IgG4-related lung disease and seropositive undifferentiated arthritis in a patient initially presenting with monoarthritis: a case report

Abstract

Abstract Background IgG4-related lung disease (IgG4-RLD) is a fibroinflammatory pulmonary manifestation of IgG4-related disease (IgG4-RD). Its comorbidity with seropositive undifferentiated arthritis (SUA) is rare and may be overlooked due to overlapping clinical and immunological features. Case presentation A 71-year-old man with acute left knee pain secondary to a meniscal tear with synovitis, as confirmed by MRI, was scheduled for arthroscopy. A preoperative chest radiograph incidentally revealed diffuse right lung lesions. Diagnostic workup and therapeutic strategy Laboratory studies showed elevated rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies. The first multidisciplinary team (MDT) discussion established a diagnosis of SUA and initiated disease-modifying antirheumatic drug (DMARD) therapy, which resolved the arthralgia but did not improve the lung lesions. A subsequent MDT review, incorporating chest CT findings (thickened bronchovascular bundles and consolidation) and lung biopsy results, confirmed the diagnosis of IgG4-RLD. Treatment was then adjusted to high-dose glucocorticoids combined with DMARDs. Both pulmonary and articular manifestations showed significant remission. Conclusion This rare case of IgG4-RLD complicating SUA highlights the importance of considering IgG4-RLD in patients with seropositive inflammatory arthritis presenting with atypical pulmonary imaging findings, particularly when lung lesions fail to respond to conventional DMARD therapy. MDT collaboration is essential for accurate diagnosis and optimal management of these concomitant autoimmune conditions.