A43-06 A Diagnostic Masquerade: Bronchiolitis Obliterans Organizing Pneumonia Presenting as Non-Resolving Pneumonitis

Abstract Introduction Bronchiolitis obliterans organizing pneumonia (BOOP), also referred to as cryptogenic organizing pneumonia when idiopathic, is a rare non-infectious inflammatory lung disease characterized by intraluminal fibroblastic plugs within alveolar ducts and bronchioles. Despite distinct histology, its nonspecific features often mimic other diseases, leading to misdiagnosis. In the absence of known triggers such as infection, drug toxicity, or connective tissue disease, idiopathic BOOP in an otherwise healthy adult represents an uncommon and diagnostically challenging presentation. Case Report A 51-year-old previously healthy male presented with a 2.5-week history of worsening dry cough, dyspnea, fatigue, myalgias, and unintentional weight loss. He denied fever or recent infections. His occupational history was notable for chronic dust and fume exposure as a construction manager, and he smoked half a pack of cigarettes daily.On arrival, he was afebrile but tachycardic (96 beats per minute) and mildly hypertensive (156/99 mmHg), with oxygen saturation of 95% on room air. Laboratory evaluation revealed leukocytosis (white blood cell count 13.0 × 109/L), normocytic anemia (hemoglobin 12.5 g/dL), and markedly elevated inflammatory markers (CRP 142.3 mg/L and ESR 96 mm/hr). Chest radiography demonstrated bilateral punctate opacities, and high-resolution computed tomography (HRCT) showed diffuse centrilobular nodules without consolidation or lymphadenopathy—findings concerning for miliary tuberculosis or vasculitis.He was empirically treated with broad-spectrum antibiotics and placed under airborne isolation for possible tuberculosis (TB). Interferon-gamma release assay (IGRA) was negative, and acid-fast bacilli (AFB) testing was nondiagnostic. Bronchoscopy with transbronchial biopsy revealed intra-alveolar fibroblastic plugs (Masson bodies) and chronic interstitial inflammation, diagnostic of BOOP. No granulomas or infectious organisms were identified.The patient was started on oral prednisone, with rapid symptomatic improvement and complete radiographic resolution on follow-up imaging. He remains asymptomatic six months later on a tapering steroid regimen. Discussion This case illustrates a rare presentation of idiopathic BOOP masquerading as miliary TB in an immunocompetent host. The combination of diffuse nodular infiltrates and systemic symptoms initially directed evaluation toward infectious etiologies, delaying definitive diagnosis. The absence of known precipitating factors highlights its cryptogenic nature and underscores the diagnostic value of histopathologic confirmation in non-resolving pneumonitis.BOOP is an underrecognized, steroid-responsive interstitial lung disease where early treatment prevents irreversible fibrosis. This case emphasizes the need for heightened clinical suspicion for organizing pneumonia in atypical radiologic presentations, even among healthy adults, reinforcing the importance of multidisciplinary evaluation in rare pulmonary pathologies. This abstract is funded by: None