Rhabdomyolysis-Associated Acute Kidney Injury With Normal Creatine Phosphokinase

Rhabdomyolysis is a syndrome characterized by the breakdown of skeletal muscle and leakage of intracellular myocyte contents, such as creatine phosphokinase (CPK) and myoglobin, into the interstitial space and plasma resulting in acute kidney injury (AKI). Elevated CPK of at least 5 times the upper limit of normal is an important diagnostic marker of Rhabdomyolysis. We present a case of rhabdomyolysis with severe AKI with a normal CPK at presentation. A 32-year-old man presented with acute respiratory failure and AKI after an overdose of recreational drugs. Urinalysis at presentation showed trace amounts of blood, identified as rare red blood cells under microscopy. CPK was 156 U/L at presentation. Workup for glomerulonephritis and vasculitis was negative. He was initiated on renal replacement therapy, and a kidney biopsy showed severe acute tubular injury with positive myoglobin casts. Supportive management and renal replacement therapy was provided, and renal function spontaneously improved after a few weeks. This is an uncommon clinical presentation of severe rhabdomyolysis complicated by AKI. This suggests that CPK alone may not be a sensitive marker for rhabdomyolysis-induced AKI in some cases.