Antineutrophil Cytoplasmic Antibody–Associated Vasculitides in Systemic Sclerosis: A Unique Clinical Overlap With Significant Implications for Treatment and Outcomes

OBJECTIVE: Systemic sclerosis (SSc) is an autoimmune disease characterized by autoantibody production, fibrosis, and vasculopathy. The coexistence of antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides (AAV) in SSc is rare and poorly characterized, with limited data on the impact of treatments, particularly high-dose glucocorticoids (GCs), on both conditions. This study aimed to describe the clinical phenotype, management, and outcomes of patients with overlapping SSc and AAV. METHODS: We conducted a multicenter retrospective study in 18 French centers, including patients who met the 2013 American College of Rheumatology (ACR)/EULAR criteria for SSc and the 2022 ACR/EULAR criteria for AAV. Clinical, biologic, and radiologic data were collected. RESULTS: We included 30 patients (median age 51.5 years, 83% female). SSc preceded AAV in all cases; 27% had diffuse cutaneous SSc, whereas 73% had limited cutaneous SSc. Anti-Scl70 antibodies were detected in 50%, and interstitial lung disease (ILD) was present in 80%, predominantly with a fibrosing nonspecific interstitial pneumonia pattern (54%). AAV was microscopic polyangiitis in 90%, with myeloperoxidase (MPO)-ANCA positivity in 93%. Renal involvement was common (76%), with a median serum creatinine level of 170 μmol/L (interquartile range [IQR] 120-361 μmol/L) and proteinuria (urine protein to creatinine ratio of 2 g/g creatinine [IQR 0.9-2.3 g/g creatinine]). All patients received GCs in combination with cyclophosphamide (50%) or rituximab (47%). No cases of scleroderma renal crisis were observed. SSc manifestations, including ILD and skin involvement, remained stable during follow-up. CONCLUSION: AAV, predominantly microscopic polyangiitis with MPO-ANCA, can occur in SSc, particularly in patients with fibrosing ILD and anti-Scl70. Standard vasculitis treatments appear to be effective and do not worsen outcomes in SSc.