Dr. Kim of the University of Alabama at Birmingham has no relevant financial relationships to disclose.)
This article includes discussion of myoglobinuria and rhabdomyolysis. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Rhabdomyolysis refers to the breakdown of striated muscle that is followed by leakage of the muscle protein myoglobin into the blood, leading to its excretion in the urine. This phenomenon is called myoglobinuria. The etiology of rhabdomyolysis is diverse and includes hereditary (metabolic diseases, dystrophinopathies, channelopathies) and acquired disorders (excessive muscular stress, ischemia, toxic damage, infections). Epidemiologic studies have shown that the etiology of a significant percentage of patients with recurrent myoglobinuria remains unknown. It is thought that these patients may have as yet undiscovered disorders of muscle metabolism. In this article, the authors review the epidemiology of myoglobinuria in the adult and pediatric populations, and the metabolic causes leading to recurrent myoglobinuria.
Historical note and terminology
Myoglobinuria can be defined as elevation of serum creatine kinase (CK) level of at least 10 times the upper limit of normal followed by its rapid decrease to (near) normal values. The clinical presentation is variable. The classical features are myalgia, weakness, and pigmenturia. However, this triad is seen in less than 10% of patients. Myoglobinuria indicates urinary excretion of the oxygen-binding muscle protein myoglobin. The presence of myoglobin in urine occurs when there is necrosis of muscle and leakage of muscle cell content in the blood. The urine appears pigmented with a brownish color when myoglobin concentration is over 100 µg/mL (Bagley et al 2007). Rhabdomyolysis indicates lysis of striated muscle and has been employed increasingly since the 1960s to denote the abrupt muscle injury that causes myoglobinuria. Myoglobinuria and rhabdomyolysis are used interchangeably.
Pigmenturia in association with symptoms of muscle injury was recognized in the German literature in the late 19th century as a disorder that affected horses and humans (Hed 1955). Over the first half of the 20th century, biochemical studies led to identification and characterization of the muscle heme protein, myoglobin, and elucidation of its role in transporting oxygen from hemoglobin to mitochondria (Kagen 1973). Parallel clinical observations established more firmly the link between muscle injury and the urinary excretion of myoglobin and began to outline the epidemiology of this syndrome. Of special note are the studies of Bywaters, which identified myoglobinuria as a complication of muscle crush injuries sustained in the Battle of Britain in World War II; described acute renal failure as a complication of myoglobinuria; and performed seminal experimental studies implicating myoglobin (rather than other constituents of injured muscle) in the pathogenesis of renal injury (Bywaters 1944).
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