SESSION TITLE: Diffuse Lung Disease 1 SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/09/2018 01:15 pm - 02:15 pm INTRODUCTION: Langerhans Cell Histiocytosis (LCH) is rare disorder that is characterized by clonal proliferation of infiltrative dendritic cells affecting one or more organs. The incidence of LCH in adults is 2 per million. LCH is associated with wide range of clinical presentations, from localized or ‘single-system disease’ with excellent survival rate to involving 2 or more organs or ‘multisystem disease (MS-LCH)’ with poor prognosis. We report a rare case of MS-LCH in adult. CASE PRESENTATION: A 60-year-old female smoker presented to the pulmonary clinic for abnormal chest CT chest. Her medical work-up was initiated due to low grade fevers, night sweats, diarrhea, persistent productive cough and progressive dyspnea over 3 months. She also reported a recent transient episode of erythematous skin rash that resolved spontaneously. Her CT abdomen showed mass like thickening of sigmoid colon, multiple hepatic lesions and retroperitoneal adenopathy. The FNA of liver mass showed focal steatosis and mild portal fibrosis. Chest CT revealed diffuse thin-walled cysts of various shapes and sizes with associated parenchymal destruction. The cystic lesions were predominant in the upper lungs. Bronchoscopy with TBBx and EBUS-TBNA of mediastinal lymphadenopathy were performed. Histopathology of TBBx revealed histocyte-like mononuclear cells along with eosinophils and lymphocytes, suggestive of LCH. The immunostains of the mononuclear cells were positive for CD1a and S100, confirming the diagnosis of LCH. Flow cytometry from her mediastinal lymph nodes also showed CD1a and S100 positivity. Bone scan showed increase uptake in calvarium, tibia and facial bones suggestive of neoplastic involvement of LCH. With the history, investigation and clinical findings, the diagnosis of MS-LCH was made. Based on the current literature, she was started on intensive combination chemotherapy of vinblastine, prednisone plus 6-mercaptopurine. She continues to improve clinically. DISCUSSION: LCH is a rare neoplasm of Langerhans type cells that is uncommon in adult. MS-LCH is frequently associated with fatal prognosis when there is involvement of risk organs. Therefore, treatment of MS- LCH should be aggressive and longer (12 month). On the other hand, isolated P-LCH has excellent prognosis, and likely to be cured with smoking cessation. Recurrence of LCH has been shown in patient with BrafV600 mutation. Cladribine has been used as 2nd-line treatment in recurrent or resistant cases of all types of LCH. CONCLUSIONS: In summary, LCH should be considered in the differential diagnosis of a patient with unexplained multiorgan disease. Early recognition, diagnosis and treatment are very crucial for the survival, especially in the MS-LCH. Reference #1: Earlam K et al., 2016. Pulmonary Langerhans Cell Histiocytosis and Diabetes Insipidus in a Young Smoker. Can Respir J; 3740902 Reference #2: Lian C et al., 2016. Langerhans Cell Histiocytosis in Adults: A Case Report and Review of the Literature. Oncotarget; 7(14):18678-18683 Reference #3: Tazi A., 2006. Adult Pulmonary Langerhans’s Cell Histiocytosis. Eur Respir J; 27(6):1272-1285 DISCLOSURES: No relevant relationships by Jessita Singh Natasha Albert Messiah Dhas, source=Web Response No relevant relationships by Anna Kyu Chen, source=Web Response No relevant relationships by Sudheer Penupolu, source=Web Response