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  • Muscular pain, tenderness, or weakness.
  • Elevated creatine kinase MM.

Rhabdomyolysis is a disorder resulting from an injury or a metabolic defect in the skeletal muscle cell (myocyte) resulting in lysis of the cell membrane (sarcolemma) and leakage of its contents (myoglobin, enzymes, phosphorus, potassium) into the blood. Myoglobin is readily filtered by the glomerulus and when it appears in the urine it defines the term myoglobinuria. Although some patients experience few symptoms, most demonstrate muscular pain, tenderness, stiffness, and weakness. Serum creatine kinase (CK) of the MM isoform is nearly always elevated. A rare exception is diabetic myonecrosis, in which painful infarction of skeletal muscle, usually in the thigh, often occurs in the absence of a significant elevation in CK.

Table 11–1 shows a general classification for the causes of rhabdomyolysis.

Table 11–1. Causes of Rhabdomyolysis.

Normal subjects can develop modest rhabdomyolysis after intense exertion. Violent, repetitive activities or a grand mal seizure are good examples. Presumably, exhaustive exercise not only may directly injure structural components of muscle cells, but may also deplete energy stores, which lowers the normal threshold for injury. Other factors that lower the threshold for injury include poor physical condition or preexistent injury, typified by alcoholic myopathy. For any given unit of work, women unexplainably show much less rhabdomyolysis than men. Volume depletion and exercise in the heat, perhaps by causing overheating of muscle and reduced blood flow, are potentiating factors. Eccentric muscle contractions (running downhill) are more likely to cause rhabdomyolysis than concentric contractions (running uphill). Fasting lowers the threshold presumably by limiting substrates for muscle contraction. Severe trauma and crush injury commonly cause rhabdomyolysis and the related acute renal failure often contributes to the mortality of these conditions. Direct muscle injury during surgery may cause modest elevations of muscle enzymes.

Inherited Metabolic Myopathies

A number of specific enzyme derangements are responsible for exertional rhabdomyolysis by impairing energy metabolism. Classic examples are myophosphorylase deficiency (McArdle's syndrome) and carnitine palmityltransferase deficiency.

Acquired Metabolic Myopathies

Potassium deficiency is a typical example. Potassium deficiency impairs glycogen synthesis in muscle. Since glycogen is ...

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