Immune Alveolitis Profile In Bronchoalveolar Lavage Of Infiltrative Lung Diseases: Not Just Counting Matters

Background: Bronchoalveolar lavage (BAL) is a major diagnostic tool in infiltrative lung diseases (ILD). Reports of its findings mainly focus on cell differential ratio. However, cellular morphological features provide additional valuable information. We defined an \"immune alveolitis\" cytological profile, characterized by lymphocytic alveolitis with activated lymphocytes, and macrophages in epithelioid transformation or foamy macrophages desquamating in cohesive clusters with lymphocytes. Its significance in ILD is unknown. Aims and Objectives: To describe patients’ characteristics and diagnoses associated with an immune alveolitis profile in undiagnosed ILD. Methods: We performed a retrospective observational study at Nantes University Hospital, France. Eligible patients were adults undergoing diagnostic exploration for ILD, whose BAL fluid displayed an immune alveolitis profile suggested by the pathologist. For each patient, we collected clinical, radiological and biological characteristics as well as the final etiology of ILD. Results: Between January 2012 and December 2018, 249 patients were included. Mean age was 57±16 years, 140 patients (56%) were men and 163 (65%) were immunocompromised. Ground glass opacities were the most frequent lesions on CT scan (79%). BAL cellularity was high with marked lymphocytosis (51±18%). The most frequent etiological diagnoses were pneumocystis pneumonia (24%), drug-induced pneumonia (20%), viral pneumonia (14%) and hypersensitivity pneumonitis (10%). Conclusions: Our study highlights the additional value of BAL qualitative description in ILD. We suggest incorporating the immune alveolitis profile for the diagnosis and management of ILD.