A40-11 Expanding the Radiologic Spectrum of Adult Pulmonary Langerhans Cell Histiocytosis: Alveolar Consolidation and Cavitary Disease

Abstract Introduction Pulmonary Langerhans Cell Histiocytosis (PLCH) is a rare interstitial lung disease, representing about 3% of all diffuse parenchymal lung disorders. It can present either as part of multisystem Langerhans cell histiocytosis or as an isolated pulmonary condition, most commonly affecting young adult smokers. Diagnosis relies on characteristic clinical, radiologic, and histopathologic features. While alveolar consolidation is uncommon and usually reported in pediatric cases, we present an atypical adult case of PLCH with diffuse pulmonary involvement, and large cavitation. Case Report A 64-year-old former male smoker with medical history significant for chronic obstructive pulmonary disease presented for progressive shortness of breath and fatigue. He denied fever, significant cough, or chest pain. Over the preceding four years, multiple CT scans demonstrated persistent pulmonary nodules and airspace diseases. High-resolution CT revealed innumerable bilateral hazy nodules, emphysema, diffuse bronchial thickening, right-sided subpleural consolidation, and a 5 cm right apical air-containing cavity with mild mediastinal shift. An extensive infectious and malignancy workup including bacterial, fungal, mycobacterial, and Aspergillus studies were unremarkable. Bronchoscopy did not demonstrate endobronchial lesion and BAL cultures were negative. A video-assisted thoracoscopic biopsy revealed Langerhans cell histiocytosis, positive for S100 and CD68, with associated fibrosis, smoking-related changes, and focal noncaseating granulomas; AFB and fungal stains were negative. Given the absence of infection or malignancy, findings were attributed to atypical progression of Pulmonary Langerhans Cell Histiocytosis. The patient initially was started on corticosteroids that were discontinued due to steroid-induced hyperglycemia, was maintained on cytarabine therapy, and was counseled on strict smoking cessation. Discussion This case demonstrates atypical diffuse pulmonary involvement with an unusual combination of alveolar consolidation, large cavitation, and diffuse bilateral nodularity. Alveolar consolidation is rarely described in adult PLCH, with only one known prior case reported, though it may occur in up to one-third of pediatric cases. The 5 cm cavitation and hazy nodules closely mimicked infectious or malignant disease; however, extensive infectious and malignancy evaluations were negative, supporting atypical fibrosing progression of PLCH. These findings broaden the recognized radiologic spectrum of PLCH and highlight the importance of including it in the differential diagnosis of chronic interstitial and cavitary lung disease. This abstract is funded by: None