A 60-year-old man comes to the office due to cough and dyspnea on exertion. The patient has had a cough for over 2 years, but it has become worse recently and is accompanied by increasing shortness of breath. The cough is productive with a small volume of mucoid sputum. He has no hemoptysis, chest pain, or leg swelling. The patient has a 40-pack-year smoking history and drinks 1 or 2 glasses of wine daily. He has worked in a shipyard for 10 years. Other medical conditions include rheumatoid arthritis and hypertension. Temperature is 37.2 C (99 F), blood pressure is 140/80 mm Hg, pulse is 80/min, and respirations are 20/min. Chest x-ray reveals prominent bronchovascular markings and mild diaphragmatic flattening. Pulmonary function test results are as follows:
| FEV1 | 67% of predicted |
| FVC | 95% of predicted |
| FEV1/FVC ratio | 0.65 |
Diffusion capacity of the lung for carbon monoxide is 100% of predicted value. Which of the following is the most likely cause of this patient's symptoms?
Differential diagnosis based on DLCO | |||
Obstructive pattern | Restrictive pattern | Normal spirometry | |
Low |
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Normal |
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Increased |
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DLCO = diffusing capacity of the lung for carbon monoxide. | |||
Chronic obstructive pulmonary disease (COPD) encompasses a spectrum of pathology ranging from chronic bronchitis to emphysema, eventually leading to nonreversible airflow obstruction (eg, pulmonary function testing [PFT] with decreased FEV1/FVC ratio, decreased FEV1). The resultant air trapping can lead to lung hyperinflation, seen as diaphragmatic flattening on chest x-ray.
This patient has a classic presentation of COPD with a predominant chronic bronchitis phenotype. Chronic bronchitis occurs due to irritant-induced airway mucosal inflammation, respiratory epithelium metaplasia, and mucus hypersecretion. It is defined as productive cough for ≥3 months over 2 consecutive years (not due to other causes) with or without airflow limitation. By contrast, emphysema involves proteolytic destruction of the alveolar walls. Some distinguishing features include the following:
The diffusing capacity of the lung for carbon monoxide (DLCO), which measures gas transfer between the alveoli and pulmonary capillary blood, remains normal in chronic bronchitis (intact alveolar and capillary membrane) but is decreased in emphysema, where destruction of the alveolar wall reduces the available gas exchange surface area.
The chest x-ray findings in chronic bronchitis reflect airway inflammation, including prominent thickened bronchovascular markings. In contrast, chest x-ray findings in emphysema reflect obliteration of the alveolar septa and include decreased lung tissue density (hyperlucency) and bullae.
Management of these 2 subgroups is similar, although the distinction can be useful in treating advanced cases. For example, patients with frequent exacerbations of chronic bronchitis gain more benefit from mucus clearance therapy (eg, chest percussion) and anti-inflammatory agents (eg, inhaled corticosteroids).
(Choices A, E, and F) Asbestosis, pulmonary fibrosis, and silicosis are examples of interstitial lung diseases that demonstrate a restrictive pattern on PFT, characterized by reduced lung volumes, roughly proportional decreases in FEV1 and FVC, normal or supranormal FEV1/FVC ratio, and low DLCO.
(Choice B) Bronchiectasis is a disease of abnormal bronchial widening in the setting of recurrent infection and inflammation. Its presentation can be similar to that of chronic bronchitis. However, sputum production is more prominent and voluminous, the chest x-ray reveals dilated (rather than thickened) conducting airways, and episodes of bacterial superinfection are common.
(Choice D) Panacinar emphysema is typical for alpha-1-antitrypsin deficiency; centriacinar emphysema is more characteristic for smoking-induced COPD. Both forms of emphysema usually cause a low DLCO.
Educational objective:
Chronic obstructive pulmonary disease (COPD) encompasses a spectrum of chronic bronchitis and emphysema. The diffusing capacity of the lung for carbon monoxide is normal in chronic bronchitis-predominant COPD and decreased in emphysema-predominant COPD.