[A case of acute respiratory failure in an elderly patient with elderly asthma-COPD overlap syndrome (ACOS) is differentiated from acute eosinophilic pneumonia].

We report a case of acute respiratory failure in a 77-year-old male with chronic obstructive pulmonary disease (COPD) who showed marked eosinophilia (61.5% of the peripheral total white blood cells [WBCs]; 13,200/mm(3)). The patient was an ex-smoker, but he had started smoking again one month previously, His forced expiratory volume in one second (FEV1) was low and dyspnea symptom was observed. Although rhonchi were detected, wheezing chest sounds were not detected. Chest X-radiography and computed tomography of the lung revealed diffuse bilateral pulmonary infiltrates and emphysematous changes. He was given intravenous methyl prednisolone (1,000 mg) for 3 consecutive days. The abnormal shadows on the chest X-ray film improved remarkably and the eosinophils in his peripheral blood were reduced. Furthermore, it was no longer necessary to administer oxygen to treat his hypoxemia. The symptomatic and clinical course mimicked to a case of acute eosinophilic pneumonia (AEP). However, transbronchial lung biopsy specimens did not reveal eosinophilic infiltration in the alveolar septa. The fraction of eosinophils in the patient's bronchoalveolar lavage was 4.4% and not greater than 25%. After hospitalization, 5-15 mg of prednisolone administered orally in combination with bronchodilators to better manage his clinical symptoms. This case was thus determined to correspond to elderly asthma-COPD overlap syndrome (ACOS).