A 62-year-old man comes to the office due to a year of progressive exertional dyspnea and dry cough. He lives by himself and has been having difficulty performing daily activities. The patient has a history of gastroesophageal reflux and osteoarthritis. He has smoked a pack of cigarettes daily for 40 years and occasionally drinks alcohol. The patient worked as a carpenter for 20 years, and before that, he repaired navy ships. He has no pets or recent travel history. Blood pressure is 140/80 mm Hg and pulse is 80/min and regular. Pulse oximetry is 92% on ambient air. BMI is 33.2 kg/m². Chest x-ray reveals pleural calcifications. Pulmonary function studies are as follows. Which of the following is the most likely cause of this patient's symptoms?

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11ec25c8_d4b6_cf63_bc81_6d5967a102b1_MD0003_00 This patient likely has interstitial lung disease (ILD) due to occupational dust exposure. ILD is a collective term referring to multiple etiologies of progressive fibrosis affecting the pulmonary interstitium, alveoli, and conducting airways. Etiologies of ILD include chronic inhalation of organic/inorganic dust (eg, asbestos, beryllium, silicon dioxide), drug toxicity (eg, amiodarone, bleomycin, nitrofurantoin), radiation, and systemic connective tissue disease (eg, rheumatoid arthritis, scleroderma). Clues to the diagnosis in this patient include the characteristic symptoms of progressive dyspnea and nonproductive cough, history of navy shipyard work (risk factor for asbestos exposure), and pleural plaques on chest x-ray (consistent with asbestos exposure). In addition, pulmonary function testing (PFT) reveals the characteristic restrictive pattern of decreased FEV₁ and FVC and a normal (or sometimes increased) FEV₁/FVC ratio. The diffusion capacity of the lung for carbon monoxide (DLCO), which measures gas transfer between alveoli and pulmonary capillary blood, is decreased in ILD (due to fibrosis). DLCO allows differentiation from extrinsic causes of restrictive pulmonary physiology (eg, obesity hypoventilation syndrome [OHS], myasthenia gravis, amyotrophic lateral sclerosis), in which diffusion across the alveolar-pulmonary capillary membrane remains normal. (Choice A) Pleural calcifications are commonly seen in patients with asbestos exposure, but it is pulmonary fibrosis, not pleural calcifications, that causes respiratory compromise in these patients. (Choice C) PFT in chronic pulmonary thromboembolism typically demonstrates a normal FEV₁, FVC, and FEV₁/FVC ratio. The DLCO is decreased due to ventilation/perfusion mismatch and impaired gas exchange. Pleural calcifications would not be expected. (Choice D) Severe obesity limits thoracic cavity expansion in patients with OHS, resulting in a restrictive pattern on PFT. However, the DLCO remains normal and cough is not typically present. (Choice E) Smoking-induced alveolar destruction and hyperinflation describes emphysema in chronic obstructive pulmonary disease. An obstructive pattern is demonstrated on PFT, with a decreased FEV₁, normal FVC, and decreased FEV₁/FVC ratio. The DLCO is also decreased due to alveolar destruction. Educational objective: Interstitial lung disease (ILD) is a disease of progressive pulmonary fibrosis characterized by restrictive physiology on pulmonary function testing (decreased FEV₁ and FVC with a normal or an increased FEV₁/FVC ratio). The diffusion capacity of the lung for carbon monoxide is decreased in ILD but remains normal in extrinsic causes of restrictive pulmonary physiology.

A 62-Year-Old Man Comes to the Office Due to a Year