A 20-year-old man comes to the emergency department with painful
muscle spasms. He notices that these episodes worsen after a run and seem to improve after brief periods of rest. His past medical history includes a right knee
ACL tear. His temperature is 37.0°C (98.6°F),
pulse is 80/min, respirations are 16/min, and
blood pressure is 125/75 mmHg. Abdominal examination is unremarkable. Rapid fingerstick glucose is 80 mg/dL. Serum creatine kinase levels are elevated. Laboratory investigations are shown below:
| Serum |
| Sodium | 140 mEq/L |
| Potassium | 4 mEq/L |
| Creatinine | 1.3 mg/dL |
| Creatine kinase | 645 U/L |
| Urine |
| BUN/Cr | <15 |
| Blood | Positive |
| Erythrocytes | 0/hpf |
| Leukocytes | 2/hpf |
| Fractional excretion of sodium (FENa) | >2% |
Electrocardiogram and echocardiogram are unremarkable. Which of the following is the most likely diagnosis?
