Nontraumatic Exertional Rhabdomyolysis Leading to Acute Kidney Injury in a Sickle Trait Positive Individual on Renal Biopsy

A 26-year-old African American male with a history of congenital cerebral palsy, sickle cell trait, and intellectual disability presented with abdominal pain that started four hours prior to the hospital visit. The patient denied fever, chills, diarrhea, or any localized trauma. The patient was at a party at his community center last evening and danced for 2 hours, physically exerting himself more than usual. Labs revealed blood urea nitrogen (BUN) level of 41 mg/dL and creatinine (Cr) of 2.8 mg/dL which later increased to 4.2 mg/dL while still in the emergency room. Urinalysis revealed hematuria with RBC > 50 on high power field. Imaging of the abdomen revealed no acute findings for abdominal pain. With fractional excretion of sodium (FeNa) > 3%, findings suggested nonoliguric acute tubular necrosis. Over the next couple of days, symptoms of dyspepsia resolved; however, BUN/Cr continued to rise to a maximum of 122/14 mg/dL. With these findings, along with stable electrolytes, urine output matching the intake, and prior use of proton pump inhibitors, medical decision was altered for the possibility of acute interstitial nephritis. Steroids were subsequently started and biopsy was taken. Biopsy revealed heavy deposits of myoglobin. Creatinine phosphokinase (CPK) levels drawn ten days later after the admission were found to be elevated at 334 U/dl, presuming the levels would have been much higher during admission. This favored a diagnosis of acute kidney injury (AKI) secondary to exertional rhabdomyolysis. We here describe a case of nontraumatic exertional rhabdomyolysis in a sickle cell trait (SCT) individual that was missed due to findings of microscopic hematuria masking underlying myoglobinuria and fractional excretion of sodium > 3%. As opposed to other causes of ATN, rhabdomyolysis often causes FeNa < 1%. The elevated fractional excretion of sodium in this patient was possibly due to the underlying inability of SCT positive individuals to reabsorb sodium/water and concentrate their urine. Additionally, because of their inability to concentrate urine, SCT positive individuals are prone to intravascular depletion leading to renal failure as seen in this patient. Disease was managed with continuing hydration and tapering steroids. Kidney function improved and the patient was discharged with a creatinine of 3 mg/dL. A month later, renal indices were completely normal with persistence of microscopic hematuria from SCT.