Progressive Unilateral Cavitary Lung Disease With Nondiagnostic Bronchoalveolar Lavage Flow Cytometry Mimicking Sarcoidosis: A Case Report

Bronchoalveolar lavage (BAL) cellular analysis is frequently used as an adjunct in the evaluation of interstitial lung disease (ILD), including sarcoidosis. Findings such as lymphocyte fraction and CD4/CD8 ratio may be supportive in the appropriate context but are neither specific nor diagnostic. We report the case of a 41‑year‑old woman with progressive unilateral cavitary lung disease and mediastinal lymphadenopathy initially raising concern for sarcoidosis. BAL flow cytometry from the affected lung was non‑diagnostic due to poor cell viability and near absence of T‑cell populations. Serial computed tomography (CT) imaging demonstrated features atypical for sarcoidosis, including bronchial cutoff, cavitation, and contralateral pulmonary nodules. This case highlights the limitations of BAL flow cytometry and reinforces the importance of multidisciplinary diagnostic integration in complex pulmonary disease.