Pseudotumoral Lesion of the Lacrimal Sac Unveiling Seronegative IgG4-Related Disease: A Diagnostic Challenge.

Introduction: This case report details a pseudotumoral lesion of the lacrimal sac, serving as the initial manifestation of seronegative IgG4 disease. Case Presentation: A 36-year-old female, without notable medical history, presented with a swelling located near the inner canthus and lacrimal crest associated with pain and skin redness. Despite two rounds of antibiotics, there was no improvement. Initially diagnosed as chronic dacryocystitis, antibiotic therapy with amoxicillin clavulanate was continued, and an orbital MRI was conducted for further evaluation. The MRI revealed a fibrous tissue process adjacent to the lacrimal sac, raising suspicion of malignancy. A biopsy under general anesthesia was performed due to a strong suspicion of squamous cell carcinoma of the sac. Biopsy revealed lymphoplasmacytic infiltration and storiform fibrosis, meeting ACR/EULAR criteria for IgG4 disease. Internal medicine evaluation found no extralacrimal organ involvement, and serum IgG levels were normal. Diagnostic criteria, including clinical presentation, imaging review, histological features, and exclusion criteria, confirmed IgG4 disease and ruled out malignancy. Systemic corticosteroid therapy resulted in rapid clinical improvement, supporting the diagnosis. Conclusion: This case underscores the diagnostic challenges of IgG4 disease, emphasizing the importance of a comprehensive approach, including histological confirmation. Distinguishing it from malignancies is crucial, and biopsy should be considered in cases of diagnostic uncertainty before invasive or systemic treatments for suspected tumors.