Utility of FDG PET/CT for Differential Diagnosis of Patients Clinically Suspected of IgG4-Related Disease

PET/CT in Inflammatory and Auto-immune Disorders: Focus on Several Key Molecular Concepts, FDG, and Radiolabeled Probe Perspectives

Chronic immune diseases mainly include autoimmune and inflammatory diseases. Managing chronic inflammatory and autoimmune diseases has become a significant public health concern, and therapeutic advancements over the past 50 years have been substantial. As therapeutic tools continue to multiply, the challenge now lies in providing each patient with personalized care tailored to the specifics of their condition, ushering in the era of personalized medicine. Precise and holistic imaging is essential in this context to comprehensively map the inflammatory processes in each patient, identify prognostic factors, and monitor treatment responses and complications. Imaging of patients with inflammatory and autoimmune diseases must provide a comprehensive view of the body, enabling the whole-body mapping of systemic involvement. It should identify key cellular players in the pathology, involving both innate immunity (dendritic cells, macrophages), adaptive immunity (lymphocytes), and microenvironmental cells (stromal cells, tissue cells). As a highly sensitive imaging tool with vectorized molecular probe capabilities, PET/CT can be of high relevance in the management of numerous inflammatory and autoimmune diseases. Relying on key molecular concepts of immunity, the clinical usefulness of FDG-PET/CT in several relevant inflammatory and immune-inflammatory conditions, validated or emerging, will be discussed in this review, together with radiolabeled probe perspectives.

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.

18F-fluorodeoxyglucose PET and PET/computed tomography for the evaluation of immunoglobulin G4-related disease: a systematic review

BACKGROUND

In the last years, 18F-fluorodeoxyglucose PET/computed tomography (18F-FDG PET/CT) has demonstrated its utility for the evaluation of immunoglobulin G4 (IgG4)-related disease (IgG4RD). The studies are, however, really heterogeneous and different. The aim of this review is, therefore, to analyze the diagnostic performance of 18F-FDG PET and PET/CT for the assessment of IgG4RD.

METHODS

A wide literature search of the PubMed/MEDLINE, Scopus, Embase and Cochrane library databases was made to find relevant published articles about the diagnostic performance of 18F-FDG PET or PET/CT for the evaluation of IgG4RD.

RESULTS

The comprehensive computer literature search revealed 779 articles. On reviewing the titles and abstracts, 756 articles were excluded because the reported data were not within the field of interest. Twenty-three studies were included in the review.

CONCLUSION

Despite some limitations that affect our review, 18F-FDG PET or PET/CT demonstrated the ability to assess IgG4RD both at initial evaluation and after therapy. In general, no correlation between PET/CT parameters and IgG4 serum levels has been reported. A possible role for 18F-FDG PET/CT to drive differential diagnosis with other disease is starting to emerge.

The role of imaging in immunoglobulin G4-related disease of the upper urinary tract

Background

Immunoglobulin G4-related disease remains a modern, relatively unknown field in the urological world. An increasing number of cases require urological input, often with invasive diagnostics and aggressive medical treatment first-line. Given this, we sought to evaluate modern radiological options of disease affecting the upper urinary tract, to provide clarity and reduce diagnostic burden and delay in this poorly understood yet potentially debilitating disease process.

Summary

We conducted a systematic literature search including PubMed and Medline, focusing on immunoglobulin G4-related disease affecting the upper urinary tract, before reviewing articles assessing different radiological modalities in diagnosis. Consistent computed tomography findings have been demonstrated in the literature and contributed to recent breakthroughs in classification criteria, however invasive biopsy remains a mainstay in work-up, given the difficulties in comparing against malignancy. Early work in positron-emission tomography and magnetic resonance imaging has shown promise in radiologically distinguishing from other differentials, especially diffusion-weighted imaging showing high sensitivity levels, but not yet enough to formulate protocols and cause histological investigation to be redundant.

Key messages

Our article has highlighted repeated findings in the literature of computed tomography appearances of IgG4-RD in the upper urinary tract, however invasive work-up remains a mainstay given the overlap with malignancy. Prospective, comparative studies into magnetic resonance imaging and positron-emission tomography are now required, given their early results, to improve consistency in reporting and reduce patient burden when investigating this benign, yet debilitating disease process.

Clinical value of 18F-FDG PET/CT in IgG4-related disease

OBJECTIVE

To investigate the clinical value of ¹⁸F-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) in IgG4-related disease (IgG4-RD).

METHODS

Seventy two patients diagnosed with IgG4-RD who underwent PET/CT were included. Correlations between clinical variables and PET/CT findings were analyzed by Spearman's correlation test. Conventional radiology was compared to PET/CT to evaluate detection discrepancies. The detection ability of insidious organ involvement by PET/CT at disease onset was investigated. The utility value of PET/CT for the 2019 ACR/EULAR classification criteria was analyzed with the multivariate logistic analysis and ROC curve.

RESULTS

SUV_max of main involved organ was positively correlated with IgG4-RD Responder Index (IgG4-RD RI), serum and tissue IgG4 levels and IgG4/IgG ratio, serum eosinophils counts and number of involved organs, while negatively correlated with serum IgM levels. PET/CT was superior in detecting organ/tissue involvements including prostate, gastrointestinal tract and lung compared with conventional imaging. For patients with pancreato-hepato-biliary or head-neck involvements at onset, PET/CT showed superiority in detecting insidious lesions. Multivariate analysis showed that disease duration, multiple-organ involvement, SUV_max of main involved organ and mean SUV_max of all involved organs were significantly associated with the fulfillment of the 2019 ACR/EULAR classification criteria. ROC curves indicated that the cut-off value for SUV_max of main involved organ and mean SUV_max of all involved organs for fulfillment of the 2019 ACR/EULAR classification criteria for IgG4-RD were 4.1 and 3.5, respectively.

CONCLUSION

¹⁸F-FDG PET/CT has potential capacity to monitor disease activity, evaluate organ involvements and assist in the classification criteria in IgG4-RD.

Active IgG4-related disease with bone marrow involvement: a report of 2 cases and case-based review

IgG4-related disease (IgG4-RD) is a systemic fibro-inflammatory disease, histopathologically characterized by dense lymphoplasmacytic infiltration rich in IgG4-positive plasma cells in affected organs. Classic hematologic presentations including lymphadenopathy, eosinophilia and polyclonal hypergammaglobulinemia are common, whereas bone marrow involvement of IgG4-RD is rarely reported. Here we present two patients of multi-organ IgG4-RD with bone marrow involvement, one on bone marrow biopsy, and the other on PET/CT. Presentations of other organ involvement included biopsy-proven IgG4-related tubulointerstitial nephritis, lymphadenopathies, submaxillary glands, arteritis, asthma, dysosmia, and constitutional symptoms. Bone marrow involvement was initially suspected due to leukopenia, anemia and thrombocytopenia in case#1, and was finally confirmed by histological evidence of significant IgG4-positive plasma cells infiltration in bone marrow. In case#2, we incidentally observed high uptakes of multi-bone marrow on ¹⁸F-FDG-PET/CT, with the maximum SUV value similar to that of the kidneys, submaxillary glands and hilar, mediastinal lymph nodes by ¹⁸F-FDG-PET/CT. Symptoms and all the hematologic presentation improved rapidly in both patients after steroids initiation. These two cases illustrate the rare bone marrow involvement in active IgG4-RD accompanied by other hematologic syndromes. The significance of disease pathogenesis is worthy of further study.

Multimodality Imaging of Large Vessel Vasculitis, From the AJR Special Series on Inflammation

Large vessel vasculitis (LVV) is a non-infectious inflammation of the large vessels, including the aorta and its main branches. Imaging plays an essential role in diagnosing LVV, given the challenges of tissue biopsy. This article reviews the types of LVV, and the multimodality imaging tools available to establish the diagnosis in patients with LVV. The cornerstone of imaging diagnosis is morphologic assessment using grey-scale ultrasound, combined grey-scale US with color Doppler US, CTA, or MRA. In the last decade, substantial progress has been made in functional and molecular imaging with FDG PET/CT for the diagnosis of LVV. Investigation is ongoing to develop novel MRA techniques and new PET tracers to assess disease activity and to differentiate the various vasculitides. An algorithm is provided to guide imaging technique selection based on the patient's specific clinical presentation.

IgG4 Related Kidney Disease with Extra-Renal Involvement Demonstrated on FDG PET/CT

Immunoglobulin G4 (IgG4)-related kidney disease is a relatively rare clinical entity and usually occurs as an extra-pancreatic manifestation of IgG4-related autoimmune pancreatitis. We describe here the imaging findings of a patient who presented with recurrent multiorgan IgG4-related disease, involving bilateral kidneys/ureters, proximal small bowel, and multiple abdominal and extra-abdominal lymph nodes.

The neurology of IGG4-related disease

PURPOSE OF REVIEW

IgG4-related disease (IgG4-RD) is emerging as a fibro-inflammatory entity affecting multiple organs, including manifold neurologic manifestations. This review discusses general characteristics of IgG4-RD neurologic disease including epidemiology, histology, clinical picture and treatment approaches.

RECENT FINDINGS

IgG4-RD is increasingly recognized as an important underlying pathophysiology in multiple disorders of neurologic interest, including orbital inflammation, infundibulo-hypophysitis, hypertrophic pachymeningitis, and even in rare cases CNS parenchymal disease and cranial vascular involvement. These were previously considered idiopathic and unrelated to any systemic disease but now known to share a common histopathology. New knowledge regarding the pathogenesis, clinical features and epidemiology of IgG4 is emerging, and new neurological manifestations continue to be described. Diagnostic progress includes CT-PET imaging, the use of flow cytometry for plasmablast quantification, and the use of reverse passive latex agglutination aiming to overcome the prozone phenomenon. Histopathologic confirmation of IgG4-RD remains the gold standard method of diagnosis but new diagnostic criteria for systemic and organ-specific disease are being proposed. Though glucorticoids remain the mainstay of therapy, relapses and incomplete recovery are frequent. Rituximab is a promising treatment in IgG4-RD that is severe, refractory or glucocorticoid dependent. Initiation of immunosuppression at an early stage of disease should be considered in order to avoid development of refractory fibrosis.

SUMMARY

The current review emphasizes the neurologic manifestations of IgG4-RD.

IgG4 related disease

IgG4-related disease (ER-IgG4) is a recognised systemic disease. It was described after patients diagnosed with autoimmune pancreatitis showed signs of extra-pancreatic disease. The clinical manifestation of these patients is subacute and is manifested by the appearance of pseudotumoral lesions, or inflammatory or fibrous tumours. Sometimes it can be serious as in the case of patients with cholangitis or large vessel vasculitis. Diagnostic criteria include, among others, serum IgG4 elevation and/or histological parameters. The 18F-FDG-PET/CT is useful in the initial diagnosis, biopsy guidance as well as in the assessment of response to therapy. It usually responds to steroid therapy.

Features of IgG4-related lung disease on 18F-FDG PET/computed tomography imaging

OBJECTIVES

The aim of the study was to summarize the features of immunoglobulin G4-related lung disease (IgG4-RLD) on fluorine 18-fluorodeoxyglucose (F-FDG) PET/computed tomography (CT).

METHODS

In this retrospective case series, 12 consecutive patients (9 men and 3 women, mean age 55.4 ± 13.7 years) with IgG4-RLD were included. The clinicopathological information and features of F-FDG PET/CT imaging were analyzed.

RESULTS

Six (50%) patients had pulmonary involvement alone and six (50%) patients had extrapulmonary involvement with intense F-FDG uptake. Pulmonary manifestations included mass (25%, 3/12), solid nodule (solitary 25%, 3/12; multiple 50%, 6/12), multiple ground-glass opacities (GGOs) (50%, 6/12), thickening of alveolar interstitium (50%, 6/12), and thickening of bronchovascular bundle (33.3%, 4/12). The maximum standardized uptake value (SUVmax) of the solid nodules and masses, multiple GGOs, bronchovascular bundle and the thickening of septa was 4.0 ± 2.5, 2.3 ± 1.8, 1.4 ± 0.6, and 0.9 ± 0.5, respectively. The SUVmax statistically significant linear association with the diameter of masses or solid nodules (P value = 0.03), but no significant inverse linear association (P value = 0.06) with the concentration of serum IgG4 concentration.

CONCLUSIONS

The image patterns of IgG4-RLD on F-FDG PET/CT are varying. Multiple pulmonary manifestations or multiple organ involvement, especially in combination with elevated levels of serum IgG and IgG4, may help to make the diagnosis. A potential major application of PET-CT would be evaluation of response to treatment, and the impact of PET/CT on IgG4-RLD management is worth investigating further in the future.

A Resected Case of Follicular Cholangitis That Was Positive on 18F-fluorodeoxyglucose-positron Emission Tomography

We experienced a case of follicular cholangitis that was positive on fluorodeoxyglucose-positron emission tomography (¹⁸F-FDG-PET). A 70-year-old man was admitted for jaundice. Endoscopic retrograde cholangiography showed stenosis of the middle to upper choledocus. ¹⁸F-FDG-PET depicted a localized hot spot at the stenotic lesion (maximum standardized uptake value = 8.2). Although no malignant findings were found in the cytology or on a bile duct biopsy, malignancy could not be excluded, so surgical treatment was performed. Follicular cholangitis is a new, rare disease that causes severe biliary stricture. Only 11 cases of follicular cholangitis have been reported, including the present case.

Clinical and imaging findings suggestive of histopathological immunoglobulin G4-related disease: a single-center retrospective study

OBJECTIVE

To investigate the clinical and imaging features predicting the histopathological diagnosis of immunoglobulin G4 (IgG4)-related disease (IgG4RD) in patients with suspected IgG4RD on computed tomography (CT).

METHODS

We retrospectively reviewed the medical records of 178 patients with CT findings suspicious of IgG4RD from January 2015 to December 2017. Patients who underwent tissue biopsy were included to evaluate the association between patient characteristics and histopathological diagnosis of IgG4RD. The histopathological diagnosis was classified into IgG4RD and non-IgG4RD. Clinical, laboratory, and imaging features were compared between patients with IgG4RD and non-IgG4RD, and logistic regression analysis was performed to identify the predictors for histopathologically confirmed IgG4RD.

RESULTS

Of the 103 patients with histopathologically proven diseases, 46 and 57 patients were classified as IgG4RD and non-IgG4RD, respectively. The median age was 64 years; 65% of patients were male. There were significant differences in sex (P = 0.035), fever (P = 0.039), serum IgG4 level (P < 0.001), renal involvement (P = 0.036), lacrimal or salivary glands involvement (P = 0.050), swelling pattern on CT (P = 0.001), and positron emission tomography (PET)-CT findings (P < 0.001) between patients with IgG4RD and non-IgG4RD. Multivariate analysis revealed elevated IgG4 level > 135 mg/dL (odds ratio [OR] = 5.418, P < 0.001), kidney involvement (OR = 6.170, P = 0.044), and the swelling feature on CT (OR = 4.301, P = 0.012) to be independent factors for histopathological diagnosis of IgG4RD.

CONCLUSION

This study suggests that elevated IgG4 level, renal involvement, and swelling pattern on CT are associated with histopathological diagnosis of IgG4RD. The clinical and imaging features might help to decide further evaluation in patients with clinically suspected IgG4RD. Key Points • Computed tomography (CT) is not sufficient to discriminate between IgG4-related disease (IgG4RD) and non-IgG4RD conditions. • Histopathological diagnosis of IgG4RD is associated with elevated IgG4 level, renal involvement, and swelling pattern on CT. • Positron emission tomography-CT may be a useful diagnostic tool in patients with clinically suspected IgG4RD. >.

Salivary gland involvement disparities in clinical characteristics of IgG4-related disease: a retrospective study of 428 patients

OBJECTIVES

IgG4-related disease (IgG4-RD) has recently been recognized as a fibro-inflammatory condition featuring tumefactive lesions in multiple organs, and the salivary gland is one of the most commonly involved sites. We undertook this study to compare detailed demographic, clinical and laboratory characteristics of IgG4-RD patients with salivary gland lesions (IgG4-RD SG+) and salivary-gland-free IgG4-RD (IgG4-RD SG-) in a large cohort.

METHODS

We carried out a retrospective review of the medical records of 428 cases of IgG4-RD diagnosed at Peking University People's Hospital between March 2006 and May 2018.

RESULTS

Among 428 patients, 249 had salivary glands that were affected. IgG4-RD SG+ patients showed younger age at disease onset and diagnosis, and a longer interval between symptom onset and diagnosis. The IgG4-RD SG+ group involved more female patients, and allergic diseases were more common in this group. In terms of organ involvement, the IgG4-RD SG+ group were more frequently presented with lacrimal gland involvement, while lymph node, retroperitoneal fibrosis, pancreas, biliary system, kidney and aorta were more prominent in the IgG4-RD SG- group. In addition, the serum IgG4 level, IgG4/IgG ratio and IgE level were significantly higher in IgG4-RD SG+ patients. Patients with eosinophilia were more common in the IgG4-RD SG+ group, while elevated ESR, CRP and positive ANA were more common in the IgG4-RD SG- group.

CONCLUSION

We have revealed demographic, clinical and laboratory differences between IgG4-RD SG+ and SG- patients, which indicated potential differences in pathogenesis and important implications for the diagnosis and management of these two phenotypes.

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.

Fibroblast Activation Protein-Targeted PET/CT with 68Ga-FAPI for Imaging IgG4-Related Disease: Comparison to 18F-FDG PET/CT

IgG4-related disease (RD) is characterized by lymphoplasmacytic infiltration enriched in IgG4-positive plasma cells and variable degrees of fibrosis with a characteristic storiform pattern. Since fibrosis is an important feature of IgG4-RD, we performed a prospective cohort study to evaluate the performance of ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI), a recently introduced PET agent targeting fibroblast activation protein, in IgG4-RD. Methods: Twenty-six patients with IgG4-RD were recruited. All patients underwent both ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT. The positive rates of the PET/CT scans in the involved organs and the uptake values were compared. Results: In a total of 136 involved organs in the 26 patients, ⁶⁸Ga-FAPI PET/CT additionally detected 18 (13.2%) involved organs in 13 (50.0%) patients, compared with ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI PET/CT had a higher positive rate than ¹⁸F-FDG PET/CT in detecting involvement in the pancreas, bile duct/liver, and lacrimal gland. ⁶⁸Ga-FAPI also demonstrated significantly higher uptake than ¹⁸F-FDG in the matched disease in the pancreas, bile duct/liver, and salivary gland (P < 0.01). However, lymph node involvement with flip-flop uptake of ¹⁸F-FDG did not accumulate ⁶⁸Ga-FAPI. Conclusion: ⁶⁸Ga-FAPI might be a promising imaging agent for the assessment of IgG4-RD.

Pleural, pancreatic and prostatic involvement in IgG4-related disease mimicking pancreatic head malignancy

We describe the case of a gentleman with pleural thickening. On follow-up imaging, dilatation of the main pancreatic and common biliary ducts was noted and an initial diagnosis of pancreatic malignancy was made. During his preoperative workup for pancreatic head malignancy, a PET-CT was performed, which demonstrated increased uptake in the pancreas, in the pleura and in the prostate gland. This raised the possibility of immunoglobulin G4-related disease (IgG4-RD), which was effectively treated with oral steroids. IgG4-RD is a well-described cause of autoimmune pancreatitis but can affect other regions, including the pleura and prostate. It is essential that radiologists are aware of the imaging findings in IgG4-RD and can direct clinicians towards this important multisystem diagnosis.

Isolated Immunoglobulin G4-Related Disease of Nasal Septum and Maxilla: Diagnosis and Follow-up With 18F-FDG PET/CT

Immunoglobulin G4-related disease (IgG4-RD) is a systemic inflammatory condition that can manifest in atypical locations. We present the case of a middle-aged woman presenting with isolated IgG4-RD of left maxilla and nasal septum, confirmed with F-FDG PET/CT. She achieved complete metabolic response with multiple pharmacologic treatment, but 1 year later, she experienced local relapse, and FDG PET/CT found new additional lesions in humeral vasculature and lungs. This case illustrates the usefulness of FDG PET/CT for initial evaluation and monitoring of IgG4-RD with unusual nasomaxillary involvement.

Hypophysitis (Including IgG4 and Immunotherapy)

Hypophysitis is characterized by inflammation of the pituitary gland that can be primary (PH) or secondary (SH) to other diseases or following drug administration. It may also be classified according to anatomical and histopathological criteria, leading to variable degrees of hypopituitarism and/or compressive symptoms to nearby structures. There has recently been an increase in the number of hypophysitis cases, raising the interest on the spectrum of its pathogenesis, clinical, biochemical/endocrinological, and imaging features. However, the use of conventional biomarkers, including currently utilized pituitary autoantibodies, has relatively limited diagnostic accuracy. Lymphocytic hypophysitis (LH) is the commonest cause of PH, whereas IgG4-related hypophysitis is increasingly being recognized. Histiocytosis and granulomatous diseases are the most frequent causes of SH, although infections and lymphoma have also been reported. The increasing use of immune checkpoint inhibitors in oncology is associated with a high incidence of hypophysitis, providing further understanding of its pathogenesis. Hypophysitis can occur silently and be easily missed, potentially leading to substantial morbidity or mortality due to adrenal insufficiency, requiring a high index of clinical suspicion and timely initiation of appropriate treatment. In most cases of LH or drug-induced hypophysitis, active surveillance along with replacement of established hormonal deficiencies is needed. In the presence of compressive and/or evolving symptoms, treatment with glucocorticoids either alone or in combination with other immunosuppressive agents can be used. Surgical decompression is reserved for nonresponsive cases with threatened vital structures. Timely diagnosis and intervention are important to minimize disease-related morbidity and mortality. We aimed to review current concepts and recent developments in the pathogenesis, diagnosis, and management of hypophysitis.

IgG4-Related Tumefactive Lesions at the Pulmonary Artery Causing Stenosis of Bilateral Primary Branches and Resultant Pulmonary Hypertension

IgG4-related disease (IgG4-RD) is a newly recognized but rare entity involving multiple organs, with autoimmune pancreatitis, retroperitoneal mass, and the inflammation of glands being typical in most cases. IgG4-related perivascular lesions, although uncommon, have been increasingly reported in recent years. Diagnosis of IgG4-RD relies on comprehensive consideration of characteristic histopathological and immunostaining results, clinical and imaging findings, and serological results according to several widely recognized diagnostic criteria. This benign disorder frequently presenting tumefactive lesions should be distinguished from malignancy and other inflammatory mimics. Here we report a case of tumefactive mass at the bifurcation of the pulmonary trunk causing stenosis of the proximal left and right pulmonary artery (PA) and resultant pulmonary hypertension (PH). Bypass from the PA trunk to the right branch distal to stenosis was performed to resolve the obstructive hemodynamic disturbance and PH. Glucocorticoid monotherapy was performed after a diagnosis of definite IgG4-RD. Longitudinal disease activity assessment via imaging modalities, serological parameters, and IgG4-RD responder index verified no relapse during follow-up and the validity of the treatment strategy.

Therapeutic Response to Rituximab in IgG4-Related Hypophysitis Evidenced on 18F-FDG PET and MRI

Baseline F-FDG PET and MRI were performed in a patient with IgG4-related hypophysitis, showing a 15-mm hypervascular hypermetabolic lesion with sellar and suprasellar extension. Lack of response after 10 months of first-line corticosteroid therapy was demonstrated on both F-FDG PET and MRI. Three months later, after 2 injections of 1 g of rituximab associated with continued corticosteroid therapy, MRI showed substantial shrinkage of the pituitary lesion with minimal residual Gd enhancement, whereas F-FDG PET evidenced complete metabolic response. As such, joint F-FDG PET and MRI assessment during therapy may have a potential interest for treatment response evaluation in pituitary IgG4-related disease.

Immunoglobulin G4-related hypertrophic pachymeningitis: A case-oriented review

Objective

Meningeal involvement in Immunoglobulin G (IgG)-4-related disease is rare and only described in case reports and series. Because a review into the disease is lacking, we present 2 cases followed by a literature review of IgG4-related hypertrophic pachymeningitis (IgG4-HP).

Methods

Two IgG4-HP cases were reported, one involving the spinal cord and responding to surgical management and a second involving the brain and responding to Rituximab therapy. We then review clinical cases and case-series of histologically proven IgG4-HP that were published in the PubMed-NCBI database.

Results

Forty-two case reports and 5 case-series were studied (60 patients, 20 women). The median age was 53. Eighteen patients had systemic involvement and 24 had single-organ IgG4-HP. Fifty-five percent of patients had an elevated serum IgG4. Treatment was surgical in 20/53 cases. Steroid therapy and immunosuppressors were effective in 85% and more than 90% of the cases, respectively. The rate of disease relapse was 42.1% after steroid therapy was discontinued.

Discussion/conclusion

IgG4-HP is characterized by the lack of extra-neurologic organ-involvement and systemic signs. Histopathologic studies should be performed as it is crucial for diagnosis because serum markers are rarely informative. 18F-FDG positon tomography can be useful to characterize systemic forms. There is no specific CSF marker for IgG4-HP and the diagnostic value of CSF IgG4 levels needs to be studied with larger samples. We provide a treatment algorithm for IgG4-HP. Such treatment strategies rely on early surgery, steroids, and early immunosuppressive therapy to prevent neurologic complications.

Elevated 68Ga-DOTATATE Activity in IgG4-Related Lymphadenopathy

Ga-DOTATATE PET/CT was performed in a 60-year-old man to detect culprit tumor responsible for tumor-induced osteomalacia (TIO). The images revealed multiple foci of abnormal activity in soft tissue lesion, which were not typical of tumor causing TIO in Ga-DOTATATE PET/CT. Considering other neoplastic processes, FDG PET/CT were subsequently performed, which showed all same lesions, although the lesions with highest activity were different between the scans. Pathological examination demonstrated that the patient experienced TIO caused by 1 lesion, but other lesions were due to IgG4-related lymphadenopathy.

Immunoglobulin G4-related kidney disease: Pathogenesis, diagnosis, and treatment

Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized clinical entity that often involves multiple organs; it is characterized by high levels of serum immunoglobulin G4 (IgG4), dense infiltration of IgG4+ cells, and storiform fibrosis. Cellular immunity, particularly T cell-mediated immunity, has been implicated in the pathogenesis of IgG4-RD. The most frequent renal manifestations of IgG4-RD are IgG4-related tubulointerstitial nephritis, membranous glomerulonephropathy (MGN), and obstructive nephropathy secondary to urinary tract obstruction due to IgG4-related retroperitoneal fibrosis, prostatitis, or ureter inflammation. Kidney function impairment can be acute or chronic. In IgG4-MGN, proteinuria can be in the nephrotic range. The diagnosis of IgG4-related kidney disease should not be based solely on serum IgG4 levels or the number of tissue-infiltrating IgG4+ plasma cells. Diagnosis should be based on specific histopathological findings, confirmed by tissue immunostaining and an appropriate clinical context. Steroid treatment is the first-line therapy. For relapsing or refractory cases, immunosuppressants could be combined with steroids. In hydronephrosis patients, appropriate immunosuppressive therapy could preclude the implantation of a double J ureteral catheter.

Neurological Manifestations of IgG4-Related Disease

OPINION STATEMENT

IgG4-related disease (IgG4-RD) is a multisystem inflammatory disorder. Early recognition of IgG4-RD is important to avoid permanent organ dysfunction and disability. Neurological involvement by IgG4-RD is relatively uncommon, but well recognised-hypertrophic pachymeningitis and hypophysitis are the most frequent manifestations. Although the nervous system may be involved in isolation, this more frequently occurs in conjunction with involvement of other systems. Elevated circulating levels of IgG4 are suggestive of the condition, but these are not pathognomonic and exclusion of other inflammatory disorders including vasculitis is required. Wherever possible, a tissue diagnosis should be established. The characteristic histopathological changes include a lymphoplasmacytoid infiltrate, storiform fibrosis and obliterative phlebitis. IgG4-RD typically responds well to treatment with glucocorticoids, although relapse is relatively common and treatment with a steroid-sparing agent or rituximab may be required. Improved understanding of the pathogenesis of IgG4-RD is likely to lead to the development of more specific disease treatments in the future.