Abstract Introduction Immunoglobulin G4-related disease (IgG4-RD) is a systemic, immune-mediated fibro-inflammatory disorder with diverse clinical manifestations. When it presents with isolated respiratory symptoms, it can often be misdiagnosed as refractory asthma. The treatment of multisystemic, glucocorticoid-dependent disease becomes complicated due to the cumulative toxicity of corticosteroids, necessitating the need for heightened awareness of IgG4-RD diagnosis and the adoption of steroid-sparing therapeutic strategies. Case Presentation A 70-year-old male with a significant history of coronary artery disease and two prior percutaneous coronary interventions presented with progressive dyspnea and recurrent wheezing over the past three years. Initial laboratory findings showed elevated eosinophil count and IgE levels, leading to a diagnosis of asthma. Further investigations revealed a systemic illness characterized by leukopenia, thrombocytopenia, polyclonal hypergammaglobulinemia, hypocomplementemia, and markedly elevated serum IgG4 levels. Imaging studies showed mediastinal and cervical lymphadenopathy, bilateral pulmonary infiltrates with fibrotic changes, and evidence of cardiac conduction system involvement. Histopathological examination of both a lung biopsy and cervical lymph node biopsy revealed dense lymphoplasmacytic infiltration, storiform fibrosis, and an increased number of IgG4-positive plasma cells, with an IgG4/IgG ratio exceeding 40%, confirming the diagnosis of IgG4-RD. Although the disease showed a strong response to glucocorticoids, the patient developed severe iatrogenic complications, including bilateral avascular necrosis of the femoral heads and secondary adrenal insufficiency, with clinical and radiological progression upon tapering of corticosteroids. Discussion According to the 2019 ACR/EULAR Classification Criteria, the patient was definitively diagnosed with multisystemic IgG4-RD. Due to glucocorticoid dependency and significant treatment-related morbidity, the treatment was switched to rituximab to induce a steroid-free remission. This case highlights that IgG4-RD can present as a severe multisystemic disease, with dominant respiratory symptoms that may be mistaken for refractory asthma. It underscores the critical importance of systemic evaluation in such patients. For those with complex, steroid-dependent disease who experience unacceptable toxicity from corticosteroids, B-cell depletion therapy represents a pivotal treatment strategy to achieve disease control and mitigate long-term corticosteroid-related sequelae. This abstract is funded by: None
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