The image shows a frozen cross section of skeletal muscle from a patient with rhabdomyolysis, which included the full clinical syndrome of muscle pain, weakness, dark urine, and markedly elevated serum creatine kinase. The image shows three necrotic fibers engulfed by macrophages (arrow). So what causes such muscle injury? The broad differential diagnosis includes trauma, drugs (e.g. statins, alcohol, heroin, cocaine), toxins (e.g. metabolic poisons, animal venom), inflammatory myopathy, immune-mediated necrotizing myopathy (e.g. anti-HMG CoA reductase associated myopathy), infection (e.g. EBV, influenza), paraneoplastic myopathy, and metabolic myopathy (e.g. disorders of glycolysis, lipid metabolism, mitochondria).