IgG4-related disease

IgG4-related disease (IgG4-RD) is considered a fibro-inflammatory condition with a marked propensity to form mass forming lesions, characterized by a dense lymphoplasmacytic infiltrate, the presence of abundant IgG4+ plasma cells, frequent elevation of serum IgG4 and a dramatic initial response to glucocorticoid. Nowadays, IgG4-RD has been described in almost every organ system: the pancreatobiliary tract, liver, salivary glands, nasopharynx, bone marrow, lacrimal gland, extra-ocular muscles and retrobulbar space, kidneys, lungs, lymph nodes, meninges, aorta and arteries, skin, breast, prostate, thyroid gland and pericardium. Although the common diagnostic features of all these regional involvements cannot be defined with certainty, and slight differences have been noted in different organs, many histopathological features are shared. Consensus has not yet been reached regarding criteria that have to be fulfilled for a new IgG4-RD. The proposed criteria include appropriate clinical and histopathological findings, presence of abundant tissue-infiltrating IgG4+ plasma cells, high serum IgG4 concentrations, response to steroid therapy, other autoimmune diseases or other organ involvement. The two hallmark features for diagnosis are histopathological characteristics and the presence of infiltrating IgG4+ plasma cells. In this review, we will focus on the histopathological features of IgG4-RD in specific organs and discuss the relationship with inflammatory pseudotumour and malignancy, IgG4 counting methods, and diagnosis using biopsy specimens. IgG4-related disease (IgG4-RD) is a multi-organ system disease that has been recognized in the last 10 years. IgG4-RD has a marked propensity to present as mass-forming lesions. The two hallmark features for diagnosis are histopathological characteristics and the presence of infiltrating IgG4+ plasma cells. Correct identification is crucial to avoid unnecessary major surgical procedures and initiate corticosteroid therapy.     

IgG4-related disease

IgG4-related disease is a recently recognized systemic syndrome characterized by mass-forming lesions, mainly in exocrine tissue, that consist of lymphoplasmacytic infiltrates and sclerosis. There are numerous IgG4+ plasma cells in the affected tissues, and the serum IgG4 level is elevated in these patients. Ocular adnexal IgG4-related disease frequently involves bilateral lacrimal glands, and obliterative phlebitis is rare. Moreover, some malignant lymphomas, especially mucosa-associated lymphoid tissue lymphoma, arise from ocular adnexal IgG4-related disease. It is known that hyper IL-6 syndromes, such as multicentric Castleman's disease, rheumatoid arthritis, and other autoimmune diseases, fulfill the histological diagnostic criteria for IgG4-related disease; therefore, hyper IL-6 syndromes and IgG4-related disease cannot be differentially diagnosed by immunohistochemical staining alone. However, upon laboratory examination, hype IL-6 syndromes show elevation of the CRP level, polyclonal hyper gamma-globulinemia, anemia, and hypoalbuminemia. These findings are quite different from IgG4-related disease, which is not characterized by elevated serum IgA, IgM, and CRP levels. Therefore, laboratory findings are crucial for the differential diagnosis.     

IgG4-related sclerosing disease

IgG4-related sclerosing disease (IgG4-RSD) is a systemic one in which IgG4-positive plasma cells and T lymphocytes extensively infiltrate various organs. The clinical manifestations of the disease include autoimmune pancreatitis, sclerosing cholangitis, cholecystitis, sialodenitis, retroperitoneal fibrosis, tubulointestitial nephritis, interstitial pneumonia, prostatitis, inflammatory pseudotumors and lymphadenopathy, all related with significantly elevated serum IgG4 levels. Tissue fibrosis with obliterative phlebitis of the affected organs is pathologically induced. The disease occurs predominantly in elderly men and responds well to steroid therapy. Since malignant tumors are frequently suspected on initial presentation, IgG4-RSD should be considered in the differential diagnosis to avoid unnecessary surgery.     

IgG4-related kidney disease

IgG4-related disease (IgG4-RD) is a recently recognized systemic immune-mediated disease that can affect nearly any organ or tissue. The most common manifestation in the kidney is IgG4-related tubulointerstitial nephritis (IgG4-TIN), which can present as renal insufficiency, renal mass lesions, or both. Histologically, IgG4-TIN is a plasma cell-rich interstitial inflammatory infiltrate with mononuclear cells, eosinophils, and increased IgG4+ plasma cells, along with expansile interstitial fibrosis that often has a “storiform” appearance. Tubular basement membrane immune complex deposits, best visualized on immunofluorescence staining, are present in most cases. IgG4-TIN usually shows a rapid response to steroid therapy. Glomeruli may be affected by IgG4-RD, usually in the form of membranous glomerulonephritis; other glomerular lesions have also been described. This review describes the different histopathologic patterns of renal involvement by IgG4-RD, with associated clinical, radiographic, and serologic features.     

Immunology of IgG4-related disease

Immunoglobulin G4-related disease (IgG4-RD) is a fibroinflammatory condition that derives its name from the characteristic finding of abundant IgG4⁺ plasma cells in affected tissues, as well as the presence of elevated serum IgG4 concentrations in many patients. In contrast to fibrotic disorders, such as systemic sclerosis or idiopathic pulmonary fibrosis in which the tissues fibrosis has remained largely intractable to treatment, many IgG4-RD patients appear to have a condition in which the collagen deposition is reversible. The mechanisms underlying this peculiar feature remain unknown, but the remarkable efficacy of B cell depletion in these patients supports an important pathogenic role of B cell/T cell collaboration. In particular, aberrant T helper type 2 (Th2)/regulatory T cells sustained by putative autoreactive B cells have been proposed to drive collagen deposition through the production of profibrotic cytokines, but definitive demonstrations of this hypothesis are lacking. Indeed, a number of unsolved questions need to be addressed in order to fully understand the pathogenesis of IgG4-RD. These include the identification of an antigenic trigger(s), the implications (if any) of IgG4 antibodies for pathophysiology and the precise immunological mechanisms leading to fibrosis. Recent investigations have also raised the possibility that innate immunity might precede adaptive immunity, thus further complicating the pathological scenario. Here, we aim to review the most recent insights on the immunology of IgG4-RD, focusing on the relative contribution of innate and adaptive immune responses to the full pathological phenotype of this fibrotic condition. Clinical, histological and therapeutic features are also addressed.     

General principles of IgG4-related disease

The concept of IgG4-related disease is rapidly evolving. The disease has been described in virtually every organ system and can mimic a number of other important malignant and inflammatory conditions. Consensus on nomenclature was proposed at an international IgG4-related disease symposium in Boston in 2011. Diagnostic criteria have been established to include characteristic histopathology, clinical and radiological manifestations, serology and response to treatment. Consensus histopathology guidelines have been agreed by an international panel of experts. Treatment options continue to expand and include corticosteroids, immunosuppressive therapy and B-cell depletion strategies. The role of IgG4 in pathogenesis remains uncertain but elucidating this will be crucial in the further understanding of this disease. This review will summarize the principles of IgG4-related disease from a clinical perspective.     

Cutaneous multicentric Castleman's disease mimicking IgG4-related disease

Castleman's disease, an uncommon lymphoproliferative disorder, can be difficult to differentiate from immunoglobulin (Ig) G4-related disease. The latter is typically characterized by elevated serum IgG4 levels and abundant IgG4-positive cells. However, multicentric Castleman's disease can also have elevated serum IgG4 levels and even fulfill the histological diagnostic criteria for IgG4-related disease. We present a case of cutaneous multicentric Castleman's disease mimicking IgG4-related disease. A 55-year-old Japanese woman developed erythematous and brown plaques on her back. Skin biopsy revealed regressive follicles with interfollicular plasmacytosis, and many plasma cells were positive for IgG4 (mean 263.67 ± 79.19, range 214–355 per high power field). The IgG4-/IgG-positive cell ratios were 35.6%, 36.2%, and 48.4%, respectively, with an average of 40.6%, thus fulfilling the histological diagnostic criteria for IgG4-related disease. Furthermore, serum IgG4 level was significantly elevated (1490 mg/dl; normal range: 4.8–105 mg/dl). However, laboratory findings of anemia, hypoalbuminemia, polyclonal gammaglobulinemia, high C-reactive protein level, and elevated serum interleukin-6 level were consistent with hyper-IL-6 syndrome. Hence, the diagnosis of cutaneous multicentric Castleman's disease was made. In conclusion, IgG4-related disease cannot be differentiated from hyper-IL-6 syndromes on histology alone. Instead, laboratory analyses are necessary to distinguish between the two diseases.     

The clinical spectrum of IgG4-related disease

IgG4-related disease (IgG4-RD) is an emerging immune-mediated disease with the capability of involving essentially any organ. The epidemiology of this disease has not been explored in detail. A majority of patients reported in the literature to date are from Japan, but the condition has been described all across the world and there is no strong evidence to suggest a predilection for Asian populations. The mean age at diagnosis is approximately 60 years and there is a decided male predominance for many clinical features, with an overall male:female ratio of 8:3. A cardinal feature of IgG4-RD is single or multiple organ swelling that often raises concern for malignancy. IgG4-RD should be suspected in patients presenting with unexplained enlargement or swelling of one or more organs. Presenting features vary substantially according to the specialty to which patients present first; in addition, the disease can be diagnosed unexpectedly in pathological specimens or identified incidentally on radiology studies. Involvement of major organs is common and IgG4-RD may lead to organ failure, particularly in the pancreas, liver and biliary tree, kidneys, thyroid gland, lungs, and aorta. The diagnosis of IgG4-RD relies on the coexistence of various clinical, laboratory and histopathological findings, although none is pathognomonic by itself.     

Characteristic tubulointerstitial nephritis in IgG4-related disease

Nephropathy associated with IgG4-related disease is characterized by tubulointerstitial nephritis. To better identify its pathology, the present study analyzed clinicopathologic features of IgG4-related tubulointerstitial nephritis cases from across Japan. Sixteen cases were identified as IgG4-related nephropathy using the criterion of high serum IgG4 levels (>135 mg/dL) with abnormal kidney computed tomography or elevated serum creatinine levels. Male predominance (75%) and advanced age (average, 62.0 years) were noted. Eight cases displayed no autoimmune pancreatitis. Renal computed tomography abnormalities were found in 12 of 13 cases examined. Renal dysfunction was found in 15 of 16 cases at biopsy. Distinctive features of tubulointerstitial lesions included (1) well-demarcated borders between involved and uninvolved areas; (2) involvement of the cortex and medulla, often extending beyond the renal capsule and with occasional extension to retroperitoneal fibrosis; (3) interstitial inflammatory cells comprising predominantly plasma cells and lymphocytes, with a high prevalence of IgG4-positive cells often admixed with fibrosis; (4) peculiar features of interstitial fibrosis resembling a "bird's-eye" pattern comprising fibrosis among inter-plasma cell spaces; and (5) deposits visible by light and immunofluorescent microscopy in the tubular basement membrane, Bowman capsule, and interstitium that are restricted to the involved portion, sparing normal parts. Ultrastructural analysis revealed the presence of myofibroblasts with intracellular/pericellular collagen accompanied by plasma cell accumulation from an early stage. Histology could not discriminate between IgG4-related tubulointerstitial nephritis with and without autoimmune pancreatitis. In conclusion, the distinctive histologic features of IgG4-related tubulointerstitial nephritis can facilitate the differential diagnosis of tubulointerstitial nephritis, even without autoimmune pancreatitis or an abnormal computed tomography suggesting a renal tumor.     

IgG4-related prostatitis progressed from localized IgG4-related lymphadenopathy

Immunoglobulin G4-related disease (IgG4-RD) is a recently described inflammatory disease involving multiple organs. Prostate involvement with IgG4-RD is very rare. In this report, we describe a case of IgG4-related prostatitis progressed from localized IgG4-related lymphadenopathy. This patient was present with urine retention symptoms. MRI and CT examination revealed the prostatic enlargement and the multiple lymphadenopathy. Serum IgG4 levels were elevated. Prostatic tissue samples resected both this time and less than 1 year earlier showed the same histological type of prostatitis with histopathologic and immunohistochemical findings characteristic of IgG4-RD. The right submandibular lymph nodes excised 2 years earlier were eventually proven to be follicular hyperplasia-type IgG4-related lymphadenopathy. This is the first case of IgG4-RD that began as localized IgG4-related lymphadenopathy and progressed into a systemic disease involving prostate and multiple lymph nodes. This patient showed a good response to steroid therapy. This leads us to advocate a novel pathogenesis of prostatitis, and a novel therapeutic approach against prostatitis. Pathologists and urologists should consider this disease entity in the patients with elevated serum IgG4 levels and the symptoms of prostatic hyperplasia to avoid ineffective medical or unnecessary surgical treatment.     

IgG4-related lymphadenopathy and IgG4-related lymphoma: moving targets

IgG4 is the least common of all the IgG subclasses. In recent years an uncommon systemic disease characterized by variable manifestations that may include the presence of tumour-like sclerosing lesions in a variety of extranodal sites, lymphadenopathy, presence of increased numbers of IgG4+ plasma cells in affected tissues, elevated serum IgG4 level, frequent presence of autoantibodies and often, a good response to steroid therapy or Rituximab has been described. The disorder has been called IgG4-related sclerosing disease, IgG4-related systemic disease and IgG4-related autoimmune disease; currently the preferred designation is IgG4-related disease (IgG4-RD). In addition to other changes that may be found in association with IgG4-RD, some investigators have suggested that IgG4-RD may serve as a substrate for the development of lymphoma.This review focuses on lymphadenopathy associated with IgG4-RD and also explores the significance of isolated lymphadenopathy with increased numbers of IgG4+ plasma cells. Emerging data on lymphomas arising in association with IgG4-RD and the possibility of an increased risk of lymphoma in patients with IgG4-RD are also discussed.     

IgG4相关性疾病临床病理学特征分析

目的：探讨IgG4相关性疾病的病理学形态、免疫表型特征。方法观察12例IgG4相关性疾病的镜下特点,结合免疫组化EnVision两步法染色检测IgG、IgG4、CD138、CD34的表达,分析IgG4相关性疾病的病理学形态特征。结果 IgG4相关性疾病主要表现为组织弥漫性纤维化;伴大量淋巴细胞、浆细胞浸润,围绕血管神经分布;闭塞性静脉炎形成,免疫组化EnVision两步法染色IgG4阳性浆细胞与IgG阳性浆细胞比例>40%。结论 IgG4相关性疾病临床特点和影像学无特异性,易误诊为肿瘤,术前血清IgG4检测可作为疑似病例的首选方法。     

Sudden coronary death due to IgG4-related disease

A 54-year-old male entered the emergency room in cardiorespiratory arrest after syncope at home. Resuscitation was attempted, but the patient died a few hours later. At necropsy, aneurysms were found at the right and left anterior descending coronary arteries. At microscopic examination, there was no significant coronary atherosclerosis, and a dense inflammatory infiltrate was detected, with a high number of igG4-positive cells (94.0 positive cells/hpf). The case illustrates that IgG4-related disease can cause coronary disease and sudden cardiac death.