ANСA-associated vasculitis and IGG4-associated disease - the same or different diseases?

Abstract

IgG4-related disease (IgG4-AD), is a fibro-inflammatory condition characterized by an increase of serum IgG4 and infiltration of the tissue of affected organs by IgG4-positive plasma cells. There is a significant cross between IgG4-AB and antineutrophilic cytoplasmic antibodies (ANCA) – associated vasculitis (AAV) because of clinical and morphological features of both pathologies. A positive ANCA test is considered highly specific for AAV and excludes other forms of systemic diseases. However, a number of recent publications have demonstrated a combination of IgG4-AD with positive serum ANCA in patients, which suggests a revision of the role of ANCA as a diagnostic criterion for AAV. In this work, we describe a clinical case of a combination of clinical and morphological markers of IgG4-AD and positive serum ANCA in an 8-year-old girl. She had a combination of lung and kidney injury. Kidney disease was manifested as pyelonephritis and incomplete nephrotic syndrome. Histologically, it was identified a combination of tubulointerstitial nephritis and membranous nephropathy, with severe IgG4 infiltration in the glomerulus. The search for serological markers of systemic diseases revealed a positive test for myeloperoxidase ANCA, which suggested the existence of AAV in the patient. However, the presence of membranous nephropathy, which is an uncharacteristic morphological pattern of AAV, and massive deposition of IgG4 in the kidney tissue suggests a different pathogenetic mechanism in this patient.