Update on Classification, Diagnosis, and Management of Immunoglobulin G4-Related Disease
Immunoglobulin G4-related disease (IgG4-RD) is a chronic fibro-inflammatory autoimmune disorder that has gained increasing recognition worldwide in recent years. Accurate and timely diagnosis, along with appropriate intervention, is crucial for effective management. This article provides a comprehensive update on the classification, diagnosis, and management of IgG4-RD, emphasizing the latest advancements in understanding this complex disease.
Introduction
IgG4-RD was established as a distinct clinical entity in the past decade. It is characterized by significantly elevated serum IgG4 levels and tumefactive lesions. Histopathological features include IgG4-positive lymphoplasmacytic cell infiltrations, storiform fibrosis, obliterative phlebitis, and eosinophil infiltration. Due to its tumor-like presentations, IgG4-RD is often misdiagnosed as malignancy, leading to unnecessary surgeries and significant patient distress. The first international consensus guidance statement on IgG4-RD management was published in 2015, and since then, there has been an exponential growth in research, leading to refined diagnostic criteria and treatment strategies.
Disease Subtypes and Clinical Manifestations
IgG4-RD can affect almost any organ system, with the most common clinical manifestations being tumefactive mass formation and symptoms resulting from adjacent organ compression. For instance, pancreatic-biliary involvement can lead to jaundice, while retroperitoneal fibrosis may cause lower limb edema. Fever is rare, but allergic diseases such as bronchial asthma are common, especially in patients with superficial gland involvement. The 2019 American College of Rheumatology and European League Against Rheumatism (ACR/EULAR) classification criteria identified four clinical phenotypes of IgG4-RD: type 1 (pancreato-hepato-biliary disease), type 2 (retroperitoneal fibrosis and/or aortitis), type 3 (head and neck-limited disease), and type 4 (classic Mikulicz syndrome with systemic involvement).
Organ-Specific Manifestations
IgG4-Related Ophthalmic Disease (IgG4-ROD): IgG4-ROD can involve various orbital structures, including the lacrimal glands, extraocular muscles, and infraorbital nerves. Patients often present with elevated serum IgG4 and IgE levels, increased peripheral eosinophilia, and Th2-associated cytokines. Histopathology typically shows lymphoplasmacytic infiltration and fibrosis, though storiform patterns and obliterative phlebitis are less common.
IgG4-Related Sialoadenitis: This subtype often presents with lower age at onset and longer time to diagnosis compared to other IgG4-RD forms. Patients exhibit higher serum IgG4 levels, IgG4/IgG ratios, and peripheral eosinophil counts. Allergic conditions and multi-organ involvement are more common in these patients.
IgG4-Related Hypophysitis: This condition often has a concealed onset and long disease duration. Panhypopituitarism is the most common symptom. MRI findings include pituitary-stalk enlargement, and while histopathology is definitive, a pituitary biopsy is highly invasive. Diagnostic criteria have been developed to aid in early diagnosis without the need for biopsy.
IgG4-Related Respiratory Disease (IgG4-RRD): IgG4-RRD involves the thorax, including the lung parenchyma, bronchus, mediastinum, and pleura. Chest CT findings include hilar and mediastinal lymphadenopathy, perilymphatic interstitial thickening, and pleural thickening. Bronchoalveolar lavage fluid IgG4 levels are higher in IgG4-RRD compared to pulmonary sarcoidosis, aiding in diagnosis.
IgG4-Related Autoimmune Pancreatitis (Type 1 AIP): Type 1 AIP primarily affects elderly men, with obstructive jaundice being the most common symptom. Radiologic features include diffuse pancreatic swelling, delayed enhancement in the venous phase, and narrowing of the main pancreatic duct. Histopathology shows lymphoplasmacytic infiltration, storiform fibrosis, and obliterative phlebitis, with abundant IgG4-positive plasma cells.
IgG4-Related Sclerosing Cholangitis (IgG4-SC): Most IgG4-SC cases are associated with pancreatic involvement. Serum IgG4/IgG RNA ratio may help differentiate IgG4-SC from primary sclerosing cholangitis (PSC) and malignancies. Cholangiography shows thickened bile duct walls with diffuse or segmental strictures.
IgG4-Related Retroperitoneal Fibrosis (IgG4-RPF) and Periaortitis/Periarteritis: Imaging is crucial for diagnosing IgG4-RPF and periaortitis. CT and MRI reveal retroperitoneal soft tissue distribution around the abdominal aorta and iliac artery. Elevated C-reactive protein (CRP) levels are common in periaortitis.
IgG4-Related Kidney Disease (IgG4-RKD): IgG4-RKD includes IgG4-related tubulointerstitial nephritis (IgG4-TIN) and glomerulonephritis. Patients often present with decreased renal function, mild proteinuria, and hypocomplementemia. Histopathology shows lymphoplasmacytic infiltration and immunoglobulin deposition in the tubular basement membrane.
IgG4-Related Hypertrophic Pachymeningitis (IgG4-RHP): This rare subtype is challenging to diagnose. Serum IgG4 levels are usually normal, but cerebrospinal fluid (CSF) levels are elevated. MRI shows dural thickening or bulging masses. Biopsy remains the gold standard for diagnosis.
Diagnosis
Early diagnosis is critical for effective management. The 2011 comprehensive diagnostic criteria and the 2020 revised version are widely used. The 2019 ACR/EULAR classification criteria emphasize clinical, serologic, radiologic, and pathologic evidence, excluding patients with infrequent organ involvement. Elevated serum IgG4 levels, while not definitive, are a useful screening tool, especially when levels are two to three times the upper limit of normal. Repeated testing is recommended for suspected cases.
Emerging Biomarkers: New biomarkers are being explored for diagnosis, prognosis, and treatment monitoring. Serum IgG2, soluble IL-2 receptor, and chemokine C-C motif ligand 18 are potential indicators of inflammation and fibrosis. Eotaxin-3, identified through proteomics, is a promising biomarker. Hypocomplementemia is particularly relevant in IgG4-TIN. Autoantibodies against Laminin-511-E8, Galectin-3, Annexin-A11, and Prohibitin are potential diagnostic markers. Cellular populations, such as circulating plasmablasts/plasma cells, are also being studied for their role in disease activity and treatment response.
Management
Who Should Be Treated? All patients with active, symptomatic IgG4-RD require treatment. Early intervention is crucial for preventing irreversible organ damage. Asymptomatic patients with single organ involvement may be monitored without immediate treatment.
Glucocorticoid Therapy: Glucocorticoids remain the first-line treatment. The standard dose is 0.6 mg/kg/day, typically starting with 30-40 mg/day of prednisone. Tapering begins after 2-4 weeks, with most patients achieving remission. High-dose glucocorticoids are recommended for severe cases.
Steroid-Sparing Agents: Steroid-sparing agents, such as mycophenolate mofetil (MMF), azathioprine (AZA), and rituximab (RTX), are used for patients with poor response to steroids, frequent relapses, or steroid intolerance. RTX is particularly effective for inducing remission without steroids.
Assessment of Treatment Response: The IgG4-RD Responder Index (IgG4-RD RI) is used to assess disease activity. It evaluates organ involvement and serum IgG4 levels, though subjective factors can influence scoring. Monitoring other biomarkers and imaging changes is also recommended.
Long-Term Maintenance Therapy: Low-dose steroid maintenance therapy is recommended for high-risk patients to prevent relapse. RTX can also be used for maintenance, though the optimal frequency and duration are still under investigation.
Predicting Relapse: Factors influencing relapse include male sex, younger onset, higher serum IgG4 levels, multiple organ involvement, and history of recurrence. Circulating memory B cells are also associated with relapse.
Managing Relapse: Relapsing patients can be retreated with glucocorticoids, and steroid-sparing agents are recommended for maintenance. Most patients achieve remission with resumed glucocorticoid therapy.
Surgical Treatment: Surgery or interventional therapy is considered for severe organ compression or dysfunction. For example, ureteral stenting is used for hydronephrosis, and stent implantation is used for biliary obstruction.
Conclusion
IgG4-RD is a complex and heterogeneous disease that can affect multiple organ systems. Advances in diagnostic criteria, biomarkers, and treatment strategies have improved patient outcomes. Glucocorticoids remain the cornerstone of treatment, but steroid-sparing agents like RTX are increasingly used. Early diagnosis and intervention are crucial for preventing irreversible organ damage. Continued research into the pathogenesis and treatment of IgG4-RD will further enhance our understanding and management of this challenging disease.
doi.org/10.1097/CM9.0000000000001891
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