Biphasic Biochemical Pattern Suggestive of Second-Wave Muscle Injury in Exertional Rhabdomyolysis

BackgroundExertional rhabdomyolysis is an important cause of acute kidney injury (AKI) in otherwise healthy individuals following strenuous physical activity. Serum creatine kinase (CK) typically peaks within 24 to 72 h and progressively declines with appropriate supportive management. A secondary biochemical rise after initial improvement is uncommon and may reflect ongoing skeletal muscle injury.Case PresentationA 21-year-old previously healthy man presented with severe generalized myalgia, dark-colored urine, and progressive oliguria progressing to anuria following a prolonged trekking expedition. Initial investigations revealed severe rhabdomyolysis with a CK of 18,500 U/L, dialysis-requiring AKI (serum creatinine 9.0 mg/dL), hyperkalemia, hyperphosphatemia, hypocalcemia, metabolic acidosis, and myoglobinuria. Intermittent hemodialysis was initiated because of severe AKI with persistent anuria and metabolic complications. Serial biochemical monitoring initially demonstrated improvement; however, on the fourth hospital day, an unexpected secondary rise in CK (14,900-22,600 U/L) occurred, accompanied by recurrent hyperkalemia, hyperphosphatemia, worsening metabolic acidosis, and increased AST and LDH, despite ongoing renal replacement therapy. This biphasic biochemical pattern was considered suggestive of delayed or "second-wave" skeletal muscle injury. The patient received a total of 5 hemodialysis sessions with continued supportive care, following which urine output progressively improved, biochemical abnormalities resolved, and renal function recovered completely.ConclusionThis case highlights a rare biphasic biochemical pattern in severe exertional rhabdomyolysis, characterized by a secondary surge in muscle injury markers and metabolic abnormalities after initial improvement. Recognition of this potential "second-wave" phenomenon emphasizes the importance of continued serial CK and biochemical monitoring in patients with severe rhabdomyolysis.