Exertional Heat Rhabdomyolysis in Class III Obesity Mimicking Nephrolithiasis and Hepatobiliary Disease.

Exertional rhabdomyolysis has been described in military recruits and endurance athletes, whereas recognition in adults with severe obesity performing routine activities remains limited. Diagnostic delays may occur when initial clinical features resemble those of more common conditions and creatine kinase is omitted from early evaluation. A 30-year-old man with class III obesity (body mass index 51 kg/m²) developed severe right flank pain over three days after lawn mowing in hot weather. On presentation, he was febrile to 39.1°C, tachycardic, met systemic inflammatory response syndrome criteria, and had right costovertebral angle tenderness. Initial laboratory assessment demonstrated a 3+ heme urine dipstick, fewer than three red blood cells per high-power field, elevated aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and normal alkaline phosphatase and bilirubin. Urologic and hepatobiliary evaluations were pursued, including computed tomography of the abdomen and pelvis and magnetic resonance cholangiopancreatography, whereas creatine kinase was not initially obtained. On admission the following morning, the presence of a dipstick-microscopy mismatch, AST-predominant transaminitis, recent heat exertion, and right thigh tenderness prompted the addition of creatine kinase to the diagnostic workup. Empirical isotonic crystalloid resuscitation was initiated before results were available. Creatine kinase was subsequently found to be 19,431 IU/L, and AST had declined from the emergency department value by the time of the result. Serum creatinine remained stable at 1.0 to 1.1 mg/dL, and the patient recovered without acute kidney injury. This case illustrates an atypical presentation of exertional rhabdomyolysis in which flank pain and transaminitis mimicked renal and hepatobiliary disease; recognizing the dipstick-microscopy mismatch and AST-predominant pattern after heat exertion should prompt clinicians to send creatine kinase and start fluids early.