Q: Patient is admitted to ICU with fever, malaise and cough. High resolution CT scan (HRCT) is performed and bronchoalveolar lavage (BAL) is performed. Result of BAL is c/w mixed cellularity with more lymphocytes, some neutrophils and some eosinophils. "Mixed pattern" of increased cellularity is characteristic of which disease process?


Answer: Cryptogenic organizing pneumonia (COP)

BAL in COP is performed more to rule out other pulmonary disease processes. If bronchoscopy remains without specific findings and BAL shows 'mixed cellularity", it points more towards COP. Patients with COP usually have higher lymphocyte counts than those with idiopathic pulmonary fibrosis (IPF), but similar in proportion to hypersensitivity pneumonitis. BAL may also shows foamy macrophages, mast cells and plasma cells.



References:

1. Katzenstein AL, Myers JL, Prophet WD, et al. Bronchiolitis obliterans and usual interstitial pneumonia. A comparative clinicopathologic study. Am J Surg Pathol 1986; 10:373. 

2. Colby, TV, Myers, JL. The clinical and histologic spectrum of bronchiolitis obliterans including bronchiolitis obliterans organizing pneumonia (BOOP). Semin Respir Med 1992; 13:119.