Pulmonary complications are common in patients with myelodysplastic syndrome (MDS) and may be caused by infections, heart failure, hemorrhage, chemotherapy and rarely by leukemic infiltration of the parenchyma of the lungs [1]. Besides these conditions, MDS is rarely complicated by interstitial lung diseases, such as interstitial pneumonia [2, 3], bronchiolitis obliterans with organizing pneumonia (BOOP) [1, 4], and lung involvement associated with Sweet’s disease [1, 5, 6]. Here, we describe a case of steroid-responsive interstitial pneumonia, which developed in parallel with the progression of MDS. A 76-year-old Japanese woman who had been diagnosed with refractory anemia (RA) with normal karyotype 6 years previously was admitted to our hospital because of a 2-week history of fever, productive coughs and respiratory distress. On admission, physical examination disclosed a temperature of 37.5 C and coarse crackles over the lower fields of both lungs. Hematologic examination demonstrated a WBC count of 5.1 9 10/L with 2% blasts; a hemoglobin concentration of 8.7 g/dL and a platelet count of 378 9 10/L. She also had high levels of serum lactate dehydrogenase (528 IU/L) and C-reactive protein levels (7.24 mg/dL). Arterial blood gas analysis on room air showed an oxygen partial pressure of 54.4 mmHg, carbon dioxide partial pressure of 41.5 mmHg and pH of 7.47. Serology for autoimmune diseases and fungal antigen tests were negative. Blood and sputum cultures were negative for pathogens. Bone marrow aspirate and biopsy demonstrated hypercellular marrow with 15% blasts, and trilineage dysplasia without myelofibrosis. Cytogenetic analysis demonstrated an abnormal complex karyotype: 47,XX, der (5;17) (p10; q10), ?8, del (13) (q12q14) in the bone marrow cells. Thus, disease progression of RA to refractory anemia with excess blasts (RAEB)-2 was confirmed. Chest roentgenogram showed patchy infiltrates in the lower lobes of both lungs. A computed tomography (CT) scan of the chest demonstrated multiple patchy consolidation and ground-grass opacities in both lungs (Fig. 1a). Despite empirical treatment with broad-spectrum antibacterial and antifungal agents, oxygenation progressively deteriorated and fever persisted over the following weeks. Subsequent CT scan of the chest showed that the infiltrates had expanded and migrated along the bronchovascular bundles, suggesting BOOP. She had high levels of serum sialylated carbohydrate antigen KL-6 (1160 U/mL; normal range 0.0–500.0 U/mL) and surfactant protein D (419.1 ng/mL; normal range 0.0–110.0 ng/mL). Thereafter, fiberoptic bronchoscopy was performed, which did not show any endobronchial abnormalities. Bronchoalveolar lavage (BAL) fluid analysis demonstrated increased total cell count (5.3 9 10/mL), which was predominantly composed of lymphocytes with an elevated CD4/8 ratio of 2.53. Neither pathogenic microorganisms nor malignant cells were observed in the BAL fluid. Fluorescence in situ hybridization analysis detected an increase of cells showing trisomy 8 (6%), which should represent the MDS clone, in BAL fluid. Although radiographic and BAL findings suggested BOOP, histological examination of the specimen obtained by transbronchial lung biopsy demonstrated alveolitis with lymphocyte infiltration, which is compatible K. Kataoka M. Ichikawa A. Hangaishi T. Takahashi Y. Imai M. Kurokawa (&) Department of Hematology and Oncology, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan e-mail: kurokawa-tky@umin.ac.jp