A 24 y/o M presents after running a marathon with diffuse myalgias and dark urine. He states he has been trying keeping up with hydration to the best of his ability, but it is an unseasonably warm November day.
What is your leading diagnosis? What are your treatment options? What are common and dangerous complications?
This is a case of rhabdomyolysis, which is caused by acute necrosis of skeletal muscle fibers and leakage of cellular contents into the blood. In addition to exertional rhabdomyolysis, other causes include alcohol and drug abuse, medication side effects (antipsychotics, benzos, steroids, INH, lithium, salicylates, SSRi, statins, TCAs, among others), chronic muscle disorders, trauma, NMS, seizures, immobility, infection, and heat-related illness. The release of myoglobin, CK, aldolase, LDH, and K are what underlie the downstream negative effects of skeletal muscle breakdown. Symptoms can include myalgias weakness, low grade fever, and dark urine. In severe cases, you may see nausea, vomiting, abdominal pain, and tachycardia. Muscle involvement is varied and dependent on cause.
Diagnosis should include serum CK levels- it begins to rise 2-12 hours after onset of injury, and peaks in 24-72 hours. Myoglobin is found in skeletal and cardiac muscles, and its serum level elevation occurs even before CK elevation, but is more rapidly cleared through renal excretion. Since myoglobin contains heme, a urine dip won’t differentiate hemoglobin from RBCs from myoglobin – therefore suspect myoglobinuria when the dip is (+) for blood, but negative for RBCs on micro analysis.
The most dangerous complications of rhabdomyolysis is acute renal failure, DIC, metabolic abnormalities (hyperkalemia, hyperphosphatemia, hyperuricemia, hypocalcemia), compartment syndrome, and peripheral neuropathy. Up to 46% of patients with rhabdo have been shown to develop ARF. This is exacerbated by concurrent dehydration, heat stress, and trauma (common in marathon runners).
Treatment involves large volume saline hydration. According to some recommendations, the fluid deficit should be corrected with oral hydration and/or crystalloid infusion with goal of urine output 2mL/kg/h. There is not good evidence available for use of urine alkalinazation or diuretics. Important considerations of monitoring during treatment of sicker patients include monitoring for arrhythmias, and of electrolytes, as hyperkalemia, hypocalcemia, and hyperphosphatemia can be severe early on.
