A 39-year-old woman presented to the emergency department (ED) with a chief complaint of muscle aches and pain. She stated that three days earlier, she had begun exercising in a 45-minute “spinning” class (ie, riding a stationary bicycle with a weighted front wheel). The patient had not engaged in any aerobic exercise for at least six months before the spinning class. She mentioned that much older participants in the class were outperforming her, but she did not feel the need to keep up with them.
After dismounting, the woman said, she experienced weakness in her legs and had great difficulty ambulating. She went home, took 400 mg of ibuprofen, and went to bed. She awoke with pain and swelling in both thighs and continued to take ibuprofen, in addition to applying a topical mentholated preparation to her thighs. She took an Epsom salts bath two days later.
On the morning of the third day after the spinning class, she voided black urine and presented to the ED.
The patient had no significant medical history. Surgical history was limited to removal of a ganglion cyst on her wrist. She denied any history of seizure disorder, thyroid disease, hepatitis, heart disease, or hyperlipidemia.
The patient had been taking ibuprofen as needed since the spinning class. She was taking no other medications. She denied any allergies to drugs or food.
The patient admitted to smoking one pack of cigarettes per week and to occasional alcohol consumption but denied use of illicit drugs. She was employed as an executive officer for a large business association.
On physical examination, the patient’s vital signs were blood pressure, 134/73 mm/Hg; pulse, 86 beats/min; and respirations, 16 breaths/min. She was afebrile, alert, and oriented. Her sclera were nonicteric. Her neck was supple with no anterior cervical lymphadenopathy. There was no thyroid enlargement, her lungs were clear to auscultation, and her heart sounds were regular. There was no peripheral edema, and dorsalis pedis pulses were present bilaterally. Her thighs appeared swollen but were not tender to palpation.
The patient’s history, combined with an extremely high level of serum creatine phosphokinase (CPK; ie, 123,800 U/L [reference range, 45 to 260 U/L1]), confirmed a diagnosis of rhabdomyolysis. She was admitted for close observation. The patient’s urinalysis revealed 2 to 5 red blood cells and 6 to 10 white blood cells per high-power field. Moderate occult blood was detected, with no casts or protein noted. A urine myoglobin test was not performed.
The patient underwent IV hydration with dextrose 5% in water and three ampules of sodium bicarbonate after being given a 2.0-L saline bolus. Ibuprofen was discontinued. IV hydration with bicarbonate solution was continued until the patient’s CPK level declined significantly. She underwent daily laboratory testing (see Table 1). Her renal function remained stable, and she was discharged on hospital day 7.
DISCUSSION
Rhabdomyolysis is a clinical condition defined as muscle necrosis resulting from the release of intracellular skeletal muscle components (including myoglobin, CPK, potassium, phosphorus, and aldolase) into the extracellular compartment.1-3 The condition was first described during the bombing of London in World War II, with high incidence of crush injuries, shock, and associated kidney damage.4 The preponderance of such injuries during a 1988 earthquake in Armenia led the International Society of Nephrology to form its Renal Disaster Relief Task Force, which has provided support at numerous other disaster scenes since then.5
Rhabdomyolysis has been identified with a variety of pathologic events: those that cause muscle trauma, those associated with muscle use or overuse, and other etiologies involving genetic, metabolic, infectious, or pharmaceutical factors.1 Many of the reported causes of rhabdomyolysis are listed in Table 2.1,2
For patients with muscle trauma, the etiology of rhabdomyolysis is clear, but for those with other disease states, diagnosis may be more elusive. Patients who present with rhabdomyolysis after excessive exercise, for example, may have underlying metabolic disorders that predispose them to exertional rhabdomyolysis, such as chronic hypokalemia resulting from primary hyperaldosteronism.1 Others may have a muscle enzyme deficiency, as in McArdle’s syndrome or carnitine deficiency.6
Alterations in blood chemistries can also contribute to development of rhabdomyolysis, even when more obvious etiologies for muscle necrosis are evident. Hypokalemia interferes with the vasodilation that normally occurs during exercise to increase muscle blood flow.1,7,8 Continued exercise can lead to muscle necrosis, raising a concern for athletes who take diuretics.1 Hypophosphatemia leads to a state of muscle necrosis; this is of particular concern for alcoholic patients who receive hyperalimentation without repletion of phosphates.9
Diagnosis
Patients with rhabdomyolysis usually present with myalgias, darkened urine (red, brown, or black), and a clinical scenario that corroborates the diagnosis (ie, history of trauma, excessive exercise, use of an offending medication).1 Some patients may have minimal to absent symptoms or symptoms that occur only after exercise.3