A case of sarcoidosis with interstitial lung disease mimicking clinically amyopathic dermatomyositis and rapidly progressive interstitial lung disease.

Here, we report a patient with sarcoidosis who developed edematous erythema and interstitial lung disease. At the initial visit, clinically amyopathic dermatomyositis (CADM) with rapidly progressive interstitial lung disease (RP-ILD) was suspected because he had progressive dyspnea but no muscle weakness. The presence of anti-CADM-140/MDA5 autoantibodies was immediately assessed to facilitate a precise diagnosis, with negative results. Thereafter, skin and transbronchial lung biopsies revealed noncaseating granuloma with Langhans giant cells in both specimens, leading to a diagnosis of sarcoidosis. In this case, clinical features of skin and lung were unable to distinguish DM (including CADM) from sarcoidosis, but the lack of anti-CADM-140/MDA5 antibody was useful for differentiating CADM with RP-ILD mimicking sarcoidosis from bona fide sarcoidosis.