A 42-year-old woman presents with gradually worsening dyspnea over the preceding 6 months. She has a mild nonproductive cough. She previously had been diagnosed with systemic sclerosis (scleroderma) but her skin thickening has been stable. She controls her Raynaud syndrome with amlodipine and her esophageal reflux with daily omeprazole. She has no renal disease or hypertension. On physical examination, her RR is 22/minute and resting O2 saturation is 92%. She has thickened, hide-bound skin on the face, torso, and abdomen. Lung examination shows mild “Velcro” rales in the bases bilaterally. Neck veins are flat. Cardiac examination is normal with normal P 2 and no lift or heave. Chest x-ray shows increased interstitial lung markings and a normal heart size. What is the most important next step in evaluating this patient’s dyspnea?
A. Arterial blood gasThis patient has interstitial lung disease (ILD) due to her systemic sclerosis. Over 75% of patients will have CT evidence of ILD. Now that scleroderma renal crisis can be managed with ACE inhibitors, ILD is the most common disease related cause of death in scleroderma. The two most important studies for the diagnosis of ILD are spirometry with measurement of diffusion capacity of carbon monoxide (DLCO) and high-resolution CT scan. The latter will show reticular interstitial thickening and subpleural microblebs. Advanced cases will show thickened fibrotic bands with parenchymal destruction known as honeycombing. Treatment of connective tissue disease associated ILD is unsatisfactory, but cyclophosphamide will slow progression in some patients. In addition to systemic sclerosis, ILD is an important potential complication of polymyositis/dermatomyositis, rheumatoid arthritis, and occasionally systemic lupus. An arterial blood gas study would probably show alveolar hyperventilation (ie, low PCO2 ) with a widened alveolar-arterial oxygen gradient but would not give specific information as to cause and prognosis. In most cases, finger oxygen saturation measurements provide sufficient information. Pulmonary hypertension can be detected with 2D echocardiogram according to the degree of tricuspid regurgitation. Pulmonary hypertension can be an important complication of connective tissue disease (especially limited scleroderma but sometimes diffuse scleroderma as well). You would expect, however, a loud P 2 and evidence of central pulmonary artery enlargement on CXR. In addition, Velcro rales and increased interstitial markings are not seen in uncomplicated pulmonary hypertension. Autoantibodies are usually found in systemic sclerosis, but the diagnosis is already established. The titer of anti-Scl antibodies does not correlate with disease activity; so once the diagnosis is established, serial measurement of autoantibodies is not necessary. Aspiration due to esophageal dysmotility can complicate scleroderma, but usually causes intermittent exacerbations associated with sputum production, fever, and alveolar infiltrates, none of which has characterized this patient’s course.