cases reporting MPO-ANCA vasculitis in patients with systemic sclerosis, potentially identifying an association between scleroderma and small vessel vasculitis.