SESSION TITLE: Lung Pathology 3 SESSION TYPE: Affiliate Case Report Poster PRESENTED ON: Tuesday, October 31, 2017 at 01:30 PM - 02:30 PM INTRODUCTION: IgG4 related disease is a recently identified entity that causes tumefactive lesions of organs due to lymphoplasmacytic infiltration by IgG4 positive plasma cells and leads to fibrosis. We present a young man with history of recurrent cryptogenic organizing pneumonia (COP) diagnosed retrospectively as inflammatory pseudotumor of the lung, after calvarial and meningeal plasma cell granuloma (PCG) diagnosis, both metachronous manifestations of IgG4 related disease. CASE PRESENTATION: A 28-year-old male presented to our hospital with seizures in 2016. MRI showed parietal and occipital calvarial lesions with meningeal enhancement that were resected. Biopsy showed spindle cell proliferation with mature polyclonal plasma cells and absence of ALK1 staining, consistent with PCG. IgG4 staining was positive. Computerized tomographic scan revealed chronic interstitial fibrotic changes in bilateral lung apices. On retrospective chart review, it was noted that he had presented with cough with interstitial infiltrates/fibrosis, fever and leukocytosis in 2014. At that time, an extensive infectious and connective tissue disease work up was negative and bone marrow aspiration and biopsy were normal. He was empirically treated with prednisone with subsequent resolution of symptoms. Earlier in 2009, he had presented to another hospital with fever and interstitial lung infiltrates and was treated as COP after lung biopsy. Reevaluation of the slides from 2009 biopsy was consistent with inflammatory pseudotumor of the organizing pneumonia, fibrohistiocytic type with predominant macrophages and fibrosis. DISCUSSION: Autoimmune pancreatitis was the first IgG4 disease to be characterized; however it can involve any organ. Organ involvement can be metachronous. Histopathological features of IgG4 related disease are dense lymphoplasmacytic infiltrate, storiform fibrosis and obliterative phlebitis. There is variability in findings in organs such as the lungs in which aggregates of neutrophils may be found within inflammatory infiltrates, with lack of storiform fibrosis in non-solid lesions such as interstitial pneumonia. Steroids are the first line of treatment, however patients may flare despite adequate treatment. Immunosuppressive drugs have been used as steroid-sparing agents and for maintenance therapy. Steroid-refractory disease and recurrent disease has been shown to have a good response to rituximab. Response to treatment is better during the lymphoplasmacytic infiltration stage, prior to extensive fibrosis. CONCLUSIONS: It is important to consider IgG4 related disease in tumors of any organ and if tissue biopsy is consistent with this diagnosis, extensive surgery can be avoided since the disease in the active phase responds to steroid or rituximab. Reference #1: “Inflammatory myofibroblastic tumor (plasma cell granuloma). Clinicopathologic study of 20 cases with immunohistochemical and ultrastructural observations.” Am J Clin Pathol 94(5): 538-546. DISCLOSURE: The following authors have nothing to disclose: Aditya Kotecha, Hussein Saleh, Saraschandra Vallabhajosyula, Christina Desousa, AbuFazl Mohammed, Vivek Iyer, Geetha Krishnamoorthy No Product/Research Disclosure Information