The classic triad of presenting symptoms consists of weakness, proximal muscle pain, and dark urine; however, symptoms frequently occur in isolation and the classic cola-colored urine is not always present. It is important to recognize that symptoms may be absent early on, particularly in the context of patients with intoxication or those "found down" (discovered unconscious), so a high degree of suspicion is warranted.
Rhabdomyolysis can occur in any age group or demographic. The causes of rhabdomyolysis include toxins / drugs (eg, prescription medications, over-the-counter medications, recreational drugs, accidental ingestions, insect stings), physical trauma (eg, crush injuries), exertion (eg, vigorous exercise, agitated delirium, seizures, electrocution), muscle ischemia / hypoxia (eg, prolonged immobilization / limb compression, thrombosis, dehydration), endocrine / metabolic disorders (eg, hypothyroidism, diabetic ketoacidosis), electrolyte derangements (eg, hypokalemia, hypophosphatemia), infections (eg, influenza, HIV), body temperature extremes (eg, malignant hyperthermia, neuroleptic malignant syndrome, hypothermia), and genetic disorders (eg, inborn errors of metabolism, muscular dystrophies). A triggering event is not always identifiable.
During muscle necrosis, intracellular myocyte contents, including potassium, phosphorous, creatinine kinase (CK), lactate dehydrogenase, uric acid, and myoglobin, spill into the bloodstream. Myoglobin, a heme-containing protein, is filtered by the kidneys and can become nephrotoxic at high concentrations via intrarenal vasoconstriction, tubular obstruction, and oxidative radical injury.
Diagnosis is made by serum CK levels greater than 5 times the upper limit of normal (ULN). A threshold of 10 times the ULN is often used when the patient is known to be taking a statin. CK levels will rise and fall rapidly over the course of hours to days. A history of immobilization, traumatic injury, or new medication or recreational drug use may precede the diagnosis. Muscle tenderness, weakness, and renal failure are not required for diagnosis.
M62.82 – Rhabdomyolysis
89010004 – Rhabdomyolysis
- Hematuria / hemoglobinuria – Look for red blood cells on urine microscopy. Urine dipstick alone is inadequate as false positives will occur.
- Hyperbilirubinemia / bilirubinuria
- Other pigmenturias (eg, dietary consumption of beets, medications such as rifampin)
- Inflammatory myopathy
- Polymyalgia rheumatica
- Chronic serum CK elevation (eg, from inborn errors of metabolism or mitochondrial myopathy) – In rhabdomyolysis, there will be an acute rise and fall in serum CK levels.
- Steroid myopathy
- Normal postexertion myalgias
- Myalgias from viral infection without presence of significant muscle breakdown
- Tumor lysis syndrome