Tubulointerstitial nephritis without glomerular crescent formation as an underestimated subgroup of renal involvement among microscopic polyangiitis patients: A case report

Acute interstitial nephritis caused by ANCA-associated vasculitis: a case based review

Antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) typically manifests as rapidly progressive glomerulonephritis with crescent formation. In this report, we present a local case of myeloperoxidase (MPO)-AAV-associated acute interstitial nephritis (AIN), showing slight pauci-immune glomerulonephritis and positive MPO-ANCA. This case is characterized by foot process effacement of podocytes in the glomerulus, a favorable prognosis, and an absence of crescentic formation. To further understand this condition, we conducted a comprehensive literature search on Google Scholar and PubMed, employing both free text words and MeSH terms related to "AAV and AIN." This search yielded 24 cases, which we analyzed for their clinical features, laboratory findings, renal pathological characteristics, and therapeutic outcomes. AAV-associated interstitial nephritis predominantly affects elderly patients and is often associated with anemia, proteinuria, hematuria, and nonspecific manifestations, including fever, anorexia, fatigue, edema, and weight loss. Most of the cases in our review were MPO-ANCA-positive and exhibited isolated interstitial inflammation. These patients typically presented with relatively lower levels of serum creatinine, 24-h urine protein levels, and MPO-ANCA titers. All patients in our study received immunosuppressive therapy, including glucocorticoids, immunosuppressants, and rituximab, with the majority achieving clinical remission. Isolated AIN in the context of AAV is a rare occurrence, but it displays distinct clinical, laboratory, and pathological features. Patients with this presentation show a positive response to immunosuppressive treatment. Nevertheless, the establishment of definitive therapy guidelines for AAV-associated AIN remains uncertain and necessitates further investigation to develop comprehensive treatment guidelines. AIN, particularly when lacking typical glomerulus lesions, may represent a novel subgroup within MPO-AAV warranting additional research and clinical attention. Key Points • This study contributes valuable scientific insights by highlighting that MPO-AAV-associated interstitial nephritis, even without crescentic formation, can exhibit podocyte foot process effacement and respond well to treatment. • The presence of AIN, independent of crescentic glomerulonephritis, suggests the potential emergence of a new subclass within MPA-AAV. • Notably, some cases of MPO-AAV-associated AIN may present with normal levels of Scr (Table 5, cases 5, 6, and 17). • This observation highlights the importance of considering renal biopsy, diagnosis, and therapy in a timely manner to prevent the development of chronic kidney disease (CKD).

Interstitial nephritis without glomerulonephritis in ANCA-associated vasculitis: a case series and literature review

The typical nephrological presentation of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is rapidly progressive glomerulonephritis. AAV-associated interstitial nephritis without apparent glomerular lesions was rare. We reported three local cases of AAV-associated interstitial nephritis without glomerulonephritis confirmed by renal biopsy. Then, a literature search was conducted in PubMed using free text words and MeSH terms related to "AAV and interstitial nephritis". Fifteen cases were included, and their demographics, clinical manifestations, laboratory data, renal pathological features, and treatment response were summarized. AAV-associated interstitial nephritis usually affects elderly patients. The common symptoms include fever, arthralgias, and edema. These patients were mostly MPO-ANCA positive. Pathological lesions in the kidney showed diffuse infiltration of inflammatory cells, edema, tubulitis, and fibrosis in the interstitial area. Various immunosuppressive treatments, including glucocorticoids, immunosuppressants, and rituximab, were used, and most of the patients achieved clinical remission. AAV-associated interstitial nephritis is rare but shows a characteristic clinical phenotype, serological results, and pathogenic lesions. Immunosuppressive therapy showed good efficacy in these patients.