Lung function testing in COPD: when everything is not so simple

Combined pulmonary fibrosis and emphysema is a condition occurring mainly in male smokers, presenting different lung mechanics and gas exchange abnormalities than emphysema or pulmonary fibrosis alone. We report the case of an elderly man, former heavy smoker, who presented with progressive exertional dyspnea for 1 year. Lung function tests showed near normal spirometry and lung volumes but marked reduction of diffusing capacity for carbon monoxide and even more nitric oxide. The arterial partial pressure of oxygen was reduced with a markedly increased alveolar-to-arterial difference. High-resolution computed tomography of the chest showed a pattern consistent with upper lobe emphysema and lower lobe pulmonary fibrosis. In conclusion, this case report confirms the limitations of a simplistic approach to lung function in the diagnosis of symptomatic smokers.