High-resolution CT (HRCT) is the gold standard for evaluating parenchymal opacities seen on a plain radiograph. In addition, approximately 20% of patients with diffuse parenchymal lung disease have subtle interstitial abnormalities not detectable on a chest radiograph. For this reason, HRCT should even be considered in symptomatic patients with restrictive physiology on spirometry and a normal chest radiograph, such as this patient. The patterns seen on CT correlate with pathologic findings on an open lung biopsy and are a key diagnostic tool for evaluation of diffuse parenchymal lung disease, as may be present in this patient.
Bronchoscopic lung biopsy can provide enough tissue to demonstrate specific histopathologic features diagnostic of several specific disease processes, including carcinoma, sarcoidosis, and eosinophilic pneumonia. Bronchoalveolar lavage can provide additional diagnostic information, including culture, cytology, and cell differential. However, a lung biopsy and bronchoalveolar lavage would not be indicated until imaging studies confirmed the presence of diffuse parenchymal lung disease.
Cardiopulmonary exercise testing includes assessment of respiratory gas exchange during treadmill or bicycle exercise for a more detailed assessment of functional capacity and differentiation between potential causes of exercise limitation (cardiac, pulmonary, or deconditioning, versus volitional). It would not be the most appropriate next choice in a patient with increasing exercise limitation, pulmonary crackles, and restrictive findings on pulmonary function testing.
A ventilation-perfusion (V/Q) lung scan is the recommended initial test for evaluating chronic thromboembolic pulmonary hypertension (CTEPH). Patients with CTEPH have nonspecific symptoms and the diagnosis is often missed. However, patients with CTEPH typically have a mild restrictive or obstructive defect, although spirometry is often normal. Most patients will have a reduction in the DLCO out of proportion to any abnormalities in spirometry. A V/Q lung scan may be a consideration if this patient's HRCT scan is normal.