Cryptogenic organising pneumonia Is characterised by all of the following except

In cryptogenic organizing pneumonia,pulmonary function is impaired with a restrictive defect and aerial hypoxaemia,being most common.Chest X ray shows bilateral,patchy/diffuse,recurrent & migratory pulmonary opacities.These changes are more frequent in the periphery of the lung and in the lower lung zone.Glucocoicoid therapy induces clinical recovery in two-thirds of patients. Reference:Harrison's medicine-18th edition,page no:2166,2167.