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As you are cleaning off your desk one Saturday morning you find the following results from pulmonary function tests:
fvc 4.13 L (93% of predicted)
FEV1 3.29 (88%)
FEV1/FVC 0.80
VC 4.2L (95%)
TLC 5.54L (98%)
FRC 3.03L (97%)
DLCO 20.7 ml/mm Hg /min (61%)



Unfortunately, the patient™s name, age, and other identifying information are not on the report, and you need to be able to match it with the appropriate patient. You try to remember all the patients you saw in the previous week and their suspected diagnoses. Then you review the results of the pulmonary function tests. Which of the following diagnoses is most consistent with these pulmonary function tests?
A. Bronchiolitis obliterans
B. Chronic pulmonary thromboembolic disease
C. Interstitial pulmonary fibrosis
D. Lymphangioleiomyomatosis (LAM)
E. Sarcoidosis

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A?

why A?

It is indicative of an obstructive pattern of disease, hence out of the given options I'd choose A, rest are probably restrictive . Is it ok ?

The correct answer is B. The key to answering this question is to identify the abnormality in the pulmonary function testing. The spirometric values are normal (FVC and FEV1), indicating no obstructive ventilatory defect. Similarly, the lung volumes are normal, and therefore no restrictive ventilatory defect is present. The lone abnormality is a reduced diffusing capacity for carbon monoxide. A pearl for interpreting pulmonary function tests is that an abnormal DLCO in the setting of normal spirometry and lung volumes suggests the presence of pulmonary vascular disease. Only chronic pulmonary thromboembolic disease might present with this pattern.

In contrast with choice B, choices A, C, D, and E are parenchymal lung diseases, and they often manifest with abnormal spirometry and/or lung volumes. Bronchiolitis obliterans (choice A) and LAM (choice D) are characterized by obstructive ventilatory defects and should present with abnormal spirometry. Interstitial pulmonary fibrosis (choice C) and sarcoidosis (choice E) typically present with restrictive defects. It is true, however, that early interstitial lung disease may present with only a reduced diffusing capacity, although this is rarely seen.

Good one.