A 68-year-old man comes to the office due to progressive dyspnea on exertion and nonproductive cough over the past year. The patient now has dyspnea after performing common household chores. He had asthma during childhood but otherwise had no respiratory symptoms until a year ago. He has hypertension and osteoarthritis. Medications include lisinopril and acetaminophen as needed. The patient has never smoked and drinks alcohol on social occasions. He travelled overseas extensively during his long career in the navy but has been retired for 8 years. He has 2 dogs. Temperature is 37 C (98.6 F), blood pressure is 143/76 mm Hg, pulse is 93/min, and respirations are 20/min. Oxygen saturation is 94% on ambient air. BMI is 27 kg/m2. Neck veins are flat. Lung auscultation reveals fine inspiratory crackles at the bases, and heart sounds are normal without murmur. The abdomen is nontender without hepatosplenomegaly. No extremity edema is present. Which of the following sets of findings are most likely to be observed on pulmonary function testing of this patient?
Pulmonary function tests in chronic lung disease | |||||
Asthma | COPD | Interstitial lung diseases | Pulmonary arterial hypertension | Restrictive chest wall disease | |
TLC | Normal/↑ | ↑ | ↓ | Normal | ↓ |
FEV1/FVC | ↓* | ↓ | Normal | Normal | Normal |
DLCO | Normal/↑ | ↓† | ↓ | ↓ | Normal |
COPD = chronic obstructive pulmonary disease; DLCO = diffusing capacity for carbon monoxide; TLC = total lung capacity. *With positive bronchodilator response. †Normal in early COPD. | |||||
This patient with slowly progressive dyspnea, dry cough, and fine crackles in the absence of a smoking history likely has interstitial lung disease due to idiopathic pulmonary fibrosis (IPF). On pulmonary function testing, IPF is associated with:
Restrictive profile: Typically decreased total lung capacity (TLC) and normal FEV1/FVC ratio
Reduced diffusion capacity for carbon monoxide (DLCO): Likely due to decreased pulmonary capillary erythrocyte volume and alveolar-capillary surface area
IPF commonly presents at age 50-70; most patients have a history of smoking. In addition to fine bibasilar crackles, patients in advanced disease may develop end-inspiratory squeaks, digital clubbing, and an abnormal S2 (eg, loud P2; fixed, split S2) due to pulmonary hypertension.
Evaluation should include a thorough history to identify evidence of autoimmune disease, use of associated medications (eg, amiodarone), occupational exposures, and therapeutic radiation. For example, this patient's long career in the navy places him at increased risk due to asbestos exposure. Chest x-ray typically demonstrates nonspecific reticular infiltrates, but chest CT findings such as peripheral or basilar reticular infiltrates and honeycombing are more helpful in establishing the diagnosis. If imaging is nondiagnostic or the clinical picture is atypical, a biopsy can confirm the diagnosis.
(Choice B) An increase in TLC with drops in both FEV1/FVC and DLCO is associated with emphysematous chronic obstructive pulmonary disease. However, in the absence of a history of smoking, wheezing, or productive cough, this condition is less likely.
(Choice C) A reduction in the TLC without any changes to the FEV1/FVC ratio or DLCO is consistent with chest wall deformities due to diseases such as scoliosis or obesity.
(Choice D) Pulmonary arterial hypertension is associated with reductions in the DLCO without affecting either the TLC or the FEV1/FVC ratio. This patient does not have clear risk factors for isolated pulmonary arterial hypertension (eg, connective tissue disorders, liver disease) or examination findings that point to it (eg, abnormal S2, jugular venous distension).
(Choice E) Pulmonary function testing in asthma is variable but can demonstrate either normal or increased TLC and DLCO with reductions in the FEV1/FVC ratio. Although asthma can be characterized by dyspnea and cough, these symptoms occur episodically as patients are exposed to inflammatory triggers. This patient's slow, progressive worsening is more typical of IPF.
Educational objective:
Idiopathic pulmonary fibrosis is characterized by slowly progressive dyspnea, dry cough, and fine crackles and commonly occurs in patients age 50-70. It is associated with a restrictive profile and reduced diffusion capacity on pulmonary function testing.