en Reumatology Reumatology case report case report <span style="font-size:14px;"><span style="font-family:Times New Roman;"><span style="color:#0000ff;"><strong><em>Background</em></strong><em>:</em></span> IgG4-related disease is a newly recognized fibroinflammatory disease presenting with multiple features including mass forming lesion; a dense lymphoplasmacytic infiltrate; a characteristic histopathological appearance and often elevated serum of IgG4. This disease can potentially affect any organ and interestingly, the affected organs share common histopathological features including a dense lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells, storiform fibrosis, and mild to moderate eosinophilia<br> <span style="color:#0000ff;"><strong><em>Case Presentation:</em></strong></span> A&nbsp;45-year-old&nbsp;man presented complaining of proptosis and gradual decrease in visual acuity of right eye. He had undergone many work-ups but without any definitive diagnosis. Through a combination of clinical and para-clinical investigations, the diagnosis of IgG4-RD was established. 693 mg/dL). Aggressive treatment (pulse of cyclophosphamide and pulse of corticosteroid) was started hoping to save the patient&rsquo;s vision. Two weeks following the treatment, there was improvement with his visual acuity and proptosis.<br> <span style="color:#0000ff;"><strong><em>Conclusion</em></strong><em>:</em></span> In any patient with chronic tumor like lesions and pseudotumors without the evidence of malignancy, we should think of IgG4-related disease. In this circumstance, biopsy may lead us to the definitive diagnosis. Early diagnosis and treatment of IgG4-RD may inhibit further irreversible organ damages.</span></span> IgG4-related disease, IgG4-related orbitopathy, visual acuity, Proptosis. 127 131 http://caspjim.com/browse.php?a_code=A-10-1402-3&slc_lang=en&sid=1 Samaneh Azizianesh sam.medicin84@gmail.com 100319475328460033359 100319475328460033359 No Research Center for Rheumatologic Diseases, Amir-Alam Hospital, Tehran University of Medical Sciences, Tehran, Iran Fatema Rizvi fateme.sadaat1@gmail.com 100319475328460033360 100319475328460033360 No School of medicine, Tehran University of Medical Science, Tehran, Iran Hamed Zainaldain Hamed.hadi@aol.com 100319475328460033361 100319475328460033361 No School of medicine, Tehran University of Medical Science, Tehran, Iran Samira Alesaeidi ahmad.23088@gmail.com 100319475328460033362 100319475328460033362 Yes Department of Rheumatology, Amir-Alam Hospital, Tehran, Iran