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

Comparison of the clinicopathological characteristics of children with anti-neutrophil cytoplasmic antibody-associated vasculitis with/without infection at diagnosis

BACKGROUND

Infectious episodes contribute to morbidity and mortality in patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Renal involvement, also known as ANCA-associated glomerulonephritis (AGN), is frequently observed in AAV. Little is known about whether co-infection at initial diagnosis is associated with renal outcome and prognosis in children with AGN.

METHODS

Clinical and prognostic data for children admitted to our center with AAV from January 2001 to August 2023 were analyzed retrospectively. We compared the incidence of end-stage renal disease (ESRD) and mortality according to infection status at initial diagnosis.

RESULTS

A total of 33 children with AGN were included in this study, 22 had an infection at the time of AGN diagnosis. A trend toward higher levels of proteinuria in the infected group than in the non-infected group was observed (p = 0.42). Patients in the infected group had higher creatinine and lower eGFR values than those in the non-infected group (p = 0.09). A significant decrease in HGB was observed in the infected group (p < 0.05). There were no significant differences in the baseline values of ALB and complement c3 between the two groups. A similar proportion of patients in both groups required dialysis at the time of diagnosis (27.3% vs. 31.8%). Patients with infection presented with significantly greater ESR and CRP levels (p < 0.05), and the most commonly infected site was the lung. After 6 months of treatment, compared with those in the non-infected group, the median levels of creatinine and proteinuria were higher in the infected group. Besides, lower levels of eGFR and ALB were also observed in the infected group. 5 (45.5%) and 13 (59.1%) patients died or progressed to ESRD, respectively, in the non-infected group and infected group at the last follow-up.

CONCLUSIONS

Infection at initial diagnosis does not affect the outcomes of children with AGN, although it could lead to a reduction in kidney function.

Proliferative features of IgG4-related disease

IgG4-related disease is an immune-mediated disease that can lead to substantial morbidity and organ damage. Capable of affecting nearly any organ system or anatomic site, and showing considerable overlap in clinical presentation with various other diseases, IgG4-related disease often poses a diagnostic challenge for clinicians. Furthermore, there are no diagnostic biomarkers with high specificity for IgG4-related disease, and histopathological examination is nuanced and requires clinical correlation for accurate diagnosis. Therefore, it is crucial for clinicians to recognise the clinical phenotypes of IgG4-related disease. The disease is generally considered to have predominantly fibrotic and proliferative (or inflammatory) manifestations, with distinct clinical, serological and histopathological findings associated with each manifestation. However, the fibrotic and proliferative manifestations of this disease frequently occur together, thereby blurring this dichotomous distinction. In this Series paper, we provide a detailed overview of the clinical manifestations typical of the proliferative features of IgG4-related disease, with an emphasis on the diagnostic evaluation and differential diagnosis of each proliferative disease manifestation. In addition, we summarise the immune mechanisms underlying IgG4-related disease, suggest a framework for how to approach management and monitoring after the diagnosis is established, and highlight current unmet needs for patient care surrounding this disease.

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).

Renal tubular estrogen ß receptors are expressed at high levels in small vessel vasculitis and are primarily localized in the distal tubule

This study investigated the possible roles of renal estrogen receptors (ER) in glomerulonephritis associated with small vessel vasculitis. The relationships of ERs were investigated in antineutrophilic cytoplasmic antibody (ANCA)-associated glomerulonephritis and immunoglobulin A (IgA) nephropathy groups, which are small vessel vasculitis subtypes with two different glomerulonephritis development pathophysiologies. The design of this study was prepared as a retrospective cohort study. The study included 42 patients with ANCA-associated vasculitis and 18 with IgA nephropathy in the small vessel vasculitis group. For the control group, intact renal tissues of 28 patients who underwent nephrectomy due to renal cell carcinoma were used. Renal biopsy samples of the groups were stained with ER beta (ß) and ER alpha (α). Tubular ER ß expression score (TERßES) median values were found to be significantly higher in ANCA- associated vasculitis (B = 0.724, OR [95%CI]: 2.064 [1.141-3.731], p = .016) and IgA nephropathy (B = 0.898, OR [95%CI]: 2.454 [1.307-4.609], p = .005) than in intact kidney tissue. It was determined that tubular ERß was most frequently localized in the distal tubule at 57.9% and the second most common in the proximal tubule at 20.4%. The expression of tubular ERß is increased in glomerulonephritis due to small vessel vasculitis. Tubular ERßs are most commonly localized in the distal tubule. Further studies are needed to understand the physiological and pathophysiological effects of altered renal ER levels in small vessel vasculitis.

Antineutrophil cytoplasmic antibody-associated vasculitis predominantly manifesting tubulointerstitial nephritis: A case report

The common histopathology of antineutrophil cytoplasmic antibody-associated vasculitis comprises pauci-immune crescentic glomerulonephritis with concomitant tubulointerstitial nephritis. Tubulointerstitial nephritis in the absence of glomerular involvement in patients with antineutrophil cytoplasmic antibody-associated vasculitis is uncommon. We report a case of antineutrophil cytoplasmic antibody-associated vasculitis-associated acute kidney injury manifesting as tubulointerstitial nephritis without glomerulonephritis. A 75-year-old woman with fever, cough, and myalgia developed kidney dysfunction with inflammatory reactions and tubular-type proteinuria, without glomerular hematuria. A kidney biopsy revealed tubulointerstitial nephritis with arteritis. We ruled out important underlying etiologies of tubulointerstitial nephritis, including infection, drug reactions, and autoimmune diseases. Since chest high-resolution computed tomography demonstrated mild interstitial pneumonia in bilateral lower lung fields, myeloperoxidase antineutrophil cytoplasmic antibody was measured and found to be positive. Therefore, we diagnosed the patient with antineutrophil cytoplasmic antibody-associated vasculitis-associated tubulointerstitial nephritis but not glomerulonephritis, and interstitial pneumonia. The patient's kidney function and symptoms markedly improved with prednisolone treatment. Clinicians should maintain high-level vigilance for antineutrophil cytoplasmic antibody-associated vasculitis as a possible underlying component of tubulointerstitial nephritis, particularly when kidney function deteriorates with tubulointerstitial injuries without glomerular features.