Roles of IgG4 and IgG4/IgG ratio to IgG4-related disease in patients with elevated serum IgG4 level

Diagnostic accuracy of IgG 4/IgG and IgG 4 in patients with IgG 4-related disease: a meta-analysis

OBJECTIVE

This study aimed to evaluate and compare the diagnostic performance of immunoglobulin G4/Immunoglobulin G (IgG 4/IgG) and immunoglobulin G4 (IgG 4) alone in identifying immunoglobulin G4-related disease (IgG 4-RD).

METHODS

A systematic review and meta-analysis were conducted using data from Medline, Embase, and the Cochrane Library from inception to November 2024. Two meta-analyses were performed to assess the diagnostic accuracies of IgG 4/IgG and IgG 4 in IgG 4-RD patients.

RESULTS

Eight studies encompassing 754 IgG 4-RD patients and 9496 non-IgG 4-RD controls were included in the analysis. IgG 4/IgG demonstrated a sensitivity of 89% and a specificity of 91.6%, accurately detecting IgG 4-RD in 89% of cases and correctly identifying non-IgG 4-RD in 91.6% of cases. IgG 4 alone exhibited a higher sensitivity (94.9%) and a similar specificity (91%), indicating a slightly improved ability to identify IgG 4-RD cases. The positive likelihood ratio (PLR) and the negative likelihood ratio (NLR) for IgG 4/IgG were 7580 and 0.132, respectively, while IgG 4 alone had a PLR of 6403 and a lower NLR of 0.066, confirming the high diagnostic reliability. The diagnostic odds ratio (DOR) was 62.97 for IgG 4/IgG compared to 105.6 for IgG 4 alone, reflecting enhanced accuracy. The area under the curve (AUC) was 0.949 for IgG 4/IgG and 0.986 for IgG 4. The Q* index was 0.889 for IgG 4/IgG and 0.949 for IgG 4, further underscoring the diagnostic effectiveness of IgG 4 alone.

CONCLUSION

Both IgG 4/IgG and IgG 4 are highly accurate markers for diagnosing IgG 4-RD, with IgG 4 alone showing marginally higher sensitivity, DOR, and AUC. This suggests that IgG 4 alone may offer a slight advantage as a diagnostic marker for IgG 4-RD.

Diagnostic challenges of the idiopathic plasmacytic lymphadenopathy (IPL) subtype of idiopathic multicentric Castleman disease (iMCD): Factors to differentiate from IgG4-related disease

AIMS AND METHODS

Idiopathic multicentric Castleman disease (iMCD) is currently considered to be classified into three clinical subtypes, including idiopathic plasmacytic lymphadenopathy (IPL), thrombocytopaenia, anasarca, fever, reticulin fibrosis/renal dysfunction, organomegaly (TAFRO) and not otherwise specified (NOS). Among the three, iMCD-IPL closely mimics IgG4-related disease (IgG4-RD). In diagnosing IgG4-RD, it is sometimes challenging to distinguish iMCD-IPL patients that also meet the histological diagnostic criteria for IgG4-RD. In this study, we focused on the number of IgG4-positive cells in the lymph nodes and analysed the relationship with laboratory findings to distinguish iMCD-IPL from IgG4-RD. Thirty-nine patients with iMCD-IPL and 22 patients with IgG4-RD were included.

RESULTS

Among the cases considered to be iMCD-IPL, 33.3% (13/39) cases also met the histological diagnostic criteria for IgG4-RD and serum IgG4 levels were not different between the two groups. However, the serum IgG4/IgG ratio was significantly higher in IgG4-RD, with a cut-off value of 19.0%. Additionally, a significant positive correlation between serum IgG levels and the number of IgG4-positive cells was observed in iMCD-IPL (p=0.001). The serum IgG cut-off value for distinguishing iMCD-IPL meeting histological criteria for IgG4-RD from other iMCD-IPL was 5381 mg/dL.

CONCLUSIONS

iMCD-IPL cases with high serum IgG levels (>5000 mg/dL) were likely to meet the diagnostic criteria for IgG4-RD because of the numerous IgG4-positive cells observed. A combination of clinical presentations, laboratory values including the serum IgG4/IgG ratios and histological analysis is crucial for diagnosis of IgG4-RD and iMCD-IPL.

Therapeutic Uses of Rituximab and Clinical Features in Immunoglobulin G4-Related Disease: A Systematic Review

This research presents a systematic review focusing on rituximab's therapeutic applications in immunoglobulin G4 (IgG4)-related disease (IgG4-RD), a rare condition characterized by immune-mediated systemic inflammation and tissue fibrosis, as well as the clinical features of IgG4-RD. While the disease commonly affects organs such as the bile ducts, lymph nodes, retroperitoneum, pancreas, and salivary glands, it can potentially involve other organs. This intricacy often leads to diagnostic challenges due to clinical overlaps with cancer, infections, and other autoimmune disorders. The diagnosis of IgG4-RD necessitates a comprehensive approach involving laboratory tests, imaging studies, and clinical assessments. Symptoms can vary, ranging from lymphadenopathy to jaundice, affecting multiple organs. Although elevated blood IgG4 levels and findings of tissue involvement and fibrosis on imaging can be suggestive, they lack the specificity for a definitive diagnosis. Early diagnosis is crucial for initiating corticosteroids and immunosuppressive to prevent further damage from IgG4-RD. This study highlights the therapeutic role of rituximab in managing this condition. Adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria, the research identifies and evaluates relevant literature across various electronic databases, including PubMed, ScienceDirect, and Google Scholar. This review includes 14 selected publications, comprising three systematic reviews, three observational studies, four narrative reviews, and four case reports. The study design ensures a comprehensive evaluation of rituximab's potential efficacy in treating IgG4-RD and its associated clinical characteristics. Based on this study, it can be concluded that IgG4-RD can potentially be treated with rituximab, particularly in cases of relapse and maintaining remission.