A 27-year-old man presents to the emergency department with altered mental status. He was running a marathon but became confused halfway through the race. He arrives unable to coherently answer questions and is not sure where he is. He has a history of a seizure disorder. His temperature is 105°F (40.6°C), blood pressure is 116/68 mmHg, pulse is 167/min, respirations are 29/min, and oxygen saturation is 99% on room air. Physical exam reveals a confused man who is moving all 4 extremities and is protecting his airway. During the exam, he develops a tonic-clonic seizure, which lasts 1 minute and then terminates on its own. The patient is given intravenous fluids, and basic laboratory studies are drawn and pending. A urine dipstick is positive for red blood cells. Which of the following is most likely to be seen on laboratory testing?
Hyponatremia
Hyperkalemia
Hyperuricemia
Hypocalcemia
Hypocalcemia
This patient is presenting after running a marathon with hyperthermia and altered mental status suggestive of heatstroke. In the setting of his recent exertion, tonic-clonic seizure, and urine dipstick positive for red blood cells, he is likely suffering from rhabdomyolysis, which most commonly causes hypocalcemia.

Rhabdomyolysis occurs when there is a breakdown of the muscle cells. It can occur with exertion (such as marathon running or weight lifting), seizures (from prolonged and intense contraction of the muscles), cocaine use, lightning strikes, electrical injuries, and crush injuries. Damage to muscle cells most commonly causes hypocalcemia from the deposition of calcium in necrotic muscle cells as well as calcium sequestration by the muscle sarcoplasmic reticulum. Symptoms of hypocalcemia include perioral numbness and tetany, altered mental status, and seizure. ECG manifestations of hypocalcemia include QT prolongation. There is no treatment needed for hypocalcemia in rhabdomyolysis unless it is severe or is causing symptoms such as seizure or ECG changes. The management of rhabdomyolysis involves aggressive IV fluid administration titrated to urine output in order to prevent myoglobin nephrotoxicity. Myoglobin causes the classic false-positive finding of red blood cells on urine dipstick given the cross-reactivity of myoglobin and hemoglobin on this test.

Giannoglou et al. review the pathophysiology and diagnosis of rhabdomyolysis. The authors find that hypocalcemia is the most common electrolyte derangement seen in rhabdomyolysis. The authors recommend carefully monitoring ionized calcium in patients with rhabdomyolysis.

Incorrect Answers:
Answer A: Hyperkalemia is a common electrolyte derangement that occurs in rhabdomyolysis and can cause life-threatening dysrhythmias. Initial ECG findings suggestive of hyperkalemia include peaked T waves and QRS widening. The management of hyperkalemia involves the administration of calcium chloride to stabilize cardiac membranes followed by insulin, albuterol, and bicarbonate. Severe/refractory hyperkalemia can be treated with dialysis, but this is usually not needed in rhabdomyolysis. Hyperkalemia is less common when compared to hypocalcemia in rhabdomyolysis and does not cause seizures.

Answer B: Hyperphosphatemia is common in rhabdomyolysis and occurs secondary to the release of phosphorus from damaged muscle cells. Hyperphosphatemia does not usually require treatment in rhabdomyolysis, though phosphate restriction and phosphate binders can be administered. Hyperphosphatemia can rarely lead to seizures, though this is uncommon.

Answer C: Hyperuricemia is possible in rhabdomyolysis, occurs secondary to the release of purines from injured muscle cells, and is worsened by acute kidney injury which is common in rhabdomyolysis. The treatment of hyperuricemia in rhabdomyolysis involves IV fluids, rasburicase, and allopurinol (which works slowly).

Answer E: Hyponatremia may occur after running a marathon where the individual sweats out sodium, chloride, and water but rehydrates with only water. While this is possible in this patient and his seizure could reflect a hyponatremic seizure (which usually would not spontaneously resolve and requires hypertonic saline), there is concrete evidence of rhabdomyolysis with the positive urine dipstick for red blood cells.

Bullet Summary:
Rhabdomyolysis can cause hyperkalemia, hyperphosphatemia, and hypocalcemia (the most common electrolyte disturbance).