CASE PRESENTATION: A 58 year old woman with chief complaint of worsening shortness of breath and dry cough and past medical history of mild diastolic heart failure, hypertension, obesity and obstructive sleep apnea was admitted to the hospital for exacerbation of symptoms. She was hospitalized 6 months prior for similar symptoms when she was diagnosed with COPD exacerbation and was placed on oral steroids which mildly improved her symptoms. Patient is a former smoker of 2.5 packs per day for 30 years. Pulmonary function tests showed lung volumes and diffusion capacities within reference range. Spirometry showed mild restriction with improvement in vital capacity and FEV1 after aerosol treatment, not supporting the sole diagnosis of COPD. Chest CT showed diffuse interlobular septal thickening with upper lobe predominant ground glass attenuation, mild traction bronchiectasis. Imaging also showed pericardial thickening and mild fusiform ectasia of the descending thoracic aorta with mild thickening of the peri-aortic fat. Surgical lung biopsy was performed of the right upper and middle lobe. Results showed histiocytic infiltrates in a lymphangitic pattern with associated fibrosis, as seen with Erdheim Chester disease (ECD). Molecular Markers confirmed BRAF mutation. Nuclear bone scan was subsequently performed and showed scattered areas of abnormal uptake in the maxilla, orbits, tibias, and right forearm consistent with Erdheim-Chester syndrome or polyostotic sclerosing histiocytosis.