A 50-year-old woman is evaluated in the office for intermitt

[madhurima]

A 50-year-old woman is evaluated in the office for intermittent cough and dyspnea on exertion of 3 months' duration. There is no significant sputum production, and she does not have wheezing, chest pain or tightness, or peripheral edema. She has a 30-pack-year history of cigarette smoking. She has no other medical problems and takes no medications.
On physical examination, she is resting comfortably. Blood pressure is 134/82 mm Hg, heart rate is 60/min, respiration rate is 12/min, and oxygen saturation is 96% with the patient breathing room air. Breath sounds are normal with no adventitious sounds. Chest radiograph is normal.
Laboratory Studies
Forced vital capacity (FVC) 78% of predicted
Forced expiratory volume in 1 sec (FEV1) 76% of predicted
FEV1/FVC ratio 65% (0.65)
Diffusing capacity for carbon monoxide (DLCO) (single breath; corrected to hemoglobin) Normal
Which of the following is the most likely diagnosis?

1 asthma
2 chronic bronchitis
3 emphysema
4 interstitial lung disease
5 pulmonary embolism

[madhurima]

Answer and Critique (Answer = A)
Key Points
• A FEV1/FVC ratio <70% is indicative of obstructive lung disease.
• A ?12% increase in either the FEV1 or FVC and an increase of 200 mL or more from baseline in either parameter following administration of an inhaled bronchodilator are compatible with asthma.
The patient's short duration of symptoms, lack of increased sputum production, obstructive pattern on pulmonary function testing, and normal diffusing capacity for carbon monoxide (DLCO) are most compatible with the diagnosis of asthma. Spirometry values >80% of predicted are categorized as normal. A FEV1/FVC ratio of <70% (0.70) is indicative of obstructive lung disease. Obstructive lung disease also causes a decrease in vital capacity and an increase in residual lung volumes because of air trapping. If initial spirometry results are abnormal and suggest obstructive disease, the test is repeated after administration of an inhaled bronchodilator. An increase ?12% in either the FEV1 or FVC and an increase of 200 mL or more from baseline in either parameter constitute a significant response and are compatible with reversible airways obstruction (i.e., asthma).
The DLCO reflects the integrity of the alveolar-capillary membrane. Patients with emphysema have a reduced DLCO because of loss of lung parenchyma and less surface area for diffusion and those with pulmonary embolism have a reduced DLCO because of decreased blood flow through the pulmonary vasculature. Interstitial lung disease typically causes a diffusion barrier and is also associated with abnormal findings on chest radiograph or high-resolution CT scan. In patients with bronchitis and asthma, the alveolar-capillary membrane is intact and therefore diffusion is normal; however, bronchitis is associated with cough and increased sputum production, which are absent in this patient.