Acute Muscle Injury and Subcutaneous Edema in a Patient with Anti-nuclear Matrix Protein-2 Antibody Positive Dermatomyositis Sine Dermatitis.

This case describes anti-nuclear matrix protein-2 (NXP-2) antibody-positive dermatomyositis sine dermatitis (DMSD) with an acute onset and marked creatine kinase (CK) elevation, closely mimicking drug-induced rhabdomyolysis. The patient lacked a skin rash and initially improved with hydration, but later developed respiratory failure, leading to a diagnosis via a muscle biopsy and antibody testing. Notably, the imaging findings also resembled rhabdomyolysis, further complicating differentiation. This case highlights that when anti-NXP-2-positive myositis presents as DMSD with acute, transient CK elevation and rhabdomyolysis-like imaging, however, distinguishing between these two conditions is extremely difficult. In such atypical cases, a muscle biopsy plays a critical role and should be actively considered for the diagnosis.