Adil Abbasi MD, FACP

Learning Objectives

• Understand the pathophysiology linking rhabdomyolysis and acute kidney injury (AKI).
• Recognize the clinical features and diagnostic criteria for AKI in rhabdomyolysis.
• Review the laboratory evaluation and differential diagnosis.
• Outline the principles of management and prevention of AKI in patients with rhabdomyolysis.
• Summarize prognosis and long-term outcomes.

Introduction: Rhabdomyolysis and Its Renal Complications

Rhabdomyolysis is a clinical syndrome resulting from the breakdown of skeletal muscle fibers and release of their intracellular contents—including myoglobin, creatine kinase (CK), electrolytes, and other sarcoplasmic proteins—into the systemic circulation.
Acute kidney injury (AKI) is the most serious complication of rhabdomyolysis, occurring in up to 15–50% of cases depending on severity and setting【1】【2】.

Key Causes of Rhabdomyolysis

• Trauma (crush injuries, prolonged immobilization)
• Extreme exertion
• Drugs/toxins (statins, cocaine, alcohol)
• Infections
• Metabolic or genetic muscle disorders

Pathophysiology of AKI in Rhabdomyolysis

AKI in rhabdomyolysis is multifactorial, involving:

• Myoglobin-induced tubular toxicity
• Renal vasoconstriction and hypovolemia
• Tubular obstruction by myoglobin casts and uric acid

Mechanisms of AKI in Acute Rhabdomyolysis

1. Myoglobin Toxicity

• Myoglobin, released in massive amounts, is filtered by the glomerulus and accumulates in the renal tubules.
• In the setting of aciduria or hypovolemia, myoglobin is toxic to tubular epithelial cells and forms obstructive casts with Tamm-Horsfall protein.
• Free iron from myoglobin catalyzes formation of reactive oxygen species, causing oxidative injury【3】.

2. Hypovolemia and Vasoconstriction

• Muscle breakdown leads to sequestration of fluid in damaged muscle (third-spacing), causing hypovolemia and decreased renal perfusion.
• Renal vasoconstriction is also triggered by various vasoactive mediators and reduced nitric oxide.

3. Tubular Obstruction

• Myoglobin and uric acid precipitate in distal tubules, causing physical obstruction, especially in acid urine.

Clinical Features

Classic Triad

• Muscle pain
• Muscle weakness/swelling
• Dark ("tea-colored") urine (from myoglobinuria)

The full triad is seen in <10% of cases; most patients present with non-specific symptoms (fatigue, malaise, low urine output).

Features of AKI

• Oliguria or anuria
• Rising creatinine and BUN
• Fluid overload, hyperkalemia, metabolic acidosis

Diagnosis

Key Laboratory Findings

• Creatine kinase (CK): >5× upper limit of normal (usually >1,000 IU/L; often much higher)
• Myoglobinuria: Dipstick positive for blood, but no RBCs on microscopy (false positive due to myoglobin)
• Elevated serum creatinine
• Electrolyte abnormalities: Hyperkalemia, hyperphosphatemia, hypocalcemia (early), hyperuricemia

Criteria for AKI (KDIGO)

• Increase in serum creatinine by ≥0.3 mg/dL within 48 hours;
• OR ≥1.5× baseline within 7 days;
• OR urine output <0.5 mL/kg/h for 6 hours

Other Investigations

• Urinalysis: Pigmented granular casts, positive for heme without RBCs
• ECG: To monitor for hyperkalemia
• Assess for causes: Drug screens, infection workup, trauma assessment

Differential Diagnosis

• Other causes of pigment nephropathy (e.g., hemolysis/hemoglobinuria)
• Pre-renal AKI (volume depletion)
• Acute tubular necrosis (ATN) from other causes

Management of Rhabdomyolysis-Induced AKI

Main Principles

• Early and aggressive intravenous fluid resuscitation
• Correction of electrolyte imbalances
• Monitor and support renal function
• Address underlying cause (e.g., trauma, toxin removal)

A. Fluid Therapy

• Start as early as possible—even before CK or myoglobin results
• Typical: Isotonic saline at 1–2 L/hour initially (titrate to urine output)
• Goal: Maintain urine output >200–300 mL/hour
• Avoid potassium-containing fluids

B. Adjunctive Measures

• Alkalinization of urine (sodium bicarbonate infusion): May help prevent myoglobin precipitation in tubules, but evidence is mixed【4】.
• Mannitol diuresis: Sometimes used as osmotic diuretic; not routinely recommended.
• Monitor for complications: Hyperkalemia, hypocalcemia, hyperphosphatemia, fluid overload

C. Dialysis

• Indicated for refractory hyperkalemia, severe metabolic acidosis, fluid overload, or uremic symptoms

Prevention

• Rapid identification and treatment of patients at risk (trauma, surgery, prolonged immobilization)
• Avoid nephrotoxic agents (NSAIDs, contrast)
• Correct hypovolemia early

Prognosis

• Prognosis depends on severity, comorbidities, and speed of treatment.
• Most patients who survive the acute episode and do not require dialysis recover full renal function.
• Mortality: Higher in critically ill, those who develop severe AKI, or with multi-organ failure【2】【5】.

Bullet Point Summary

• Rhabdomyolysis is muscle breakdown leading to release of myoglobin, which is nephrotoxic and causes AKI in 15–50% of cases.
• AKI results from myoglobin-induced tubular injury, hypovolemia, and tubular obstruction.
• Classic presentation: muscle pain, weakness, dark urine, rising creatinine.
• Diagnosis: high CK, myoglobinuria, acute rise in creatinine.
• Immediate and aggressive IV fluids are mainstay of therapy.
• Dialysis may be required in severe or refractory cases.
• Early recognition and treatment prevent progression to severe AKI.

Key Takeaways

• AKI is the most life-threatening complication of rhabdomyolysis.
• Early volume resuscitation is the single most important intervention.
• Monitor for life-threatening electrolyte disturbances (esp. hyperkalemia).
• Outcomes are good with prompt recognition and treatment.

References

1. Bosch X, Poch E, Grau JM. Rhabdomyolysis and acute kidney injury. N Engl J Med. 2009;361(1):62–72. DOI:10.1056/NEJMra0801327
2. Chavez LO, Leon M, Einav S, Varon J. Beyond muscle destruction: a systematic review of rhabdomyolysis for clinical practice. Crit Care. 2016;20:135. Link
3. Vanholder R, Sever MS, Erek E, Lameire N. Rhabdomyolysis. J Am Soc Nephrol. 2000;11(8):1553–1561. Link
4. Petejova N, Martinek A. Acute kidney injury due to rhabdomyolysis and renal replacement therapy: a critical review. Crit Care. 2014;18(3):224. Link
5. Melli G, Chaudhry V, Cornblath DR. Rhabdomyolysis: an evaluation of 475 hospitalized patients. Medicine (Baltimore). 2005;84(6):377–385. Link