Diagnostic Performance of Serum IgG4 Levels in Patients With IgG4-Related Disease

Immunoglobulin G4 in primary Sjögren's syndrome and IgG4-related disease - connections and dissimilarities

Primary Sjögren's syndrome (pSS) is an autoimmune disease, with B cell hyperactivation and autoantibody production as its immunological hallmarks. Although the distinction between immunoglobulin G4-related disease (IgG4-RD) and pSS, based on the presence or absence of certain autoantibodies, seems easy to make, possibility of elevated serum IgG4 concentration and often similar organ involvement may lead to a misdiagnosis. The increased serum concentration of IgG4 in IgG4-RD is not clearly linked to the pathogenesis of IgG-RD and it has been suggested that it may constitute just an epiphenomenon. The aim of this article is to discuss the presence of IgG4 in pSS and IgG4-RD and its potential significance for these two diseases.

Factors related to elevated serum immunoglobulin G4 (IgG4) levels in a Japanese general population

BACKGROUND

Elevated serum immunoglobulin G4 (IgG4) concentrations are one of the characteristic findings in IgG4-related disease (IgG4-RD). This study investigated the frequency of elevated serum IgG4 levels and associated factors in a general Japanese population.

METHODS

Serum IgG4 concentrations were measured in 1,201 residents of Ishikawa prefecture who underwent general medical examinations. Factors associated with elevated serum IgG4 concentrations were assessed by logistic regression analysis. Participants with elevated serum IgG4 were subjected to secondary examinations.

RESULTS

The mean serum IgG4 concentration was 44 mg/dL, with 42 (3.5%) participants having elevated serum IgG4 levels. Age- and sex-adjusted logistic regression analyses showed that male sex, older age, and lower intake of lipids and polyunsaturated fatty acids and higher intake of carbohydrates in daily diet were associated with elevated serum IgG4 concentration. Subgroup analyses in men showed that older age, lower estimated glomerular filtration rates based on serum cystatin C (eGFR-cysC) levels, and higher hemoglobin A1c (HbA1c) levels were associated with elevated serum IgG4 concentration. Analyses in women showed that lower intake of lipids and fatty acids and higher intake of carbohydrates were significantly associated with elevated serum IgG4 concentration. One of the 15 participants who underwent secondary examinations was diagnosed with possible IgG4-related retroperitoneal fibrosis.

CONCLUSIONS

Elevated serum IgG4 levels in a Japanese general population were significantly associated with older age, male gender, and dietary intake of nutrients, with some of these factors identical to the epidemiological features of IgG4-RD.

Is systemic lupus erythematosus linked to Immunoglobulin G4 Autoantibodies?

Systemic lupus erythematosus (SLE) is a systemic autoimmune disorder characterized by a hyperactive immune system with multiple abnormalities in B-cell proliferation, antibody production, T-cell regulation, and immune complex (IC) formation. In humans, Immunoglobulin (Ig) G is found in four subclasses. IgG1-IgG4, which are distinguished by both structural and biological differences. Fab-arm Exchange (FAE), specific biases in the IgG4 response repertoire, and a decreased capacity to induce effector functions mediated by interactions in the fragment crystallizable (Fc) region are just a few of the distinctive characteristics of IgG4. The recent finding of the presence of double-stranded DNA (dsDNA) and antinuclear antibody (ANA)-IgG4 has raised attention to this IgG subclass and its possible role in SLE. IgG4 was previously believed to just have anti-inflammatory effects by inhibiting immune responses, but recent studies have shown that these antibodies can also play a role in the onset and development of some clinical disorders. To consider the clinical effects of IgG4 presence, it is necessary to discuss its characteristics, which could underlie the potential role it can play in SLE. Therefore, this study aimed to comprehensively review the role of IgG4 in SLE to elucidate the collective incidence of high IgG4 levels reported in some SLE patients.

Current and future advances in practice: IgG4-related disease

IgG4-related disease (IgG4-RD) is an increasingly recognized cause of fibroinflammatory lesions in patients of diverse racial and ethnic backgrounds and is associated with an increased risk of death. The aetiology of IgG4-RD is incompletely understood, but evidence to date suggests that B and T cells are important players in pathogenesis, both of which are key targets of ongoing drug development programmes. The diagnosis of IgG4-RD requires clinicopathological correlation because there is no highly specific or sensitive test. Glucocorticoids are highly effective, but their use is limited by toxicity, highlighting the need for studies investigating the efficacy of glucocorticoid-sparing agents. B cell-targeted therapies, particularly rituximab, have demonstrated benefit, but no randomized clinical trials have evaluated their efficacy. If untreated or under-treated, IgG4-RD can cause irreversible organ damage, hence close monitoring and consideration for long-term immunosuppression is warranted in certain cases.

Navigating the Spectrum: Atypical Pulmonary Involvement in Immunoglobulin G4-Related Disease

Immunoglobulin G4-related disease (IgG4-RD) is a systemic condition known to affect multiple organ systems. While its manifestations are diverse, pulmonary involvement, especially of the pleura, remains less common. We report the case of a 99-year-old Saudi male with a medical history of diabetes mellitus, chronic kidney disease, and hypertension. He presented with dyspnea and syncope, with radiological findings revealing pleural effusion and a mass in the right hemidiaphragm. Laboratory investigations highlighted elevated serum IgG4 levels, and histopathological evaluation confirmed the diagnosis of IgG4-RD. Notably, the patient's thoracic histopathology differed from typical IgG4-RD presentations, emphasizing the variability of the disease. This case underscores the significance of recognizing IgG4-RD as a potential cause of unexplained pleural effusion. It also highlights the need for a comprehensive diagnostic approach, integrating laboratory values, histopathological findings, and clinical context. Given the potential variability in thoracic IgG4-RD histopathology, clinicians should maintain a heightened awareness of this condition to avoid missed diagnoses.

Immunoglobulin G4-Related Lesions in Autoimmune Diseases: Unusual Presentations at Atypical Sites-A Tale of 2 Cases with Literature Review

Immunoglobulin G4-related disease (IgG4-RD) coexisting with clinically apparent autoimmune diseases, such as rheumatoid arthritis (RA) or antiphospholipid syndrome (APS), is a rarely documented combination in the scientific literature. In this case-based review, we present 2 intriguing cases with preexisting autoimmune diseases, namely, RA and primary APS, who exhibited coexistent IgG4- related lesions at unusual sites. The first case pertains to a patient with known RA who presented with an encasing mass in the esophagus leading to stricture, with histopathological diagnosis of IgG4-RD.The second patient, diagnosed with primary APS, experienced breathlessness, and imaging revealed a right atrial mass. Histopathological examination of the mass confirmed IgG4-RD. Notably, both patients demonstrated significant clinical improvement upon initiation of steroid therapy. Rheumatoid arthritis patients commonly exhibit elevated levels of IgG4 in their sera; however, RA with coexisting IgG4-RD is rarely reported in the literature. Similarly, APS with IgG4-related lesions is exceedingly rare. Although there are few case reports and series on esophageal and cardiac IgG4-RD, the occurrence of such unusual location of IgG4-related lesions in the context of known autoimmunity is presented here for the first time.

Clinical characteristics and outcome of autoimmune pancreatitis based on serum immunoglobulin G4 level: A single-center, retrospective cohort study

BACKGROUND

Autoimmune pancreatitis (AIP) has been linked with elevated immunoglobulin (Ig) G4 levels. The characteristics and outcomes of AIP based on serum markers have not been fully evaluated.

AIM

To compare clinical features, treatment efficacy, and outcome of AIP based on serum IgG4 levels and analyze predictors of relapse.

METHODS

A total of 213 patients with AIP were consecutively reviewed in our hospital from 2006 to 2021. According to the serum IgG4 level, all patients were divided into two groups, the abnormal group (n = 148) with a high level of IgG4 [> 2 × upper limit of normal (ULN)] and the normal group (n = 65). The t-test or Mann-Whitney U test was used to compare continuous variables. Categorical parameters were compared by the χ2 test or Fisher's exact test. Kaplan-Meier curves and log-rank tests were established to assess the cumulative relapse rates. Univariate and multivariate analyses were used to investigate potential risk factors of AIP relapse.

RESULTS

Compared with the normal group, the abnormal group had a higher average male age (60.3 ± 10.4 vs 56.5 ± 12.9 years, P = 0.047); higher level of serum total protein (72.5 ± 7.9 g/L vs 67.2 ± 7.5 g/L, P < 0.001), IgG4 (1420.5 ± 1110.9 mg/dL vs 252.7 ± 106.6 mg/dL, P < 0.001), and IgE (635.6 ± 958.1 IU/mL vs 231.7 ± 352.5 IU/mL, P = 0.002); and a lower level of serum complement C3 (100.6 ± 36.2 mg/dL vs 119.0 ± 45.7 mg/dL, P = 0.050). In addition, a lower number of cases with abnormal pancreatic duct and pancreatic atrophy (23.6% vs 37.9%, P = 0.045; 1.6% vs 8.6%, P = 0.020, respectively) and a higher rate of relapse (17.6% vs 6.2%, P = 0.030) were seen in the abnormal group. Multivariate analyses revealed that serum IgG4 [(> 2 × ULN), hazard ratio (HR): 3.583; 95% confidence interval (CI): 1.218-10.545; P = 0.020] and IgA (> 1 × ULN; HR: 5.908; 95%CI: 1.199-29.120; P = 0.029) and age > 55 years (HR: 2.383; 95%CI: 1.056-5.378; P = 0.036) were independent risk factors of relapse.

CONCLUSION

AIP patients with high IgG4 levels have clinical features including a more active immune system and higher relapse rate. Several factors, such as IgG4 and IgA, are associated with relapse.

[AL amyloidosis mimicking IgG4-related disease: case report]

The article describes a unique clinical case of AL amyloidosis mimicking IgG4-related disease. Plasma cell dyscrasias can mimic clinical and laboratory manifestations of rheumatic diseases, which can lead to a delay in diagnosis and inappropriate therapy.

A case of IgG4-related interstitial nephritis with ureteral obstruction: case report and literature review

BACKGROUND

IgG4-related disease (IgG4-RD) is a newly discovered systemic disease that can affect any organ or tissue in the body. IgG4-related kidney disease (IgG4-RKD) is relatively rare but essential to IgG4-RD. However, there are few reports of IgG4-RD mimicking malignant ureteral tumors leading to hydronephrosis. We report here a rare case of IgG4-RD involving the ureter.

CASE PRESENTATION

An 87-year-old man presented to our nephrology department with anorexia, nausea, and acute kidney injury in November 2020. Urinary computed tomography (CT) examination revealed a right lower ureter mass with right renal and ureter hydronephrosis. The serum level of IgG4 was 1890 mg/dL, and the concurrently renal biopsy revealed extensive infiltration of IgG4-positive plasma cells in renal interstitium, which was diagnosed as IgG4-associated tubule-interstitial nephritis(IgG4-TIN). The renal function improved significantly after double-J tube implantation of the right ureter and moderate-dose hormone therapy. The serum IgG4 decreased to the normal range, and the right lower ureter mass almost disappeared after one year of low-dose hormone maintenance therapy.

CONCLUSION

IgG4-RD can present as a mass in the renal pelvis and (or) ureter, leading to hydronephrosis. Therefore, early recognition of this disease is significant. Most patients respond well to hormonal therapy to avoid surgical treatment due to misdiagnosis as malignant tumors, causing secondary harm to patients.

The Positive Predictive Value of a Very High Serum IgG4 Concentration for the Diagnosis of IgG4-Related Disease

OBJECTIVE

Serum IgG4 concentrations are used to evaluate a diagnosis of IgG4-related disease (IgG4-RD), but the positive predictive value (PPV) of a very high IgG4 level is uncertain. This study evaluated the PPV of a very high IgG4 concentration for diagnosing IgG4-RD.

METHODS

The data warehouses of 2 large academic healthcare systems were queried for IgG4 concentration test results. Cases with serum IgG4 concentrations > 5× the upper limit of normal (ULN) were included. Cases of IgG4-RD were determined using the American College of Rheumatology/European Alliance of Associations for Rheumatology (ACR/EULAR) classification criteria. The PPV for IgG4-RD of an IgG4 concentration > 5× ULN was estimated. Other conditions associated with very high IgG4 concentrations and specific features of IgG4-RD cases were characterized.

RESULTS

IgG4 concentrations were available in 32,206 cases. Of these, 3039 (9.4%) had elevated IgG4 concentrations, and a final cohort of 191 (0.6%) cases had IgG4 concentrations > 5× ULN (median age 66 yrs, 72% male). The PPV of an IgG4 concentration > 5× ULN for a diagnosis of IgG4-RD was 75.4% (95% CI 68.7-81.3). In the remaining cases, elevated IgG4 concentrations were observed among patients with malignancies, autoimmune diseases, and infections.

CONCLUSION

The majority of cases with serum IgG4 concentrations > 5× ULN in this study had IgG4-RD. These data support the high weight placed on very high serum IgG4 concentrations in the ACR/EULAR classification criteria. However, 25% of cases with very high IgG4 concentrations had an alternative diagnosis, underscoring the importance of considering the broad differential of etiologies associated with an elevated IgG4 concentration when evaluating a patient.

Diagnostic Utility of Serum IgG4 in Autoimmune Pancreatitis: An Updated Comprehensive Systematic Review and Meta-analysis

OBJECTIVES

Despite many studies suggesting an association between serum immunoglobulin G4 (sIgG4) and autoimmune pancreatitis (AIP), the evidence of utility in differentiation between AIP and pancreatic cancer (PC) remain uncertain.

METHODS

The analysis based on published studies. Data were pooled by means of a random-effects model, and sensitivity, specificity, diagnostic odds ratios (DOR), areas under summary receiver operating characteristic curves were calculated.

RESULTS

In the included thirteen studies, sIgG4 were measured in 594 patients with AIP and 958 patients with PC. The pooled sensitivity, specificity, DOR, and area under the curve were 0.72 [95% confidence interval (CI): 0.68-0.75], 0.93 (95% CI: 0.92-0.95), 51.37 (95% CI: 23.20-113.74), and 0.91 (95% CI: 0.87-0.95). Subgroup analyses of the DORs for region and year: Asia, (112.10; 95% CI: 27.72-453.32), non-Asia (26.01; 95% CI: 12.38-54.65), and year before 2011 (107.61; 95% CI: 39.30-294.68), year after 2011 (26.96; 95% CI: 9.78-74.32). Overall, sIgG4 was associated with AIP, the result revealed a moderate sensitivity 0.72 and high specificity 0.93. In the meta-analysis, the pooled DOR of sIgG4 levels of 2-fold upper limit 50.44 was similar with the DOR 51.37 when 1-fold cut-off value, but the summary receiver operating characteristic was 0.755 and 0.91. The higher specificity (from 93% to 98%) derived from the cut-off value (from 130-140 to 260-280 mg/dL) for sIgG4 occurred at a significant reduction in sensitivity (from 72% to 43%).

CONCLUSIONS

The study revealed sIgG4 is a good marker of AIP. Screening of sIgG4 may help clinicians differentiate between AIP and PC, and the best cut-off value should be 140 rather than 280 mg/dL.

A Unified Serum IgG4 Cutoff Level for the Diagnosis of IgG4-Related Disease Using a Wide Array of Kits

Objectives

An IgG4 level above 1350 mg/L is one of the comprehensive criteria for the diagnosis of IgG4-related disease (IgG4-RD). The purpose of this study was to evaluate the differences in IgG4 levels determined using reagents from two main manufacturers and their concordance with clinical diagnosis.

Methods

IgG4 levels were measured in 309 patients, including 146, 40, 42, 41, and 40 patients with untreated IgG4-RD, pancreatic cancer, primary Sjogren syndrome, systemic lupus erythematosus, and idiopathic retroperitoneal fibrosis, respectively, and 141 healthy controls. The results obtained using the Binding Site and Siemens reagents were compared in patients with IgG4-RD.

Results

The serum IgG4 level measured using the Siemens reagent was almost two times that measured using the Binding Site reagent. The rate of IgG4-negative patients, which was 19.9% based on measurement using the Binding Site reagent, was only 4.8% based on measurement using the Siemens reagent (P &lt; 0.001).

Conclusions

There were significant differences in serum IgG4 levels based on commonly used reagents from different manufacturers. The IgG4 cutoff level of 1350 mg/L was not suitable for all detection reagents. Clinicians and patients should be cognizant of these differences associated with the specific detection reagents when evaluating the test results.

Unique case of IgG4-related disease of the renal pelvis involving the inferior vena cava masquerading as locally advanced urothelial cancer

Immunoglobulin G4-related disease (IgG4-RD) is a systemic disease which can affect any organ or tissue in the body but most commonly affects the pancreas, biliary ducts, salivary glands, ocular system and lymph nodes; renal involvement is relatively uncommon and there are no previous reported cases of inferior vena cava involvement. Herein, a 48-year-old Asian man with an unremarkable medical history was found to have an obstructing right renal pelvis mass extending to and involving the inferior vena cava, highly suspicious for upper tract urothelial carcinoma that could not be ruled out based on ureteroscopy and urine cytology. Open radical nephroureterectomy with enbloc resection of a segment of the inferior vena cava and left renal vein ostium was performed, with reconstruction of the inferior vena cava and left renal vein with polytetrafluoroethylene grafts. Final histopathology confirmed the diagnosis of IgG4-related disease. This case demonstrates that IgG4-related disease can mimic upper tract urothelial cancer and should be considered as a diagnosis in atypical presentations of tumours of the upper urinary tract.

The Role of IgG4 in Autoimmunity and Rheumatic Diseases

The distinguishing of the IgG4-related disease (IgG4-RD) from among other rheumatic diseases has brought attention to the IgG4 subclass of immunoglobulins. It is the least numerous subclass among immunoglobulins G. In general, IgG4 is considered to be non-inflammatory and tolerance inducing, due to its unique structure. However, in IgG4-RD this antibody plays a pathogenic role in activation of the fibrinogenesis and of the inflammatory process; there are also suggestions that it may be a marker of an abnormal inflammatory response. The importance of IgG4 for the pathogenesis of allergic diseases, with a vital role of its ratio to immunoglobulin E (IgE/IgG4 ratio), has been known for years. The role of IgG4 in the course and pathogenesis of rheumatic diseases is still being researched and is not yet fully understood. Increased IgG4 levels have been revealed in rheumatoid arthritis, although no clear link between this phenomenon and disease activity has been demonstrated. There are articles on the potential importance of IgG4 concentration (of both elevated and decreased serum levels) in Sjogren’s syndrome. Additionally, anti-nuclear IgG4 antibody significant titers have been detected in SLE patients, and it has been suggested that the effect of these antibodies on complement consumption and the production of proinflammatory cytokines may play a role in inhibiting the progression of SLE. IgG4 plays a role in autoimmune diseases other than rheumatic diseases, such as pemphigus, bullous pemphigoid, idiopathic membranous glomerulonephritis, or myasthenia gravis, but also in helmints infections. Research shows the importance of IgG4 in malignancy of neoplasms. Melanoma cells are known to stimulate IgG4 production through a modified Th2-based inflammatory response. The role of this immunoglobulin in cholangiocarcinoma is also considered as possible. The aim of this review article is to discuss the current knowledge of IgG4 not only from the perspective of the IgG4-RD but also from a point of view of other autoimmune diseases with particular emphasis on rheumatic diseases.

Pleural Involvement in IgG4-Related Disease: Case Report and Review of the Literature

Diagnostic work-up of IgG4-related disease (IgG4-RD) pleural involvement is a complex task, as there is a broad spectrum of differential diagnoses to consider. We report the case of a patient presenting with relapsing pleural effusion, discussing the main challenges for achievement of a definite diagnosis. A 63-year-old man was admitted for pleural effusion prevalent on the ride side, initially labeled as idiopathic non-specific pleuritis, based on tissue evaluation after a medical thoracoscopy. He was started on steroids with initial improvement, but a later CT scan showed a relapse of pleural effusion associated with diffuse pleural thickening; a subsequent surgical pleural biopsy revealed features suggestive for IgG4-RD, with a marked increase of IgG4 positive plasma cells. High IgG4 serum levels were also found. The present case underlines the importance of increasing awareness of this potential condition among physicians in order to properly guide the diagnostic work-up, as it is likely that IgG4-RD accounts for a proportion of patients with pleural effusions, labeled as idiopathic. In particular, in patients with unexplained pleural effusion, IgG4-RD should be included among differential diagnoses when lymphoplasmacytic infiltration is observed, and a multidisciplinary interaction between clinicians and pathologists appears crucial for an accurate diagnosis and an appropriate management.

Curious case of the unexplained exudative pleural effusion

We report a case of a 74-year-old male patient who was referred to the respiratory clinic with an incidental finding of a left sided pleural effusion. He was initially being treated by the general practitioner for chest infection with productive cough that had limited resolution after course of oral antibiotics. At the pleural clinic, 1.5 L of serosanguineous fluid was drained and sent for diagnostics. However, the diagnosis only reached as far as idiopathic exudative effusion with lymphocytes and plasma cells. He was then referred for video-assisted thoracoscopic surgery pleural biopsy and pleurodesis. It revealed black pleura with abundant IgG4 positive cells. He is followed up in respiratory clinic where further discussion and treatment has commenced.

Cut-off values of serum IgG4 among three reagents, including a novel IgG4 reagent: a multicenter study

Elevated serum IgG4 is a useful marker of IgG4-related disease (IgG4-RD) activity. However, there is no uniformity in the cut-off values of IgG4 among the various reagents. The aim of this study was to compare the measured and cut-off values of IgG4 assessed using three different reagents. This study enrolled 466 IgG4-RD and non-IgG4-RD patients who required measurement of serum IgG4 levels to diagnose or treat IgG4-RD. Serum IgG4 was measured using three reagents: N-assay LA IgG4 Nittobo (Nittobo), BS-NIA IgG4 (TBS), and N Latex IgG4 (Siemens). The values obtained using the three reagents were compared, and cut-off values were calculated for each. Although there was good correlation among the results with the three reagents, the measured and cut-off values were all different. The Nittobo values were 1.4 times the TBS values and the TBS values were almost half those of the Siemens values. ROC curve analysis showed cut-off values for the Nittobo, TBS, and Siemens reagents of 1.42, 1.31, and 2.38 g/L, respectively. The measured and cut-off values of serum IgG4 vary depending on the reagents used for the assay, although there is good correlation among the values measured by the three reagents.

The 2020 revised comprehensive diagnostic (RCD) criteria for IgG4-RD

IgG4-related disease (IgG4-RD) is a fascinating clinical entity first reported in this century in Japan, and includes a wide variety of diseases, such as formerly named Mikulicz's disease (MD), autoimmune pancreatitis (AIP), interstitial nephritis, prostatitis and retroperitoneal fibrosis. The Japanese IgG4 team organized by the Ministry of Health, Labor and Welfare (MHLW) of Japan has published the first criteria, comprehensive diagnostic (CD) criteria for IgG-RD 2011. Thereafter, IgG4-RD has been accepted widely and many cases have been reported from all over the world. Several problems have arisen in clinical practice, however, including the difficulty obtaining biopsy samples, and the sensitivity and specificity in cut off level of serum IgG4 and impaired immunostaining of IgG4. Given these situations, the Japanese IgG4 team has updated the 2011 comprehensive diagnostic criteria for IgG4-RD and propose the 2020 revised comprehensive diagnostic (RCD) criteria for IgG4-RD, which consists of 3 domains; 1) Clinical and radiological features, 2) Serological diagnosis and 3) Pathological diagnosis. In addition, the new pathological diagnosis is composed by three sub-items including storiform fibrosis and obliterative phlebitis.

Advances in the diagnosis and management of IgG4 related disease

IgG4 related disease was recognized as a unified disease entity only 15 years ago. Awareness of IgG4 related disease has increased worldwide since then, and specialists are now familiar with most of its clinical manifestations. Involvement of the pancreato-biliary tract, retroperitoneum/aorta, head and neck, and salivary glands are the most frequently observed disease phenotypes, differing in epidemiological features, serological findings, and prognostic outcomes. In view of this multifaceted presentation, IgG4 related disease represents a great mimicker of many neoplastic, inflammatory, and infectious conditions. Histopathology remains key to diagnosis because reliable biomarkers are lacking. Recently released classification criteria will be invaluable in improving early recognition of the disease. IgG4 related disease is highly treatable and responds promptly to glucocorticoids, but it can lead to end stage organ failure and even death if unrecognized. Prolonged courses of corticosteroids are often needed to maintain remission because the disease relapses in most patients. Rapid advancement in our understanding of the pathophysiology of IgG4 related disease is leading to the identification of novel therapeutic targets and possible personalized approaches to treatment.

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.

Immunoglobulin G4-Related Disease of the Ovary Mimicking Bilateral Ovarian Malignancies

Immunoglobulin G4-related disease (IgG4-RD) is a fibro-inflammatory condition characterized by several pathological features that can theoretically involve all organs. Ovarian involvement in IgG4-RD has been reported by two studies only. Herein, we report a pathologically confirmed case of ovarian involvement of IgG4-RD, which mimicked bilateral ovarian malignancies on computed tomography and magnetic resonance imaging.

IgG4-type Multiple Myeloma with Diffuse Enlargement of the Thyroid Requiring Differentiation from IgG4-related Disease

We herein report a 65-year-old man with elevated serum IgG4 levels, enlarged thyroid, and renal dysfunction, mimicking IgG4-related disease (IgG4-RD). The definitive diagnosis of IgG4-RD was not established because a tissue biopsy revealed no IgG4-positive cell infiltration or fibrosis. The presence of an M peak in the β fraction, Bence Jones protein in urine, and progressive anemia suggested multiple myeloma (MM). The κ/λ ratio was >100, tumor plasma cells were present at >20% in bone marrow, and immunostaining revealed IgG4-positive plasma cells; therefore, he was diagnosed with IgG4-type MM. Patients with elevated IgG4 levels with no significant mass lesions should undergo systemic examinations to exclude malignancy.

Consideration concerning similarities and differences between ANCA-associated vasculitis and IgG-4-related diseases: case series and review of literature

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) and immunoglobulin G4-related diseases (IgG4-RD) are regarded as entirely different disease types with different etiological mechanisms. However, we experienced two cases that had clinical features of both AAV and IgG4-RD. The first case is an 81-year-old woman who showed periaortitis and retroperitoneal fibrosis and periarteritis with elevation of myeloperoxidase-anti-neutrophil cytoplasmic antibody and IgG4 levels. The second case is a 63-year-old woman who had dura mater, ear, nose, lung, and kidney involvement with serum negative for ANCA and elevated IgG4. Renal biopsy revealed tubulointerstitial nephritis involving IgG4⁺ plasma cells (IgG4⁺/IgG⁺ cell ratio of ≥ 40%). On the other hand, lung biopsy showed features of granulomatosis with polyangiitis (GPA). These two cases suggested that AAV and IgG4-RD might overlap. To investigate the similarities and differences between AAV and IgG4-RD, we retrospectively analyzed 13 cases of typical GPA, a subtype of AAV, and 13 cases of typical IgG4-RD at our hospital for comparison of clinical features and found some differences that can be useful in the differential diagnosis between the two diseases. Although AAV and IgG4-RD are distinguishable based on characteristic findings in many cases, the diagnosis can be unclear in rare cases, in which clinicians should consider possible coexistence of AAV and IgG4-RD when performing further workup. Here, we discuss the similarities and differences between AAV and IgG4-RD on the basis of our results and past literature.

Immunoglobulin G4-Related Mastitis: An Unusual Case of Recurrent Breast Abscess

Immunoglobulin G4-related mastitis (IgG4-RM) is an uncommon entity in clinical practice which has an evolving spectrum of manifestations and presently is of high clinical interest among rheumatologists. Since its closest differential remains breast carcinoma, the importance of describing this entity is in the fact that early diagnosis, awareness and timely management can save the patient from unnecessary surgical intervention and its complications. Tumefactive lesions are considered hallmark of this disease, but rarely abscess may also be the presenting feature. In this article, we describe a 24-year-old female patient of a very unusual case of IgG4-RM presenting as recurrent breast abscess, its successful management and discussion about novel treatment strategies.

Evaluation of a novel serum IgG4 assay and determination of reference interval for the Japanese population

BACKGROUND

IgG4-related disease (IgG4-RD) is a new syndrome characterized by elevated serum IgG4 concentration and tissue infiltration of IgG4-positive plasma cells. Here, we evaluated the analytical performance of a new IgG4 assay reagent featuring a wide dynamic range, highly specific monoclonal antibody, and the reversed passive latex agglutination assay and determined the IgG4 reference interval (RI) for the Japanese population.

METHODS

Performance evaluations were conducted on precision, linearity, sensitivity, interference, and method comparison with The Binding Site (TBS) and Siemens reagents. The RI was derived by the parametric method from 619 apparently healthy Japanese 18 to 65 years of age.

RESULTS

Between-day precisions ranged from 1.99 to 5.52 CV%. Linearity was confirmed up to 5.0 g/l. The limit of quantitation was 0.085 g/l. Interfering substances did not significantly influence values. Method comparison among the 3 reagents yielded correlation coefficients between 0.973 and 0.988. Values for the new reagent matched those of TBS reagent except at a higher concentration range, where reactivity dissociated. The RI was 0.11-1.21 g/l without distinction by sex and age.

CONCLUSION

The novel IgG4 assay reagent demonstrated satisfactory analytical performance for clinical use. Because of matched value with TBS reagent at low concentrations, it is possible to use the IgG4-RD cut-off value determined by TBS reagent.

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.

IgG4-Related Ophthalmic Disease Presenting as Meningitis and Panuveitis

Purpose. We report an uncommon case of immunoglobulin gamma 4-related ophthalmic disease (IgG4-ROD) presenting as meningitis and panuveitis. Observations. A 35-year-old male with no prior ophthalmic history presented with headaches, altered mental status, and fever of unknown origin. A lumbar puncture (LP) revealed an elevated white count with lymphocytic predominance, confirming a suspected meningitis. After an extensive work-up, he was discharged on oral acyclovir to cover for presumed aseptic meningitis. The patient initially improved, however, bilateral eye pain, redness, and photophobia 2 weeks after discharge prompted his first visit to the ophthalmology clinic. Exam at that time was consistent with bilateral anterior uveitis for which he was given topical prednisolone and cyclopentolate. In addition to the preceding work-up, quantitative immunoglobulin serology including IgG4 levels was added. At follow-up, he was found to have increased ocular inflammation with vitreitis, nerve head edema, and subclinical macular thickening. Visual acuity (VA) had decreased in both eyes. Serology titers for IgG had resulted in a significant elevation in IgG subclass 4 (IgG4). Optical coherence tomography (OCT) and fundus fluorescein angiography (FFA) confirmed posterior retinal involvement. The patient was diagnosed with presumed bilateral panuveitis secondary to IgG4-ROD. Conclusions and Importance. IgG4-RD can be a serious condition that requires careful consideration and intuition to diagnose. This report serves to encourage ophthalmologists to consider IgG4-ROD in cases of idiopathic systemic inflammation with ophthalmic involvement.

Biomarkers in IgG4-related disease: A systematic review

OBJECTIVE

ImmunoglobulinG4-related disease (IgG4-RD) is a recently recognized disease and, as such, there is a pressing need to identify biomarkers for diagnosis, monitoring disease activity, and predicting prognosis and response to therapy. Here, we review the recent development and identification of biomarkers for IgG4-RD.

METHODS

Through extensive literature review and analysis, we updated the biomarkers for IgG4-RD and further put forward our own viewpoints.

RESULTS

In addition to traditional biomarkers, such as serum IgG4 concentration and typical histological characteristics, several novel indicators, including IgG2, serum soluble IL-2 receptor (sIL2R), and cc-chemokine ligand 18 (CCL18), indicate inflammation and fibrosis and can be used to accurately diagnose and predict treatment response. Studies to identify target autoantigens in IgG4-RD have shed light on the unmet need for biomarkers that can identify this disorder. Additionally, both serological and histopathologic immune cells involved in antigen-induced responses, innate immune cells (macrophages, mast cells, and the I-IFN/ IL-33 pathway), as well as subsequent acquired immune cells (T and B cell subsets), may also serve as new biomarkers for IgG4-RD. Since IgG4-RD often clinically manifests with multiple organs involvement, non-invasive PET-CT can improve diagnosis and antidiastole levels.

CONCLUSION

These novel biomarkers provide information to help diagnose IgG4-RD, monitor disease activity, as well as predict prognosis and response to therapy.

New insights into the pathophysiology of IgG4-related disease and markers of disease activity

INTRODUCTION

Recently, IgG4-related disease (IgG4-RD) has become a well-recognized clinical entity, although its causes are still not well understood. The pathophysiology of IgG4-RD has been reported from a variety of aspects. Areas covered: In this review, we outline a number of recent advances in our understanding of the pathogenesis of IgG4-RD, divided according to acquired immunology and innate immunology and other topics. Furthermore, we also focus on some proposed markers of disease activity of IgG4-RD. Expert commentary: One striking advance made recently is the identification of novel autoantigens of IgG4-RD. At the onset of IgG4-RD, various T cell side factors such as Tfh, Th2 cells are at work, in addition to B cell side factors like plasmablasts and plasma cells, and innate immunology via TLR and M2 macrophages. The efficacy of B cell depletion therapy using rituximab has been reported, with the establishment of steroid-sparing therapies targeting other molecules also anticipated.

IgG4-related retroperitoneal fibrosis overlapping with primary biliary cirrhosis and primary Sjögren's syndrome: A case report

RATIONALE

IgG4-related disease (IgG4-RD) is a chronic fibro-inflammatory disorder which is characterized by elevated levels of serum IgG4 and infiltration of IgG4-bearing plasma cells in the involved organs. Primary biliary cirrhosis (PBC) and Primary Sjögren's syndrome (pSS) are both distinct from IgG4-related disease. We herein describe a Chinese patient with IgG4-related RPF overlapping with PBC and pSS.

PATIENT CONCERNS

We report a case of 69-year-old male with recurrent lower abdominal pain for 10 months. Laboratory data showed elevated erythrocyte sedimentation rate and hepatobiliary enzymes, renal dysfunction, high titers of antinuclear antibody, anti-SS-A antibody and anti-mitochondrial type 2, high immunoglobulin (Ig) G levels and elevated serum IgG4 (9 g/L). Contrast-enhanced computed tomography and magnetic resonance imaging were suggestive of retroperitoneal fibrosis and unilateral ureteral occlusion. Immunohistochemical staining for IgG4 did not demonstrate infiltration of IgG4-positive plasma cells in the retroperitoneal mass, but revealed significant infiltration of lymphocytoplasma cells as well as fibrosis and fibrin accumulation.

DIAGNOSES

The patient was diagnosed with IgG4-related retroperitoneal fibrosis based on the International Consensus Diagnostic Criteria. He was also diagnosed with primary biliary cirrhosis and primary Sjögren's syndrome.

INTERVENTIONS

250 mg ursodeoxycholic acid was administered twice daily, and prednisolone was initiated at a dose of 40 mg/day and then tapered to 25 mg after 45 days.

OUTCOMES

The size of the retroperitoneal soft tissue mass gradually reduced and the abnormal laboratory parameters were restored to normal.

LESSONS

This rare clinical condition has seldom been reported in the literature, which suggests that common immunogenetic factors may be involved in the development of IgG-related RPF, PBC and pSS.

IgG4-related disease involving polyserous effusions with elevated serum interleukin-6 levels: a case report and literature review

Immunoglobulin G4-related disease (IgG4-RD) is a recently described immune-mediated fibroinflammatory disease with a characteristic histopathologic appearance that can affect various organs. We report a 43-year-old Chinese female patient with IgG4-RD involving polyserous effusions with reports of worsening exertional dyspnea for 3 months. Laboratory blood tests revealed that serum interleukin (IL)-6, carbohydrate antigens (CA-199 and CA-125), and alpha-fetoprotein levels were significantly increased, but serum IgG4 levels were normal. Repeat pleural effusion and ascite analysis showed lymphocyte-predominant exudates. In addition, computed tomography scan showed massive pleural effusion in the right pleural cavity, abdominal effusion, and some pericardial effusion with a partial compression atelectasis. Further, medical thoracoscopy was performed to examine the pleural cavity and found multiple nodules on the pleura and partly thickened pleura with a reddish color. Histopathologic and immunohistochemical examination revealed marked lymphocytes and IgG4-positive plasma cell infiltration. The patient was finally diagnosed with IgG4-RD according to the comprehensive diagnostic criteria, although the patient presented similar serological and pathological manifestations of Castleman disease (CD). Our case suggests that IgG4-RD may be one of the causes of polyserous effusions and shows the difficulties in differentiating between IgG4-RD and CD.

Clinical Utility of FDG PET/CT in Patients with Autoimmune Pancreatitis: a Case-Control Study

Autoimmune pancreatitis (AIP) shares overlapping clinical features with pancreatic cancer (PC). Importantly, treatment of the two conditions is different. We investigated the clinical usefulness of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in patients with suspected AIP before treatment. From September 2008 to July 2016, 53 patients with suspected AIP at National Taiwan University Hospital had PET/CT prior to therapy to exclude malignancy and evaluate the extent of inflammation. Their scans were compared with those from 61 PC patients. PET imaging features were analyzed using logistic regression. Significant differences in pancreatic tumor uptake morphology, maximum standardized uptake value, high-order primary tumor texture feature (i.e. high-gray level zone emphasis value), and numbers and location of extrapancreatic foci were found between AIP and PC. Using the prediction model, the area under curve of receiver-operator curve was 0.95 (P < 0.0001) with sensitivity, specificity, positive predictive, and negative predictive values of 90.6%, 84.0%, 87.9%, and 87.5% respectively, in differentiating AIP from PC. FDG PET/CT offers high sensitivity, albeit slightly lower specificity in differentiating AIP from PC. Nonetheless, additional systemic inflammatory foci detected by the whole body PET/CT help confirm diagnosis of AIP in these patients before initiating steroid therapy, especially when biopsy is inconclusive.

Current approach to the diagnosis of IgG4-related disease - Combination of comprehensive diagnostic and organ-specific criteria

IgG4-related disease (IgG4-RD) is a fascinating clinical entity proposed by Japanese investigators, and includes a wide variety of diseases, formerly diagnosed as Mikulicz's disease (MD), autoimmune pancreatitis (AIP), interstitial nephritis, prostatitis, retroperitoneal fibrosis, etc. Although all clinicians in every field of medicine may encounter this new disease, a unifying diagnostic criterion has not been established. In 2011, the Japanese IgG4 team, organized by the Ministry of Health, Labor and Welfare (MHLW) of Japan, published comprehensive diagnostic criteria for IgG4-RD. Several problems with these criteria have arisen in clinical practice, however, including the difficulty obtaining biopsy samples from some patients, and the sensitivity and the specificity of techniques used to measure serum IgG4 concentrations. Although serum IgG4 concentration is an important clinical marker for IgG4-RD, its diagnostic utility in differentiating IgG4-RD from other diseases, called IgG4-RD mimickers, remains unclear. This review describes the current optimal approach for the diagnosis of IgG4-RD, based on both comprehensive and organ-specific diagnostic criteria, in patients with diseases such as IgG4-related pancreatitis (AIP), sclerosing cholangitis, and renal, lung and orbital diseases.

Diagnostic performances of serum IgG4 concentration and IgG4/IgG ratio in IgG4-related disease

Patients with IgG4-related disease (IgG4-RD) often have elevated serum IgG4 levels. Here, we aimed to evaluate the diagnostic performances of elevated serum IgG4 concentration and IgG4/IgG ratio for IgG4-RD. We retrospectively analyzed 1381 patients subjected to serum IgG subclass testing to differentiate IgG4-RD from other diseases at Peking University People's Hospital from 2012 to 2016. This sample included 133 IgG4-RD patients and 1248 non-IgG4-RD patients. Serum IgG subclass concentrations were measured using Siemens reagents. The median values (25th-75th percentile) for serum IgG4 concentration and IgG4/IgG ratio, respectively, were 8640 (3970-17750) mg/L and 0.339 (0.229-0.517) in IgG4-RD patients and 450 (220-920) mg/L and 0.032 (0.014-0.061) in non-IgG4-RD patients (p < 0.001). For distinguishing IgG4-RD from non-IgG4-RD, the optimal cut-off values of IgG4 and IgG4/IgG were 2100 mg/L and 0.114, respectively. The corresponding area under the curve (AUC) values were 0.964 and 0.970, respectively. Comparison of the receiver operating characteristic curves revealed a significant difference between these AUC values (p = 0.002). The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), respectively, were 94.7, 91.6, 54.5, and 99.4% for the IgG4 optimal cut-off value and 96.2, 92.1, 56.4, and 99.6% for the IgG4/IgG optimal cut-off value. Our results confirmed that elevated serum IgG4 concentration and IgG4/IgG ratio were of great value for IgG4-RD diagnosis.

IgG4-related disease involving vital organs diagnosed with lip biopsy: A case report and literature review

Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized new disease entity characterized by elevated serum IgG4 and infiltration of IgG4 plasma cells in affected tissues. Histological examination is essential for definitive diagnosis, as other pathological conditions can also present with serum IgG4 elevation. However, IgG4-RD frequently involves vital or internal organs that are difficult to perform biopsies. We herein report a unique case of IgG4-RD involving vital organs that could be successfully diagnosed by alternative lip biopsy, an accessible, little invasive procedure, despite no apparent manifestation demonstrating the involvement in labial salivary gland.A 60-year-old man with swelling of both submandibular glands and elevated serum creatinine level visited our hospital. His labial salivary glands appeared normal. His blood test showed high serum IgG4, and positron-emission computed tomography revealed abnormal uptake in submandibular glands, periaorta, and left kidney with hydronephrosis. We suspected him of IgG4-RD; however, the involved organs were difficult to approach for histological examination. Alternatively, we performed lip biopsy and proved massive infiltration of IgG4 plasma cells leading to the diagnosis with IgG4-RD. Treatment with prednisolone resulted in the remarkable improvement of organ involvements and the normalization of serum IgG4 level after 3 months. Prednisolone was gradually tapered without the relapse of disease.The early recognition and diagnosis of IgG4-RD is clinically important because delay in the treatment initiation leads to fibrosis with irreversible organ damage. Our case highlights the possibility that lip biopsy is a promising option for histological examination in patients with IgG4-RD in whom affected organs are difficult to access, leading to early diagnosis with appropriate treatment.

Diagnostic Value of Serum IgG4 for IgG4-Related Disease: A PRISMA-compliant Systematic Review and Meta-analysis

Many studies about serum IgG4 for the diagnosis of IgG4-related disease (IgG4-RD) have been reported. However, these studies had relatively small sample sizes and the diagnostic accuracy values varied much between them.The aim of this study was to perform a meta-analysis to evaluate the diagnostic value of serum IgG4 for IgG4-RD.We conducted a search of relevant articles using MEDLINE, EMBASE, Web of Science, SCOPUS, and Cochrane Library databases published before December 2015.Studies those assessed the diagnostic accuracy of serum IgG4 for IgG4-RD and those provided the cut-off value for serum IgG4 were included.Data were synthesized using the random-effect model. Statistical analysis was performed using STATA with the MIDAS module and Meta-DiSc 1.4 software.A total of 9 case-control studies were analyzed, which included 1235 patients with IgG4-RD and 5696 overall controls. The pooled estimate, for a cut-off value ranged from 135 to 144 mg/dL, produced a sensitivity of 87.2% (95% CI, 85.2-89.0%) and a specificity of 82.6% (95% CI, 81.6-83.6%). The positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR) were 6.48 (95% CI, 3.98-10.57), 0.14 (95% CI, 0.09-0.21), and 45.15 (95% CI, 23.41-87.06), respectively. The area under the curve (AUC) of the summary receiver operating characteristic curve (SROC) was 0.94 (0.92-0.96). When a cut-off value of 2-fold the upper limit of normal was used (ranged from 270 to 280 mg/dL), the pooled sensitivity was 63% (95% CI, 60.0-66.0%), and the specificity was 94.8% (95% CI, 94.1-95.4%). The PLR, NLR, and DOR were 13.3 (95% CI, 7.39-24.0), 0.41 (95% CI, 0.29-0.58) and 33.42 (95% CI, 13.88-80.43), respectively. The AUC of the SROC was 0.92 (0.90-0.94).Only a relatively small number of studies were included, and significant heterogeneity was observed in this meta-analysis.Serum IgG4 is a modestly effective marker to diagnose IgG4-RD. Doubling the cut-off value for IgG4 could not improve the overall test characteristics. A high specificity inevitably accompanies with a significant sacrifice in sensitivity.

IgG4-related Kidney Disease Mimicking Malignant Ureter Tumor: Case Report and Literature Review

Immunoglobulin G4-related disease is a recently recognized systemic disease that can affect any organ or tissue in the body, including the kidneys. IgG4-related kidney disease (IgG4-RKD) is an important part of immunoglobulin G4-related disease. The most common renal manifestation of IgG4-RKD is tubulointerstitial nephritis and glomerular lesions. There, however, is few case of IgG4-RKD mimicking malignant ureter tumor leading to severe hydronephrosis. We herein report an unusual case of IgG4-RKD mimicking malignancy.A 66-year-old Asian man presented to the nephrologist with soreness of loins, anorexia, and acute kidney injury in 2010. His renal function spontaneously improved after 2 weeks' hemodialysis without systemic steroid therapy. Four years later, he presented to the urologist with severe left hydronephrosis because of marked thickness of the left ureter wall. As a ureteral malignancy could not be ruled out, laparoscopic nephroureterectomy was performed.IgG4-related kidney disease was confirmed by the histologic examination. Then, repeat laboratory test showed almost complete recovery of renal function after initiation of steroidal therapy.This case highlights the rare possibility of IgG4-RKD mimicking malignant ureter tumor. Nephrologist and pathologists should be aware of the possibility that hydronephrosis with ureter obstruction may be involved in IgG4-RKD.