To the Editors: Herein we report the progression of irreversible airflow obstruction in a patient with diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH). Following an episode of chronic eosinophilic pneumonia associated with raised sputum substance P and infiltration of the interstitum and alveolar spaces with eosinophils, the fixed airflow limitation became variable ( i.e. asthma), requiring treatment with inhaled corticosteroids and long-acting β-agonists. A number of airway diseases, such as smoker's bronchitis, emphysema, asthma, bronchiolitis and bronchiectasis, can lead to chronic airflow limitation 1. However, variability and reversibility of airflow limitation is only observed in asthma. Inflammatory cell infiltration of the airway, particularly with eosinophils, may be one of the mechanisms of variable airflow limitation 2. Although the natural history of eosinophilic bronchitis is not well known, it is believed that it may lead to chronic irreversible airflow limitation 3. However, it is unusual for chronic irreversible airflow limitation to show variability and improvement in airway calibre following treatment with corticosteroids. This case report describes the changes in lung function and response to treatment of a patient with chronic airflow limitation due to smoker's bronchitis and DIPNECH following eosinophilic inflammation of the airway and the interstitium. The case also highlights the importance of measuring airway inflammation in the management of airway diseases. A 65-yr-old female with a history of hypercholesterolemia, vertebral osteoarthritis, gall stone disease and endometriosis but no previous respiratory illness, except a mild intermittent cough for the past 4 yrs, presented with fever, night sweats, worsening cough and weight loss of 6.8 kg (15 lbs). She did not have muscle or joint aches, a skin rash or bowel symptoms. She appeared pale and had inspiratory crackles in her left axillary region. After accumulating a 12 pack-yr smoking history, she had quit smoking 15 yrs earlier. She had immigrated to Canada from …