Snapshot A 56-year-old man presents for a follow up with his primary care physician for a few weeks of low-grade fevers, cough, malaise, and shortness of breath. He had tested negative for tuberculosis and his sputum cultures had shown no growth. His symptoms have not responded to a course of azithromycin. His past medical history includes hypertension, for which he is taking hydrochlorothiazide. He has no history of autoimmune diseases. He currently works as a software engineer. On physical exam, there are sparse inspiratory crackles bilaterally. A chest radiograph shows bilateral patchy infiltrates, and he is sent for a high-resolution computed tomography. Introduction Clinical definition cryptogenic organizing pneumonia (COP) is a rare organizing noninfectious pneumonia/bronchiolitis in which the cause is often unknown may be caused by chronic inflammatory diseases or medications previously known as bronchiolitis obliterans organizing pneumonia (BOOP) Epidemiology Incidence rare Demographics adults Risk factors chronic inflammatory diseases rheumatoid arthritis other connective tissue diseases medications amiodarone ETIOLOGY Pathogenesis inflammation of the small airways (bronchioles) with chronic alveolitis exact pathogenesis is unknown but thought to be related to alveolar injury and fibrotic alveolar bud formation Presentation Symptoms systemic symptoms fever malaise myalgia cough shortness of breath Physical exam respiratory rales inspiratory crackles Imaging Chest radiography findings bilateral patchy infiltrates Chest computed tomography (CT) findings patchy and migratory ground-glass opacities alveolitis Studies Sputum and blood cultures negative Transbronchial biopsy or video-assisted thoracoscopy histology endoluminal buds of granulation tissue and connective tissue Masson body that plugs the small airways obliterated airways Differential Pneumoconioses (e.g., asbestosis) distinguishing factor typically does not present with systemic symptoms presents with a more chronic course typically has a clear occupational exposure does not respond to steroids DIAGNOSIS Making the diagnosis based on clinical presentation and studies definitive diagnosis via biopsy results Treatment Management approach COP does not respond to antibiotics First-line steroids Complications Relapse of disease Respiratory failure rare Prognosis Typically very good with treatment