The breakdown or disruption of the normal functioning of skeletal muscle, so that muscle cells release their contents into the bloodstream, including creatinine kinase (CK), a protein that increases when muscle is damaged, myoglobin, an iron-containing protein that transports and stores oxygen in muscle cells, and electrolytes.

Symptoms are muscle pain, weakness, and reddish-brown urine, but only 10% of patients will have all three.

Any form of muscle damage can lead to rhabdomyolysis, most commonly direct injury, impairment of blood flow in muscle tissue, and some drugs and toxins. Rhabdomyolysis is a known side effect of statin treatment, but occurs less frequently than patients may believe. If patients on statins develop muscle pain, muscle tenderness and weakness, the statin should be stopped immediately and CK checked urgently.

Diagnosis is confirmed by laboratory testing – CK levels are typically five times higher than the upper limit of normal.

Severe disease may cause acute kidney injury.