Rhabdomyolysis

Rhabdomyolysis — scientific infographic poster

Table of Contents

  1. How Rhabdomyolysis Works
  2. Causes and Risk Factors
  3. Pathogenesis: From Muscle Death to Kidney Injury
  4. Symptoms and Clinical Presentation
  5. Diagnosis and Laboratory Findings
  6. Acute Kidney Injury Risk Stratification
  7. Treatment and Fluid Resuscitation
  8. Compartment Syndrome and Fasciotomy
  9. Genetic and Metabolic Forms
  10. Key Research Papers
  11. Connections
  12. Featured Videos

How Rhabdomyolysis Works

Rhabdomyolysis is a potentially life-threatening syndrome caused by the breakdown (lysis) of skeletal muscle cells, releasing their intracellular contents — most critically myoglobin, creatine kinase (CK), potassium, phosphate, and uric acid — into the bloodstream. The word comes from Greek: rhabdo (rod-shaped), myo (muscle), and lysis (breakdown), reflecting the rod-shaped appearance of skeletal muscle fibers.

The hallmark complication is acute kidney injury (AKI): myoglobin released from destroyed muscle cells is freely filtered by the glomerulus, but at high concentrations it precipitates in the renal tubules, causing direct tubular toxicity through oxidative injury and physical obstruction. Rhabdomyolysis accounts for 5–7% of all cases of acute kidney injury in the United States and is responsible for approximately 26,000 hospitalizations per year. How often the kidneys fail badly enough to need dialysis depends on how sick the group studied was. Among 2,371 hospital patients whose creatine kinase was above 5,000 U/L, 8.0% needed dialysis or another form of renal replacement therapy and 14.1% died in hospital (McMahon et al., 2013). In a 10-year series of 232 intensive-care patients with confirmed rhabdomyolysis, 45 (19%) developed acute kidney injury and 29 (12.5%) needed dialysis, and death was far more common in those who did (62% versus 18%) (Simpson et al., 2016).

The classic diagnostic triad is muscle pain and weakness + dark tea-colored urine (myoglobinuria) + markedly elevated serum creatine kinase. However, fewer than half of patients with confirmed rhabdomyolysis present with all three components simultaneously — particularly in exertional or drug-induced cases where the presentation may be subtle.

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Causes and Risk Factors

Rhabdomyolysis has a remarkably diverse array of causes, unified by the common mechanism of skeletal muscle cell membrane disruption. Understanding the cause is essential because it dictates not only acute treatment but prevention of recurrence.

Traumatic Causes

Exertional Causes

Drugs and Toxins

Electrolyte and Metabolic Causes

Infections

Inflammatory and Autoimmune Causes

Inflammatory myopathies — polymyositis, dermatomyositis, immune-mediated necrotizing myopathy (IMNM, sometimes statin-triggered) — cause chronic myositis that can flare into acute rhabdomyolysis. IMNM associated with anti-SRP or anti-HMGCR antibodies can present as acute rhabdomyolysis and requires immunosuppression, not simply statin discontinuation.

Malignant Hyperthermia

A rare but potentially lethal pharmacogenetic disorder triggered by volatile anesthetic agents (halothane, sevoflurane, desflurane) or succinylcholine in genetically susceptible individuals. Mutations in the ryanodine receptor gene (RYR1) or dihydropyridine receptor cause uncontrolled sarcoplasmic reticulum calcium release in skeletal muscle → massive hypermetabolism + rigidity + hyperthermia + rhabdomyolysis. Treated emergently with dantrolene.

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Pathogenesis: From Muscle Death to Kidney Injury

Regardless of the triggering cause, muscle cell death in rhabdomyolysis follows a common pathway centered on loss of cellular energy and uncontrolled calcium influx into the muscle cell.

Step 1: Muscle Cell Adenosine Triphosphate Depletion and Calcium Overload

Normal skeletal muscle cells tightly regulate intracellular calcium at concentrations approximately 10,000-fold lower than extracellular calcium. This gradient is maintained by adenosine triphosphate-dependent calcium pumps (SERCA on the sarcoplasmic reticulum; plasma membrane Ca-ATPase). When adenosine triphosphate production fails — from ischemia, toxins, infections, or metabolic depletion — these pumps fail. Sodium and calcium pour into the cell through non-selective cation channels. Intracellular calcium activates destructive enzymes: phospholipases (degrade membrane phospholipids), proteases (including calpain, which degrades cytoskeletal proteins), and mitochondrial permeability transition pores (causing irreversible mitochondrial damage and further adenosine triphosphate depletion). This creates a self-amplifying cycle that ends in cell death.

Step 2: Intracellular Contents Released into Circulation

Disruption of the muscle cell plasma membrane releases the cell's contents into the interstitium and then the bloodstream:

Step 3: Myoglobin-Induced Acute Kidney Injury

Myoglobin causes acute kidney injury through three complementary mechanisms:

  1. Direct tubular toxicity: Myoglobin is filtered at the glomerulus and reabsorbed in the proximal tubule. When present in high concentrations, the heme group of myoglobin undergoes oxidation to generate reactive oxygen species (ROS), particularly in acidic urine, directly damaging proximal and distal tubular epithelial cells. The Fe3+ (ferrihemate) form is the most nephrotoxic — it generates lipid peroxidation of tubular cell membranes.
  2. Tubular obstruction: Myoglobin precipitates with Tamm-Horsfall protein (uromodulin) in the distal tubule and collecting duct, forming dense brown casts that physically obstruct urine flow. Acidic urine and concentrated urine dramatically accelerate precipitation — explaining why alkaline urine and high urine output protect the kidney.
  3. Renal vasoconstriction: Myoglobin scavenges nitric oxide in the renal vasculature, causing afferent arteriolar vasoconstriction and reducing glomerular filtration. Volume depletion (common in crush and exertional cases) synergistically worsens this effect.

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Symptoms and Clinical Presentation

The clinical presentation of rhabdomyolysis spans a wide spectrum — from an asymptomatic incidental finding of elevated creatine kinase on routine labs to a catastrophic emergency with acute kidney injury, cardiac arrhythmias, and disseminated intravascular coagulation (DIC).

Classic Triad (Present Together in <50% of Cases)

Signs of Severe or Complicated Rhabdomyolysis

Delayed Hypercalcemia in Recovery

A clinically important but counterintuitive phenomenon: after the acute phase, calcium that deposited in necrotic muscle tissue during the injury phase is remobilized as damaged muscle is cleared, causing rebound hypercalcemia in the recovery phase (days 1–3 after the acute event). This is why calcium is held back during the acute phase unless the low calcium is itself life-threatening: extra calcium adds to the calcium already overloading the muscle and feeds the rebound high calcium that follows. Tetany (painful muscle spasms) with symptoms, or an abnormal heart rhythm from the low calcium, are the situations in which it is given.

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Diagnosis and Laboratory Findings

Diagnosis is based on clinical context plus laboratory confirmation. A high index of suspicion is required in any patient with unexplained acute kidney injury, dark urine, or elevated creatine kinase after a precipitating event.

Key Laboratory Findings

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Acute Kidney Injury Risk Stratification

Not all rhabdomyolysis leads to acute kidney injury. Risk stratification helps guide the intensity of monitoring and aggressiveness of fluid resuscitation.

High-Risk Features for Acute Kidney Injury Development

A score worked out on the day of admission does better than creatine kinase alone. The McMahon score combines age, sex, the cause of the muscle damage, and the first measurements of creatinine, creatine kinase, phosphate, calcium and bicarbonate. It was built from 2,371 hospital patients whose creatine kinase exceeded 5,000 U/L, and in the validation group 2.3% of people with a score below 5 died or needed dialysis against 61.2% of those with a score above 10. The outcome also depended heavily on the cause: worst after cardiac arrest (58.5%), compartment syndrome (41.2%) and sepsis (39.3%), and mildest after exercise (3.2%), seizures (6.0%) and myositis (1.7%) (McMahon et al., 2013). In the Cambridge cohort a McMahon score of 6 or more on admission was 86% sensitive and 68% specific for needing dialysis, which was both earlier and more accurate than waiting for the creatine kinase peak (Simpson et al., 2016).

Low-Risk Presentations

Creatine kinase elevation in the range of 1,000–5,000 international units/L in a well-hydrated young patient with no comorbidities (e.g., mild exertional rhabdomyolysis after intense exercise) has a very low risk of acute kidney injury. Such patients are often managed out of hospital with fluids by mouth, rest and repeat creatine kinase measurements, when follow-up is reliable and none of the high-risk features above is present.

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Treatment and Fluid Resuscitation

Fluid resuscitation is the cornerstone of rhabdomyolysis treatment, started as early as possible. The goal is to increase urine flow sufficiently to flush myoglobin from the renal tubules before cast formation and oxidative damage become irreversible.

How thin the evidence is for everything else was set out by a 2019 Danish intensive-care guideline (DASAIM/DSIT), which graded all of the evidence low or very low quality and issued eight weak recommendations and no strong ones. It suggests early rather than late fluids, and crystalloid fluids (such as saline) rather than colloids; it suggests against the routine use of loop diuretics, against mannitol, against any diuretic as routine, against alkalinisation with sodium bicarbonate, and against routine renal replacement therapy as a preventive measure (Michelsen et al., 2019).

Intravenous Fluid Resuscitation

Isotonic saline (0.9% NaCl) is the standard first-line fluid. The target urine output is 200–300 mL/h (roughly 3 mL/kg/h in adults) — a rate roughly four to six times normal urine output, designed to achieve continuous tubular flushing. Achieving this target typically requires large volumes: 10–15 liters (or more) per day in the first 24–48 hours for severe rhabdomyolysis. Careful monitoring for fluid overload is essential, particularly in patients with pre-existing cardiac or renal disease.

Urine Alkalinization with Sodium Bicarbonate

The theoretical basis is compelling: alkaline urine (pH >6.5) inhibits myoglobin precipitation in tubular fluid, reduces heme-mediated oxidative injury, and decreases uric acid crystal formation. Some centers add sodium bicarbonate (50 mEq per liter of intravenous fluid) with the goal of maintaining urine pH above 6.5. However, the clinical evidence is mixed — no randomized controlled trial has demonstrated that bicarbonate addition reduces the rate of acute kidney injury or dialysis compared to saline alone. The 2019 Danish intensive-care guideline (DASAIM/DSIT) states: "We suggest against routine use of alkalinisation with sodium bicarbonate" — a weak recommendation based on low-quality evidence. Practice varies by institution: where bicarbonate is used, it is typically added when urine pH stays below 6.0 despite adequate fluids and stopped if blood pH rises above 7.45, because alkalosis makes symptoms of low calcium worse.

Mannitol

Mannitol has been proposed as an adjunct because of its osmotic diuretic effect (increases tubular flow) and free-radical scavenging properties. However, no randomized trial supports its use, and it carries risks in acute kidney injury (osmolar gap, volume depletion rebound). The 2019 Danish guideline suggests against using mannitol; some units still try it when urine output stays low despite saline alone.

Loop Diuretics

The 2019 Danish guideline suggests against the routine use of loop diuretics such as furosemide in rhabdomyolysis, and against the routine use of any diuretic. They increase urine flow but also acidify tubular fluid (by exchanging H+ for sodium), potentially worsening myoglobin precipitation. Additionally, diuretics can worsen volume depletion if the patient is not adequately filled.

Electrolyte Management

Renal Replacement Therapy (Dialysis)

In the two largest published cohorts, 8.0% of 2,371 hospital patients with a creatine kinase above 5,000 U/L needed renal replacement therapy (McMahon et al., 2013), and 12.5% of 232 intensive-care patients with confirmed rhabdomyolysis did (Simpson et al., 2016) — hemodialysis or continuous renal replacement therapy (CRRT). The 2019 Danish guideline suggests against starting dialysis routinely as a preventive measure. The reasons for starting it are the same as for acute kidney injury in general: severe hyperkalemia refractory to medical management, severe metabolic acidosis, volume overload unresponsive to diuretics, and uremia with encephalopathy. Recovery of renal function is common — the majority of patients who need dialysis for rhabdomyolysis acute kidney injury ultimately recover independent renal function, unlike chronic kidney disease (CKD) patients on chronic dialysis.

Cause-Specific Management

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Compartment Syndrome and Fasciotomy

Compartment syndrome is both a cause and a complication of rhabdomyolysis — muscle swelling from rhabdomyolysis can itself raise intra-compartmental pressure, creating a dangerous cycle. It requires urgent surgical intervention and is the most time-critical aspect of rhabdomyolysis management.

Recognition

The "5 P's" of acute compartment syndrome are: Pain (out of proportion to the injury, especially with passive stretch), Pressure (tense, woody swelling), Paresthesias (tingling/numbness from nerve ischemia — an early sign), Paralysis (late sign indicating nerve/muscle death), and Pulselessness (very late, ominous — arterial involvement). Crucially, pulse may be present even with severe compartment syndrome because arterial pressure exceeds compartment pressure while capillary/venous perfusion is already compromised.

Measurement and Threshold

Compartment pressure is measured with a needle manometer or electronic device inserted into the affected compartment. A pressure above 30 mmHg is the standard surgical threshold, as is a pressure within 30 mmHg of the diastolic blood pressure (the delta-P or perfusion pressure method). Patients with low blood pressure cross that threshold at a lower absolute pressure. When the clinical picture is already clear, surgery goes ahead without waiting for a measurement.

Fasciotomy

Fasciotomy — surgical opening of the fascial compartment to release pressure — is the definitive treatment. In the lower leg (the most common site), four-compartment fasciotomy through two longitudinal incisions releases all four compartments (anterior, lateral, superficial posterior, deep posterior). Fasciotomy wounds are left open for 48–72 hours to allow swelling to resolve, then closed primarily or with split-thickness skin grafting. Outcomes are markedly better when fasciotomy is performed within 6 hours of compartment pressure elevation; delay beyond 12 hours significantly increases permanent nerve and muscle damage.

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Genetic and Metabolic Forms

Repeated episodes of rhabdomyolysis — several attacks, often with relatively mild triggers such as brief exercise or going without food — are what leads to testing for an underlying metabolic myopathy. These disorders reveal the normal physiology of muscle energy metabolism and are important because they are often manageable once identified.

McArdle Disease (Glycogen Storage Disease Type V)

McArdle disease is caused by biallelic mutations in the PYGM gene encoding myophosphorylase — the muscle-specific enzyme that breaks down glycogen to glucose-1-phosphate for glycolysis. Patients cannot mobilize muscle glycogen, so muscles cannot sustain anaerobic exercise. Presentation: exercise intolerance from childhood, premature fatigue and cramps with brief intense effort (isometric exercise or sprinting), with a characteristic "second wind" phenomenon — after 10–15 minutes of sustained aerobic exercise, symptoms paradoxically improve as fatty acid oxidation and hepatic gluconeogenesis compensate for the absent glycogenolysis. Forearm ischemic exercise test shows absent lactate rise with normal ammonia rise (confirming myophosphorylase deficiency without nerve/cardiac involvement). What is described for this condition: isometric effort (holding a heavy load still) and intense sprinting are what bring on the attacks, aerobic conditioning improves exercise capacity, and sugar (sucrose) taken before exercise supplies glucose the muscle cannot release from its own glycogen.

Carnitine Palmitoyltransferase II (CPT-II) Deficiency

The most common inherited cause of recurrent exertional rhabdomyolysis in adults. CPT-II is the inner mitochondrial membrane enzyme that transfers long-chain fatty acyl groups from the cytoplasm into the mitochondrial matrix for beta-oxidation. Without CPT-II, muscles cannot use long-chain fatty acids as fuel during prolonged exercise. Triggers are characteristically prolonged submaximal exercise + fasting (the combination depletes both glycogen and blood glucose, maximally forcing the muscle to depend on fatty acid oxidation that is blocked). Patients are often exercise-tolerant for short bursts. Diagnosis: muscle biopsy showing CPT-II deficiency; genetic testing. What is described for this condition: long periods without food and long exercise on an empty stomach are what trigger attacks, carbohydrate before and during prolonged exercise supplies the fuel the muscle can still use, and medium-chain triglycerides (MCT oil) provide an alternative fuel that bypasses the blocked CPT system.

Other Metabolic Myopathies

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Key Research Papers

  1. Bosch X, Poch E, Grau JM. Rhabdomyolysis and acute kidney injury. N Engl J Med. 2009;361(1):62–72. — PubMed PMID: 19571284
  2. Petejova N, Martinek A. Acute kidney injury due to rhabdomyolysis and renal replacement therapy: a critical review. Crit Care. 2014;18(3):224. — PubMed PMID: 25043142
  3. Michelsen J, Cordtz J, Liboriussen L, et al. Prevention of rhabdomyolysis-induced acute kidney injury — a DASAIM/DSIT clinical practice guideline. Acta Anaesthesiol Scand. 2019;63(5):576–586. — PubMed PMID: 30644084
  4. Huerta-Alardín AL, Varon J, Marik PE. Bench-to-bedside review: Rhabdomyolysis — an overview for clinicians. Crit Care. 2005;9(2):158–169. — PubMed PMID: 15774072
  5. Melli G, Chaudhry V, Cornblath DR. Rhabdomyolysis: an evaluation of 475 hospitalized patients. Medicine (Baltimore). 2005;84(6):377–385. — PubMed PMID: 16267412
  6. Ward MM. Factors predictive of acute renal failure in rhabdomyolysis. Arch Intern Med. 1988;148(7):1553–1557. — PubMed PMID: 3382301
  7. Sauret JM, Marinides G, Wang GK. Rhabdomyolysis. Am Fam Physician. 2002;65(5):907–912. — PubMed PMID: 11898964
  8. Gabow PA, Kaehny WD, Kelleher SP. The spectrum of rhabdomyolysis. Medicine (Baltimore). 1982;61(3):141–152. — PubMed PMID: 7078398
  9. Simpson JP, Taylor A, Sudhan N, Menon DK, Lavinio A. Rhabdomyolysis and acute kidney injury: creatine kinase as a prognostic marker and validation of the McMahon Score in a 10-year cohort: a retrospective observational evaluation. Eur J Anaesthesiol. 2016;33(12):906–912. — PubMed PMID: 27259093
  10. Zager RA. Studies of mechanisms and protective maneuvers in myoglobinuric acute renal injury. Lab Invest. 1989;60(5):619–629. — PubMed PMID: 2716281
  11. McMahon GM, Zeng X, Waikar SS. A risk prediction score for kidney failure or mortality in rhabdomyolysis. JAMA Intern Med. 2013;173(19):1821–1828. — PubMed PMID: 24000014
  12. Scalco RS, Snoeck M, Quinlivan R, et al. Exertional rhabdomyolysis: physiological response or manifestation of an underlying myopathy? BMJ Open Sport Exerc Med. 2016;2(1):e000151. — PubMed PMID: 27900193
  13. Allison RC, Bedsole DL. The other medical causes of rhabdomyolysis. Am J Med Sci. 2003;326(2):79–88. — PubMed PMID: 12920439

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Connections

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