Chest radiography is the most appropriate diagnostic test to perform next in this patient with polymyositis who has positive anti–Jo-1 antibodies and features of the antisynthetase syndrome. Pulmonary manifestations of dermatomyositis and polymyositis are common and may result from interstitial lung disease (ILD), hypoventilation (weakness of respiratory muscles), aspiration pneumonia, and, rarely, pulmonary arterial hypertension (PAH). Clinical manifestations of ILD range from being asymptomatic to severe progressive cough and dyspnea. ILD is strongly associated with the presence of positive autoantibodies to transfer RNA synthetases, including anti–Jo-1 antibodies. In clinical practice, chest radiography, high-resolution chest CT, and pulmonary function testing are used to evaluate for the presence of this manifestation, and periodic follow-up in an asymptomatic patient is appropriate. Various patterns of ILD occur, ranging from nonspecific interstitial pneumonitis (most common) to usual interstitial pneumonia or bronchiolitis obliterans organizing pneumonia. The pattern of involvement determines glucocorticoid responsiveness and, ultimately, prognosis.

6-Minute walk testing is an important test used in the evaluation and follow-up of patients with an established diagnosis of PAH, but there is no evidence that this patient has PAH.

Myocarditis has a highly variable presentation, including fatigue, chest pain, heart failure, cardiogenic shock, arrhythmias, and sudden death. This patient has no cardiovascular symptoms suggesting myocarditis, and a cardiac MRI is not necessary in a patient with a low suspicion for this condition.

Coronary artery disease most classically presents with exertional substernal chest pain relieved with rest or nitroglycerin. Variant presentation may include dyspnea on exertion and exertional fatigue. Exercise stress testing would be indicated if there was a high level of suspicion for coronary artery disease, which is not the case here.

No additional testing is incorrect because ILD may be asymptomatic in some patients and can be missed without additional testing.