Acute interstitial pneumonia due to amyopathic dermatomyositis.

Clinically amyopathic dermatomyositis usually presents with severe skin rashes but no muscle involvement and is associated with the highly lethal form of rapidly progressive interstitial lung disease. Diagnosis of myositis-related acute interstitial pneumonia can be particularly challenging, as the clinical presentation of hypoxia and respiratory failure has a broad differential diagnosis. This is especially true when the characteristic skin or muscle finding are absent and the patient has no history of idiopathic inflammatory myopathies. We present a rare case of a patient who presented with rapidly worsening acute respiratory failure from acute interstitial pneumonia due to an undiagnosed amyopathic dermatomyositis with positive anti-MDA5 autoantibody without any of the typical myositis symptoms or physical exam findings.