June 2026 Research Update

Across these papers, a consistent message was that IgG4-related disease is diagnosed by putting several pieces together, rather than relying on one test alone. Imaging can show where disease may be active, blood tests can support the picture, and tissue testing can be important when the diagnosis is uncertain or when other diseases could look similar. [1] [2] [3] [4] [5] [6]

A Japanese study focused on cardiovascular and retroperitoneal disease found that the 2019 ACR/EULAR classification approach correctly ruled out most mimicking conditions (high specificity 96%), but it missed about one-third of true cases overall (sensitivity 67%). In the subset who had a cardiovascular or retroperitoneal biopsy, sensitivity improved to 78%, supporting the idea that tissue testing can add useful certainty in these locations. [2]

For retroperitoneal fibrosis, a Russian single-center series described a typical diagnostic workup that brought together symptoms, lab signals, imaging patterns, and biopsy features. In this cohort, serum IgG4 was above 1.35 g/L in 82%, and among those biopsied, lymphoplasmacytic inflammation was seen in 100% and fibrosis in 87%, showing how blood tests and tissue findings can point in the same direction but are not identical. [4]

For IgG4-related hypertrophic pachymeningitis (inflammation and thickening of the brain covering), a retrospective analysis reported that people with ANCA-positive blood tests had headaches in 100% and diffuse dural thickening on MRI in 100%, compared with lower rates in ANCA-negative cases. The authors still emphasized that pathology (tissue confirmation) remains essential for diagnosis because blood test patterns can overlap with other inflammatory diseases. [3]

Two pathology-focused papers highlighted why IgG4 staining by itself is not always enough. A liver pathology case series noted that some inflammatory liver tumors can include IgG4-positive plasma cells, creating pitfalls that require additional tests (such as EBV testing and other immune markers) to reach the right diagnosis. [5]

A single-patient report described a man with digestive tract lesions that behaved like IgG4-related disease but a separate liver mass that later proved to be a rare tumor (follicular dendritic cell sarcoma). The authors used this case to illustrate that IgG4-related disease can coexist with other conditions, and that repeated or broader tissue testing may be needed when one organ does not follow the same pattern as the others. [6]

A French clinical practice guideline described diagnosis as a combination of clinical and imaging clues (for example pancreas, salivary or lacrimal glands, aorta, kidneys, and others), blood findings (including higher IgG4 and complement consumption), and biopsy confirmation when possible. This reflects the broader theme that diagnosis is often a structured process aimed at avoiding mislabeling other diseases as IgG4-related disease. [1]

For patients, these studies mainly reinforce that IgG4-related disease can look like other illnesses, and different organs may require different kinds of confirmation (imaging, blood tests, and sometimes tissue sampling). This is most immediately relevant when the disease involves the aorta/retroperitoneum, the brain covering (pachymeningitis), or the liver, where look-alike conditions and overlapping test results were repeatedly discussed. What remains uncertain is how well any single approach performs across all countries and organ types, since several reports were organ-specific, single-center, or included rare situations like a coexisting tumor.

Two papers looked at tools that could support diagnosis beyond standard clinical evaluation: specialized whole-body imaging and measurement of gut bacteria patterns in stool. Both aim to add information about where disease is in the body or whether a person has a measurable disease signature, but both require careful interpretation because they do not replace tissue confirmation or clinical judgment. [7] [8]

A systematic review pooling three studies (90 patients) compared two types of PET/CT scans used to map disease in the body. The fibrosis-focused scan showed higher signal in organs like the pancreas and salivary glands and detected more total lesions (136 vs 78), while the inflammation-focused scan detected more lymph node activity, suggesting the two scans highlight different parts of the disease process. [7]

In a German cross-sectional study, people with IgG4-related disease had reduced gut microbiome diversity and shifts in which bacteria were more common. A machine-learning model based on flow-cytometry microbiome features distinguished patients from healthy controls with AUROC 0.90 in a training set and 0.78 in a small validation set, but the authors described this as proof-of-concept and noted that larger, multi-center validation is needed. [8]

For patients right now, these studies are best viewed as background research about how diagnosis and disease mapping might improve over time. The imaging review suggests that different scan types may be complementary for showing organ involvement, while the microbiome study suggests a future possibility of adding a stool-based signature to the diagnostic toolkit. Key uncertainties include whether these approaches work equally well across all organ types, how results change with medications (many microbiome participants were already on immune treatments), and how much they add beyond established diagnostic steps.

Across this group of studies, researchers focused on antibody-based treatments aimed at controlling IgG4-related disease activity while reducing the need for glucocorticoids (steroids). The strongest evidence came from a phase 3 randomized trial showing fewer flare-ups and more remissions over 52 weeks with obexelimab, while an early-stage report highlighted the need for long-term real-world safety tracking. [9] [10]

In a phase 3 double-blind randomized trial in 194 adults with active IgG4-related disease, weekly obexelimab delayed the time to the first flare that required rescue treatment compared with placebo. It also increased the share of people in complete remission at week 52 and lowered the total amount of steroid rescue used over the year. [9]

Safety in the obexelimab trial was broadly similar between groups, with some side effects occurring more often with obexelimab (including joint aches, hypersensitivity-type reactions, and diarrhea), while serious adverse events were reported less often than with placebo. This suggests the treatment effect was not achieved by simply increasing overall serious complications in that trial population. [9]

A separate paper described the planned 4SigHT Study in Japan, which will follow about 100 people starting inebilizumab in usual clinical practice and track flare-ups through 52 weeks, with safety follow-up planned for up to 6 years. Because this is a protocol paper, it does not yet report results, but it shows that longer-term, real-world effectiveness and safety are being studied. [10]

In a multicentre retrospective case series of 18 people with treatment-refractory autoimmune diseases, only one of whom had IgG4-related disease (most had systemic sclerosis), one cycle of teclistamab produced major clinical responses in 61% of patients overall, along with B-cell depletion and lower autoantibody levels. However, substantial safety issues were reported, including cytokine release syndrome episodes, severe low antibody levels in all patients, infections, and two deaths in patients with advanced heart involvement from systemic sclerosis. The published summary does not say separately how the one person with IgG4-related disease did. [11]

For patients and caregivers, this month’s treatment research most clearly adds evidence that a non-depleting B-cell antibody approach (obexelimab) can reduce flare-ups and reduce steroid rescue use over about 1 year in adults with active IgG4-related disease, based on a high-quality randomized trial. Longer-term experience with other B-cell-targeting therapy (inebilizumab) is still being collected in routine-care settings, so questions about durability and long-term safety remain open. More intensive immune-redirecting therapy (teclistamab) was reported in a small retrospective series of hard-to-treat autoimmune diseases that included only one person with IgG4-related disease, and came with important infection and immune-suppression risks, so its role in IgG4-related disease is uncertain from these data alone. [9] [10] [11]

One report focused on rituximab maintenance treatment in a person with IgG4-related pancreatitis and IgG4-related kidney inflammation (tubulointerstitial nephritis), highlighting how relapse control and kidney outcomes were tracked over time. Because it is a single case report, it shows what happened for one individual and cannot predict what will happen for most people. [12]

The case described a 69-year-old man who developed acute kidney injury while on rituximab and then received a more intensive rituximab maintenance schedule. After this change, the report described longer relapse-free survival at 12 months and continued kidney remission over 2 years, including stable kidney-related lab markers. [12]

In this patient, the authors reported no severe infections and no hypogammaglobulinemia during rituximab therapy, which are side effects often watched for with B-cell targeted treatments. The report also noted improvement in blood complement levels alongside remission, linking lab changes with the clinical course in this individual. [12]

This case report is most relevant as background for people affected by IgG4-related kidney disease, because it describes long-term follow-up and monitoring during rituximab maintenance in one person rather than results from a larger study. It suggests that sustained kidney remission can occur with ongoing rituximab in some situations, while also showing the kind of infection and antibody-level monitoring clinicians may use. What remains uncertain is how often similar results occur in broader IgG4-related disease populations and which patient groups might benefit or face higher risks, since this report does not include a comparison group. [12]

Across these studies, relapse risk was linked most strongly to measurable shifts in the immune system over time, rather than to broad, non-specific inflammation blood tests. One study in people treated with rituximab connected relapse with the return of a particular IgG4-producing plasma cell type and coordinated changes in T-cell subsets. A smaller newly diagnosed cohort suggested that certain cytokines and B-cell markers moved along with disease activity, while common markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) showed only limited connections. [13] [14]

In a moderate-sized longitudinal analysis during rituximab-related B-cell depletion, researchers identified a disease-specific NMU-expressing IgG4+ plasma cell subset with skewed IGHV1-69 antibody gene usage, seen in blood and also in affected tissues. Over time, immune patterns shifted with clinical course: remission and relapse were mirrored by changes in circulating helper T cells (Tfh cells) and double-negative T cells, alongside reconstitution of the proposed pathogenic plasma cells. The authors proposed these NMU+ IGHV1-69+ IgG4+ plasma cells as a driver of recurrence and as a candidate marker to track risk of relapse. [13]

In a small, single-center prospective study of 10 newly diagnosed, treatment-naive patients followed for 12 months, disease activity scores decreased over time while blood IgG4 also fell by 12 months. Higher disease activity was linked to higher levels of several cytokines (including interferon-gamma, IL-10, IL-13, and IL-5), higher total IgG, and higher eosinophils, and it was linked to a lower plasmablast-to-IgG4 ratio. PET-positive scans were linked to higher total IgG, while CRP related more to a separate damage index than to overall activity, supporting the idea that standard inflammation markers may not closely reflect IgG4-related disease activity in some settings. [14]

For patients and caregivers, these papers add background evidence that flare or relapse may be preceded or accompanied by specific immune changes that can be measured in blood, especially in people being followed over time (including during rituximab-related B-cell depletion). However, the proposed markers are not yet established for routine care: one study focused on detailed multi-omics profiling, and the other was very small and exploratory, so it is still uncertain which signals will hold up across different organs affected by IgG4-related disease and in larger, more diverse groups. [13] [14]

Across two case reports, IgG4-related disease (IgG4-RD) involved major cardiovascular structures (the sac around the heart and the aorta) and presented like other urgent conditions, making recognition difficult in real time. In both reports, the clearest confirmation came from examining tissue under the microscope rather than blood tests or scans alone. Because these are single-patient descriptions, they show what can happen but cannot estimate how often it occurs or predict outcomes for most people. [15] [16]

In one patient, IgG4-RD first showed up as constrictive-effusive pericarditis (fluid around the heart plus a stiff heart lining), with shortness of breath, swelling, and fluid buildup. The diagnosis was confirmed by pericardial tissue after open-heart surgery, where fibrosis and many IgG4-positive immune cells were seen. Steroids led to severe high blood sugar, an interleukin-1 blocker (rilonarcept) did not improve the constriction, and remission was maintained after surgery with rituximab. [15]

In another patient, IgG4-RD affected the aorta (IgG4-related aortitis) and closely mimicked an acute aortic problem with severe chest pain and collapse, including scan findings that suggested an intramural hematoma. During emergent surgery, the inner aortic surface looked normal, and the diagnosis was made only after histopathology showed IgG4-positive cells and a characteristic fibrotic pattern. The patient died during surgery, underscoring how quickly this presentation can deteriorate and how hard it can be to distinguish from other emergencies using imaging alone. [16]

For patients and caregivers, this month’s cardiovascular papers mainly add background about rare but serious ways IgG4-RD can involve the heart lining (pericardium) or the aorta, sometimes resembling other urgent heart or aortic conditions. These reports suggest that blood IgG4 levels may not always be clearly abnormal and that tissue examination can be the deciding test when it is possible to obtain safely. What remains uncertain is how often these presentations occur, which tests best separate IgG4-RD from look-alike emergencies early on, and which treatments work best across larger groups of patients.

Across three single-patient reports, IgG4-related disease affected the lungs and/or kidneys and initially looked like other conditions (such as infection, scarring-type lung disease patterns on scans, or other causes of kidney inflammation). A consistent message was that diagnosis depended on getting enough tissue for the typical microscopic pattern, because smaller biopsies or blood tests alone could be misleading. Responses after steroid treatment ranged from clear improvement on scans to only partial organ recovery, especially when kidney damage was advanced. [17] [18] [19]

In one report, a 32-year-old woman with a persistent lung mass had two non-diagnostic needle biopsies and was initially treated for tuberculosis, but surgical removal of the mass provided enough tissue to confirm IgG4-related lung disease based on characteristic scarring and inflammation patterns. Her blood IgG4 level was normal, but the tissue showed a high proportion of IgG4-positive plasma cells, and she remained well after starting steroids. [17]

Another report described a man in his 60s with IgG4-related disease limited to the kidneys and lungs, where imaging showed enlarged kidneys and lung changes that mimicked a scarring-type lung condition. A thoracoscopic lung biopsy confirmed IgG4-rich inflammation and helped unify the diagnosis across both organs, and steroid treatment improved both symptoms and imaging. [18]

A third report described a 49-year-old man with salivary and eye gland swelling (a Mikulicz disease pattern) and biopsy-proven IgG4-related tubulointerstitial nephritis, with very high blood IgG4. Prednisone improved gland symptoms and lowered urine protein, but kidney function improved only slightly and later worsened; after a severe lung infection and sepsis during immunosuppressive therapy, he developed kidney failure requiring long-term dialysis. [19]

For patients and caregivers, this set of reports mainly adds background context rather than providing firm predictions, because each paper describes only one person. Together, they highlight that lung and kidney involvement from IgG4-related disease can resemble other illnesses on scans and may require a larger or surgical biopsy to confirm, and that a normal blood IgG4 level does not rule it out. They also show that while steroid treatment can lead to clearer improvement in symptoms and imaging in some situations, kidney recovery may be incomplete when there is already significant scarring, and serious infections can occur during immune-suppressing treatment, making outcomes harder to interpret.

In these June 2026 reports, IgG4-related disease (IgG4-RD) repeatedly looked like cancer on imaging because it formed mass-like inflammation in several organs, including the liver, stomach, breast, and abdominal lining. The overall pattern was that scans alone could not reliably separate IgG4-RD from cancer, and tissue sampling was often needed to confirm the cause, sometimes after an initial biopsy did not give a clear answer. Because these are individual case reports, they show what can happen but cannot tell how often it happens or what the usual outcome is. [20] [21] [22] [23] [24] [25]

Several cases involved the liver, where imaging suggested malignancy but later testing supported IgG4-RD. One 52-year-old man had liver changes and widespread active lymph nodes on a whole-body scan that led to biopsy confirmation of IgG4-RD and improvement after glucocorticoids. [20]

Another liver case involved a 72-year-old woman whose liver mass and portal vein thrombosis (a blood clot in a major liver vessel) resembled liver cancer; the first biopsy was not diagnostic, but repeat tissue testing confirmed IgG4-RD, and prednisone was followed by marked clinical and scan improvement with reopening of the portal vein. This report also noted that a normal blood IgG4 level did not rule out IgG4-RD in that patient. [22]

Masses in the digestive tract also created major uncertainty. A 26-year-old woman had a stomach wall mass that was active on PET imaging; repeated needle biopsies did not provide a diagnosis, and a steroid trial did not change symptoms or imaging, so surgery was performed and the final surgical tissue confirmed IgG4-RD. In a separate case, a woman in her late 20s had an omental (abdominal lining) mass with IgG4-positive cells on biopsy, improved on high-dose glucocorticoids but could not taper below a certain dose, and later had symptom resolution with rituximab along with near improvement on imaging. [21] [24]

IgG4-RD can also present as breast lumps. A 40-year-old woman had lumps in both breasts and underarm lymph node enlargement, with contrast-enhanced breast imaging showing multiple small masses; biopsy confirmed IgG4-related mastitis as part of systemic IgG4-RD, and corticosteroids were followed by rapid improvement and full imaging resolution of breast masses at 6 months. [23]

One report described overlap between cancer and IgG4-RD changes in the liver. A 71-year-old man with previous rectal cancer had a liver metastasis that showed spontaneous regression along with IgG4-rich inflammatory pseudotumor-like changes and evidence of systemic IgG4-RD, and he remained recurrence-free 20 months after surgical resection without chemotherapy or steroids. Because this is a single case, it does not show whether IgG4-RD can generally affect cancer behavior. [25]

For patients and caregivers, these reports mainly serve as background to explain why IgG4-RD can sometimes be discussed in the same breath as cancer: it can create lump-like areas on scans in organs such as the liver, stomach, breast, and abdominal lining, and first-round biopsies may not always settle the question. They also show that blood IgG4 levels and scan appearance were not consistently decisive across cases, so uncertainty can persist until enough tissue is examined. What remains unclear is how common these situations are and which imaging or biopsy approaches work best, because all evidence here comes from individual case reports rather than larger studies. [20] [21] [22] [23] [24] [25]

Across these reports, IgG4-related disease showed up in different ways around the eye (surface of the eye and the orbit) and could also be considered when evaluating certain plasma-cell rich skin conditions. The overall message was that tissue testing helped confirm the cause, and blood IgG4 levels were not always high even when the diagnosis was confirmed. [26] [27] [28]

One patient had IgG4-related disease limited to the conjunctiva, where it looked like a common, benign-appearing eye-surface spot. Diagnosis was made after the lesion was removed and tested with IgG4 staining, and the report described complete remission at 6 months after topical glucocorticoid treatment for suspected local recurrence. [26]

In a small pediatric case series of three girls, IgG4-related orbital disease presented with progressive eye bulging and lacrimal gland involvement, and some had exposure-related corneal problems or vision effects. All had diagnosis confirmed by tissue testing; one patient who did not respond well at first had marked improvement after rituximab was added, while the others improved and were stable over follow-up reported to 1 year. [27]

Two adult men with cutaneous plasmacytosis were reported to illustrate how certain skin biopsy patterns and blood test results can overlap with IgG4-related disease and with multicentric plasmacytic Castleman disease. One case was treated as Castleman disease and had partial remission with an interleukin-6 targeted antibody plus other therapies, while the other had IgG4-related features and remained stable over 12 months without treatment. [28]

For patients, this set of papers mainly serves as background on the range of ways IgG4-related disease can involve the eye area and how some skin conditions may resemble it on biopsy or bloodwork. Because these are single-patient reports and a three-patient series, they cannot show how common these presentations are or predict what will happen for most people, but they highlight that confirming the diagnosis often depends on tissue examination and that blood IgG4 levels may be normal in some confirmed cases. [26] [27] [28]