Viral Myositis and Dermatomyositis: Key Diagnostic Differences

Myalgias causing an inability to ambulate after a viral illness is a concerning presentation for children, their parents and healthcare providers. Benign acute childhood myositis (BACM) and post-viral myositis (PVM) are typically distinguishable from juvenile dermatomyositis (JDM), but in exceedingly rare cases, they may present similarly, complicating the diagnosis. We report a unique case of a 4-year-old boy with severe myalgias and inability to ambulate following a norovirus infection. He also exhibited periorbital edema resembling a heliotrope rash, accompanied by significantly elevated levels of creatine kinase (CK), alanine transaminase (ALT), and aspartate transaminase (AST), raising concern for juvenile dermatomyositis, especially as he had a poor response to conservative medical management and his symptoms had persisted for two months. This case underscores the diagnostic challenges in distinguishing BACM/PVM from JDM, particularly when an uncommon viral pathogen like norovirus presents with a heliotrope rash—an eruption often considered pathognomonic for dermatomyositis.