A tile factory worker presenting with breathlessness and dry cough

Jenny, a nonsmoker, 54 years of age, presents with 3 years of dry cough, progressive breathlessness and reducing exercise tolerance. Two years ago she was diagnosed with asthma and treated with inhaled bronchodilators (which have been marginally effective). Jenny has worked in a tile factory for 22 years; 15 years in the grinding department, transferring to the chipping department 7 years ago. On examination she is tachypnoeic with a prolonged expiratory phase. There are bilateral rhonchi and a few fine crepitations at the left infrascapular region. Jenny's full blood count and electrocardiogram are normal. Arterial blood gas show mild hypoxia with respiratory alkalosis. Spirometry demonstrates mixed moderate obstructive and restrictive impairment. The diffusion capacity for carbon monoxide is reduced. Mantoux is negative and erythrocyte sedimentation rate is 10 mm/hour. A chest X-ray is taken.