Challenges in Diagnosing and Differentiating IgG4-Related Disease From Sjögren’s Disease: A Case Report and Literature Review

IgG4-related disease (IgG4-RD) is a multi-organ fibroinflammatory condition often misdiagnosed due to its clinical similarities with other rheumatologic diseases such as Sjögren's syndrome (SS) and malignancy. This case highlights a 76-year-old woman with a complex medical history who presented with symptoms initially suggestive of SS but was ultimately diagnosed with IgG4-RD. The patient in our case report presented with bilateral, large, nontender submandibular lymphadenopathy. Initial serological tests were negative for SSA and SSB markers but revealed elevated immunoglobulin G levels of 2811 mg/dL. Imaging showed enlarged submandibular glands and lymphadenopathy. A core biopsy revealed a dense nodular lymphocytic infiltrate with variable parenchymal fibrosis and salivary gland acinar atrophy. The specimen was sent for further immunohistochemistry (IHC) testing as extended lab workup showed IgG4 levels of 843 mg/dL, raising concern for underlying IgG4-RD. IHC showed an increased number of IgG4 plasma cells, up to 50% in some areas, confirming the diagnosis of IgG4-RD. Treatment with prednisone led to rapid symptomatic improvement. Differentiating IgG4-RD from SS is challenging due to overlapping clinical and histological features. Elevated serum IgG4 levels (>135 mg/dL) are suggestive but not definitive for IgG4-RD; biopsy remains the gold standard for diagnosis. This case underscores the importance of considering IgG4-RD in patients presenting with SS-like symptoms, especially in the absence of anti-Ro/SSA and anti-La/SSB antibodies, and of initiating an extensive workup to fully delineate the extent of the disease in order to initiate timely treatment and prevent organ damage. This case report emphasizes the need for thorough evaluation in patients with SS-like symptoms to differentiate IgG4-RD, ensuring accurate diagnosis and effective treatment. Prompt recognition and management of IgG4-RD can improve patient outcomes and prevent long-term morbidity.