Rhabdomyolysis

Rhabdomyolysis is a syndrome of skeletal muscle breakdown with release of intracellular contents into the circulation, leading to myoglobinuria and potential acute kidney injury. It is a serious complication of compartment syndrome, crush injuries, and other muscle-damaging conditions.

Epidemiology:

• Common complication of compartment syndrome (especially if delayed over 6 hours)
• Crush injuries (earthquakes, building collapse)
• Prolonged immobility (unconscious patients)
• Exercise-induced (exertional rhabdomyolysis)
• Drug-induced (statins, alcohol)
• Heat-related illness

Mechanism of Muscle Breakdown:

Three mechanisms of myoglobinuric AKI (all favoured by hypovolaemia and aciduria):

• Renal vasoconstriction / ischaemia - hypovolaemia plus scavenging of nitric oxide by myoglobin reduces medullary blood flow
• Intratubular cast formation - myoglobin precipitates with Tamm-Horsfall protein, especially in acidic urine (pH under 5.6), obstructing distal tubules
• Direct heme-mediated tubular toxicity - iron-catalysed lipid peroxidation and free-radical injury of proximal tubular cells

History:

• Compartment syndrome (most common orthopaedic cause)
• Crush injury (prolonged compression)
• Prolonged immobility (unconscious patient)
• Exercise-induced (exertional)
• Drug history (statins, alcohol)
• Heat exposure

Physical Examination:

Urine Assessment:

• Color: Dark tea-colored or cola-colored = myoglobinuria
• Dipstick: Positive for blood (but no RBCs on microscopy) = myoglobin
• Output: Decreased output indicates AKI developing

Differential Diagnosis

The "blood-positive dipstick with no red cells" picture and dark urine have a short, high-yield differential. The key discriminator is serum CK and the urine microscopy.

Laboratory Tests:

Monitoring Protocol:

Urinary Sediment Findings

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Note: Rhabdomyolysis itself is a medical condition, not a surgical procedure. However, if compartment syndrome is the underlying cause, fasciotomy is required. This section addresses fasciotomy technique when rhabdomyolysis is present or suspected.

After Fasciotomy (if compartment syndrome cause):

Key Monitoring:

• Urine output (target over 200ml/hr)
• Urine color (should lighten as myoglobinuria resolves)
• CK levels (should decline after 24-48h peak)
• Potassium (hyperkalemia risk)
• Creatinine (AKI progression)

Global epidemiology:

• Crush-related rhabdomyolysis follows mass-casualty events: earthquakes are the archetype (Marmara/Turkey 1999, Wenchuan/China 2008, Haiti 2010, Kahramanmaras/Turkey 2023), where it is a leading cause of preventable post-event death after head injury.
• Non-traumatic causes (statins/drugs, exertion, alcohol, immobility, infection, inherited metabolic myopathies) dominate in routine hospital practice worldwide.
• Acute kidney injury complicates roughly 10-50% of significant rhabdomyolysis depending on cause and resuscitation timing; with early aggressive fluids, AKI and dialysis dependence fall substantially.

Guidelines side by side (where emphasis genuinely differs):

High- vs limited-resource practice variation:

• High-resource: point-of-care CK and electrolytes, continuous ECG, ICU-level monitoring, and ready access to haemodialysis/CRRT for refractory AKI.
• Limited-resource / disaster settings: the decisive intervention is early oral and IV fluid; dialysis capacity is the rate-limiting step. International nephrology task forces pre-position dialysis support after earthquakes precisely because crush AKI overwhelms local capacity.

Much of "classic" rhabdomyolysis management is based on physiology and observational data rather than randomised trials. The exam-relevant debates are:

The etiology table and Scenario 3 both invoke exertional rhabdomyolysis, and the sports-medicine guidance flags screening for "recurrent/atypical cases and inherited metabolic myopathy before return to sport" - but the underlying disease is never developed. This is a distinct, high-yield strand: most exertional cases are self-limiting, but a minority signal a genetic muscle disorder that changes counselling and return-to-play.

Exertional (exercise-induced) rhabdomyolysis typically follows unaccustomed, intense or eccentric exercise, often compounded by heat, humidity, dehydration, sleep deprivation or stimulant/supplement use. Compared with crush injury, CK elevations are usually lower and acute kidney injury is uncommon (McMahon and colleagues found exercise carried one of the lowest rates of dialysis or death). Sickle cell trait is a recognised risk factor for exertional collapse and rhabdomyolysis under extreme exertion, and drugs (statins, especially with fibrates, and alcohol) lower the threshold.

The "Outcomes and Prognosis" section lists prognostic factors qualitatively ("higher CK = worse prognosis", "delayed treatment = higher AKI risk"). The examinable upgrade is that these have been combined into a validated admission risk score that quantifies who needs intensive monitoring and early nephrology.

The McMahon score was derived and validated in 2,371 patients with CK over 5,000 U/L across two Boston teaching hospitals. It combines eight admission variables: age, female sex, initial creatinine, initial CK, phosphate, calcium, bicarbonate, and the cause of rhabdomyolysis (seizure, syncope, exercise, statin or myositis attracting negative/protective weighting versus other causes). It predicts the composite of renal replacement therapy or in-hospital death - not a treatment threshold - with good discrimination (C-statistic about 0.82-0.83).

• A low score (under 5) carried roughly a 2-3% risk of dialysis or death.
• A high score (over 10) carried roughly a 61% risk - a very different level of care.
• Cause dominates outcome: the highest composite-event rates were after cardiac arrest, sepsis and compartment syndrome, while myositis, exercise and seizures carried the lowest.

This reframes the exam answer: rather than fixating on a single CK cut-off, use the whole admission picture - age, renal function, electrolytes and the cause - to decide who is triaged to ICU, early nephrology and closer surveillance.