Rhabdomyolysis

Table of Contents

  1. What is Rhabdomyolysis?
  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. Research Papers
  11. Connections
  12. Featured Videos

What is Rhabdomyolysis?

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 AKI in the United States and is responsible for approximately 26,000 hospitalizations per year. Without aggressive fluid resuscitation, AKI requiring dialysis develops in 10–40% of cases, depending on CK level, volume status, and urine pH.

The classic diagnostic triad is muscle pain and weakness + dark tea-colored urine (myoglobinuria) + markedly elevated serum CK. 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 ATP 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 ATP-dependent calcium pumps (SERCA on the sarcoplasmic reticulum; plasma membrane Ca-ATPase). When ATP 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 ATP 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 AKI 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 CK on routine labs to a catastrophic emergency with AKI, 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 explains why calcium should generally not be administered during the acute phase of rhabdomyolysis unless there is life-threatening hypocalcemia — supplemental calcium worsens the calcium overload in muscle and contributes to the rebound hypercalcemia. The exception is symptomatic tetany or cardiac arrhythmia from hypocalcemia.

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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 AKI, dark urine, or elevated CK after a precipitating event.

Key Laboratory Findings

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Acute Kidney Injury Risk Stratification

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

High-Risk Features for AKI Development

Low-Risk Presentations

CK elevation in the range of 1,000–5,000 IU/L in a well-hydrated young patient with no comorbidities (e.g., mild exertional rhabdomyolysis after intense exercise) has a very low risk of AKI. These patients may be managed with oral hydration, rest, and serial CK monitoring rather than hospitalization, provided they have reliable follow-up and no high-risk features.

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Treatment and Fluid Resuscitation

Aggressive fluid resuscitation is the cornerstone of rhabdomyolysis treatment and has been shown to prevent AKI when initiated early. The goal is to increase urine flow sufficiently to flush myoglobin from the renal tubules before cast formation and oxidative damage become irreversible.

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 IV 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 AKI or dialysis compared to saline alone. The 2019 Kidney Disease: Improving Global Outcomes (KDIGO) guidelines note that evidence is insufficient to recommend routine bicarbonate use. Practice varies by institution. A reasonable approach is to use bicarbonate if urine pH remains below 6.0 despite adequate fluid resuscitation, and to stop bicarbonate if serum pH exceeds 7.45 (risk of worsening symptomatic hypocalcemia by alkalosis).

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 AKI (osmolar gap, volume depletion rebound). Routine use is not recommended; it may be considered in oliguric patients failing to respond to saline alone.

Loop Diuretics

Furosemide and other loop diuretics should generally be avoided in rhabdomyolysis. 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)

Approximately 10–40% of rhabdomyolysis-related AKI patients require renal replacement therapy (hemodialysis or continuous renal replacement therapy/CRRT). Indications are the same as for AKI 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 AKI ultimately recover independent renal function, unlike 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). Hypotensive patients have a lower absolute threshold for intervention. Measurement should not delay fasciotomy when the clinical picture is clear.

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

Recurrent rhabdomyolysis — multiple episodes, often with relatively mild triggers like brief exercise or fasting — should prompt investigation 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). Management: avoid isometric exercise and intense sprinting; aerobic conditioning improves capacity; sucrose ingestion before exercise provides exogenous glucose.

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. Management: avoid prolonged fasting, eat carbohydrate-rich meals before exercise, increase carbohydrate intake during prolonged exercise; medium-chain triglycerides (MCT oil) can serve as an alternative substrate bypassing the CPT system.

Other Metabolic Myopathies

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Research Papers

  1. Bosch X, Poch E, Grau JM. Rhabdomyolysis and acute kidney injury. N Engl J Med. 2009;361(1):62–72. PMID: 19571284
  2. Petejova N, Martinek A. Acute kidney injury due to rhabdomyolysis and renal replacement therapy. Crit Care. 2014;18(3):224. PMID: 25029016
  3. Huerta-Alardín AL, Varon J, Marik PE. Bench-to-bedside review: Rhabdomyolysis — an overview for clinicians. Crit Care. 2005;9(2):158–169. PMID: 15774072
  4. Melli G, Chaudhry V, Cornblath DR. Rhabdomyolysis: an evaluation of 475 hospitalized patients. Medicine (Baltimore). 2005;84(6):377–385. PMID: 16267412
  5. Ward MM. Factors predictive of acute renal failure in rhabdomyolysis. Arch Intern Med. 1988;148(7):1553–1557. PMID: 3382304
  6. Sauret JM, Marinides G, Wang GK. Rhabdomyolysis. Am Fam Physician. 2002;65(5):907–912. PMID: 11898964
  7. Gabow PA, Kaehny WD, Kelleher SP. The spectrum of rhabdomyolysis. Medicine (Baltimore). 1982;61(3):141–152. PMID: 7078398
  8. Simpson JP, Taylor A, Sudhan N, et al. Rhabdomyolysis and acute kidney injury: creatine kinase as a prognostic marker and validation of the McMahon Score in a 10-year cohort. Eur J Emerg Med. 2016;23(5):361–367. PMID: 27145002
  9. Zager RA. Studies of mechanisms and protective maneuvers in myoglobinuric acute renal injury. Lab Invest. 1989;60(5):619–629. PMID: 2724595
  10. 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. PMID: 24018399
  11. 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. PMID: 27900167
  12. Allison RC, Bedsole DL. The other medical causes of rhabdomyolysis. Am J Med Sci. 2003;326(2):79–88. PMID: 12920435

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Connections

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