Evaluation of diagnostic criteria for IgG4-related tubulointerstitial nephritis

[IgG4-related disease: Diagnostic criteria evolution toward the 2019 ACR/EULAR classification criteria]

The concept of IgG4-related disease (IgG4-RD) has recently been individualized in the early 2000s, but most of the organ involvements are known since more than 100 years. IgG4-RD is a non-malignant fibroinflammatory disorder, characterized by peculiar immunological and pathological abnormalities, which can affect virtually all organs or tissues. Diagnostic criteria have been proposed and have evolved rapidly, with general or organ specific criteria. An international and multidisciplinary group assembled by the American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR) has recently developed and validated a set of classification criteria called 2019 ACR/EULAR classification criteria for IgG4-related disease. The objective of this review is to discuss the evolution from organ specific and general diagnostic criteria toward the 2019 ACR/EULAR classification criteria, as well as respective benefits and limits of these criteria. The use of the 2019 ACR/EULAR classification criteria will help to better define homogeneous group of IgG4-RD patients in future clinical, epidemiological and basic science research studies on the disease.

Distribution characteristics of elevated serum immunoglobulin G4 (IgG4) and its relationship with IgG4-related disease

Objective: To elucidate the distribution characteristics of elevated serum immunoglobulin G₄ (IgG₄) and its relationship with immunoglobulin G₄-related disease (IgG₄-RD).Methods: In total, 14 522 unique patients who were tested for serum IgG₄ over a 4.5 year period were enrolled. Demographic and serological characteristics of all patients, and the range of diseases and serological characteristics of patients with elevated serum IgG₄, were retrospectively analysed. Organ involvement in IgG₄-RD patients and the utility of serum immunoglobulin for distinguishing IgG₄-RD from non-IgG₄-RD were also investigated.Results: Elevated serum IgG₄ (> 1.4 g/L) was observed in 1793/14 522 patients (12.3%) and primarily appeared in middle-aged and elderly men. Only 7.3% of patients with elevated serum IgG₄ met the diagnostic criteria for IgG₄-RD. Elevated serum IgG₄ was also found in over 30 types of non-IgG₄-RD. Serum IgG₄ levels were higher in IgG₄-RD patients with multiple-organ involvement and were positively correlated with the number of affected organs. The diagnostic utility of serum IgG₄ for IgG₄-RD was higher than that of the IgG₄/IgG ratio and serum IgG. The optimal serum IgG₄ cut-off value for diagnosing IgG₄-RD was 2.06 g/L, with a sensitivity of 95.6% and specificity of 94.7%.Conclusions: Elevated serum IgG₄ may be present in multiple non-IgG₄-RD conditions. However, a high serum IgG₄ concentration is of great value for IgG₄-RD diagnosis, and there appears to be a positive relationship between serum IgG₄ levels and organ involvement in patients with IgG₄-RD. Examining the IgG₄/IgG ratio and serum IgG does not improve the ability of IgG₄-RD diagnosis.

Acute tubulointerstitial nephritis and polyclonal hypergammaglobulinaemia: Which is the culprit?

Proton pump inhibitors (PPIs) are among the most frequent implicated drugs in acute tubulointerstitial nephritis (ATIN), nevertheless it is important to report cases with atypical profiles. A 80-year-old female, exposed during 34 months to omeprazole, presented with polyclonal hypergammaglobulinaemia and renal failure. After stopping omeprazole there was a partial improvement in serum creatinine and IgG. Renal biopsy revealed ATIN; immunohistochemistry for IgG4 was negative. Treatment with steroids and mycophenolate sodium improved renal function and normalized immunoglobulins. The lack of data of other entities and the patient’s evolution strongly point omeprazole as the culprit. After 27 months of follow-up, she remains clinical and analytically stable. ATIN caused by PPIs may appear after a long period of exposure and may be accompanied by analytical anomalies that simulate a systemic disease.