Description of patients with IgG4-related disease from a Hungarian centre

Clinical utility of serum IgG4 measurement

This article will review the structure and function of IgG4, methods of measuring serum IgG4 concentrations, clinical conditions associated with increased and decreased serum IgG4, and the test characteristics of serum IgG4 in the diagnosis and management of Immunoglobulin G4-Related Disease (IgG4-RD). The four subclasses of IgG were discovered in 1964 through experiments on monoclonal IgG in patients with myeloma. Since 2001, interest in measuring serum IgG subclasses has increased dramatically due to the emergence of IgG4-RD, a multisystem fibroinflammatory condition wherein polyclonal serum IgG4 concentration is increased in approximately 70% of cases. Increased serum IgG4 typically manifests as a restriction in the anodal gamma region on serum protein electrophoresis, often with beta-gamma bridging, and can be mistaken as a monoclonal protein or polyclonal increase in IgA. Limitations of current clinical methods used in quantitation of serum IgG4 concentrations will be discussed, including the common immunonephelometric assays and LC-MS/MS based assays. Polyclonal IgG4 elevation is not specific for IgG4-RD, and may also occur in conditions such as eosinophilic granulomatosis with polyangiitis (EGPA), lymphoma, and multicentric Castleman disease (MCD). Race and gender differences also affect interpretation of serum IgG4 concentrations, for instance Asians have a higher serum IgG4 concentration than Whites and males have a higher concentration than females.

Diagnostic performance of serum IgG4 level for IgG4-related disease: a meta-analysis

An elevated serum IgG4 level is one of the most useful factors in the diagnosis of IgG4-related disease (IgG4-RD). In this study, we performed a meta-analysis of the published articles assessing the diagnostic accuracy of serum IgG4 concentrations for IgG4-RD. The databases of MEDLINE/PubMed, EMBASE and Web of Science were systematically searched for relevant studies. Sensitivities and specificities of serum IgG4 in each study were calculated, and the hierarchical summary receiver operating characteristic (HSROC) model with a random effects model were employed to obtain the individual and pooled estimates of sensitivities and specificities. In total, twenty-three studies comprising 6048 patients with IgG4-RD were included in the meta-analysis. The pooled sensitivity was 85% with a 95% confidence interval (CI) of 78-90%; the pooled specificity was 93% with a 95% CI of 90-95%. The HSROC curve for quantitative serum IgG4 lies closer to the upper left corner of the plot, and the area under the curve (AUC) was 0.95 (95% CI 0.93, 0.97), which suggested a high diagnostic accuracy of serum IgG4 for the entity of IgG4-RD. Our study suggests that serum IgG4 has high sensitivity and specificity in the diagnosis of IgG4-RD.

Characterization and Comparison of Patient Subgroups Suspicious for IgG4-Related Disease and Malignant Lymphoma in Patients Followed-up for Sjögren's Syndrome

Differential diagnosis of patients with Sjögren's syndrome (SS), IgG4-related disease (IgG4-RD) and SS patients having high risk for lymphoma (LHR) can be challenging. Some patients with IgG4-RD might be misdiagnosed as having SS. There are special symptoms of SS that raise the possibility of IgG4-RD whereas other symptoms identify patients as having LHR. The purpose of this study was to characterize and compare patients with SS, possible IgG4-RD and SS patients with LHR. Sixty-five SS patients were divided into 4 subgroups according to having possible IgG4-RD (n = 15), LHR (n = 16), eligible for both aforementioned groups (n = 20) and not eligible for either group (n = 14), respectively. Four patients fulfilled the diagnostic criteria for IgG4-RD. The serum levels of IgG4 were significantly higher in patients suspicious for IgG4-RD compared to that of LHR patients (0.46 g/l vs. 0.12 g/l, p = 0.032). Shared features of the patient groups (salivary gland swelling (SGS) and lymphadenopathy), were separately analysed: SGS patients had higher IgG4/IgG ratio (p = 0.036), lymphadenopathic patients had higher IgG4 levels (p = 0.042). Some patients may be "hidden" under the diagnosis of SS. Although patients with LHR and patients with possible IgG4-RD share some symptoms, they differ significantly regarding IgG4 levels and IgG4/IgG ratio.