[Bronchoalveolar lavage in hairy cell leukemia with pulmonary infiltration].

We report a 78-year-old male patient suffering from hairy cell leukemia, presenting clinically mainly with dyspnea. Radiology exhibited bilateral ground-glass shadows. In order to prevent pneumonia as a possible side effect due to conventional chemotherapy, it was decided to first treat the patient with rituximab; however, dyspnea persisted. Therefore, bronchoscopy was performed and specimens were sampled for both histological examination and bronchoalveolar lavage (BAL) analysis. BAL showed lymphocytosis (28.7%), and by means of immunocytochemistry a few CD79a+ B‑lymphocytes as well as lymphoid cells positive for the hairy cell marker DBA44 were observed. In addition, molecular study revealed the BRAF V600E mutation. Thus, the findings of BAL were interpreted as lung infiltration by hairy cell leukemia. This result was confirmed by histology. Following a therapy switch to cladribine, a significant improvement was reached. Pulmonary infiltrates by hairy cell leukemia were rarely described. This case represents the first report of hairy cell leukemia diagnosed by means of BAL. It may be difficult to clearly separate between lymphoma infiltration of the lung and medicamentous pneumonitis, but this differential diagnosis can be supported by morphological methods.