Acute Rhabdomyolysis

Related Subjects: | Acute Kidney Injury | Acute Rhabdomyolysis

⚡ Rhabdomyolysis = skeletal muscle breakdown → release of myoglobin → renal tubular deposition. 🔎 Classic clue: Urinalysis shows “+ blood” but no RBCs on microscopy (myoglobinuria).

🔢 Conversion (handy lab equivalents)

• Ca²⁺ 10 mg/dL = 2.5 mmol/L
• Ca²⁺ 12 mg/dL = 3.0 mmol/L
• Ca²⁺ 14 mg/dL = 3.5 mmol/L
• Creatinine 0.8 mg/dL = 70 µmol/L
• Creatinine 1.2 mg/dL = 106 µmol/L
• Creatinine 1.4 mg/dL = 123 µmol/L

📖 About

• 💥 Muscle breakdown → myoglobin release → AKI.
• 🧪 Can cause DIC, ARDS, multi-organ failure.
• ⬆️ CK + muscle enzymes (AST, LDH, aldolase).

🧬 Aetiology

• Myoglobin = O₂-binding protein in skeletal muscle.
• Destruction of ~100 g muscle enough to trigger rhabdo.
• Excess Mb overwhelms plasma proteins → filtered into tubules → cytotoxic + ROS generation.

☠️ Harm Mechanisms

• 🚽 Tubular obstruction from Mb + Tamm-Horsfall casts.
• 🧨 Heme group → oxidative stress + ROS injury.

🩸 Causes

• 🚑 Trauma, crush injuries, prolonged immobility
• 🏋️ Severe exercise, seizures
• 🔥 NMS, malignant hyperthermia
• 💊 Cocaine, heroin, alcohol, statins ± fibrates
• ☠️ CO, methanol, ethylene glycol
• 🩺 Ischaemic limb, compartment syndrome
• 🧬 Polymyositis, metabolic myopathies (e.g. carnitine deficiency)
• 🐍 Snake bites, toxins, caffeine, aspirin
• ⚡ Electrolyte disorders: hypokalaemia, hypophosphataemia
• 🩸 DKA, HONK, sepsis

🧍 Clinical Features

• 💪 Muscle pain, swelling, tenderness
• 🟤 Dark “tea-coloured” urine
• 🪤 Skin necrosis, trauma history
• 🤕 Weakness, drug/toxin history
• 🌡️ Fever, rigidity in NMS

🔍 Investigations

• 💉 CK:
  • Normal ~40–200 U/L
  • ⚪ Mild: 1,000–5,000 (low AKI risk)
  • 🟡 Moderate: 5,000–15,000 (AKI risk)
  • 🔴 Severe: >15,000 (dialysis risk)
• Urine: +blood, no RBCs 🧪
• U&E: AKI, ↑ creatinine
• ↓ Ca²⁺, ↓ phosphate, ↓ K⁺
• ↑ LDH, AST, aldolase, Mb
• MRI useful for muscle damage
• ECG/troponin if cardiac involvement

📊 McMahon Score (≥6 = renal failure risk)

• 📅 Age ≥50, 👩 female sex
• 💉 Creatinine >2.2 mg/dL = 3 pts
• Ca²⁺ <7.5 mg/dL = 2 pts
• Phosphate >5.4 mg/dL = 3 pts
• Bicarbonate <19 = 2 pts
• CK >40,000 = 2 pts
• Non-benign cause (not seizure/exercise/statins/myositis) = 3 pts

🛠️ Management

• 🩺 ABC, treat hyperkalaemia + hypovolaemia
• 💧 Early aggressive fluids (<6h) → aim urine >100 mL/hr
• ⚠️ Elderly: cautious fluids
• 🧪 NaHCO₃ infusion → urinary pH >7.5 (if severe)
• 🚽 Catheter for monitoring
• 💊 Dantrolene/bromocriptine if NMS
• ✂️ Fasciotomy if compartment syndrome
• 🔪 Plastics/surgical review if necrosis
• 🔗 Revascularise ischaemic limb
• 🩸 Nephrology input if worsening renal failure (dialysis)

📚 Reference

• Rhabdomyolysis Review Article

🧑‍⚕️ Case Examples - Acute Rhabdomyolysis

• Case 1 (Trauma-related): 🚑 A 28-year-old man is trapped under rubble after a road traffic accident for 6 hours. On rescue, he has swollen painful thighs, dark “tea-coloured” urine, and oliguria. Bloods: CK 35,000 U/L, K+ 6.5 mmol/L, creatinine rising. Analysis: Prolonged muscle compression → muscle breakdown → release of myoglobin, potassium, phosphate. Risk of acute kidney injury (AKI) and hyperkalaemia-induced arrhythmia. Diagnosis: Crush injury–induced rhabdomyolysis. Management: Aggressive IV fluids (to maintain urine output >200 mL/hr), IV calcium gluconate + insulin/dextrose for hyperkalaemia, consider haemofiltration if renal failure.
• Case 2 (Drug-induced): 💊 A 55-year-old man on high-dose simvastatin presents with diffuse muscle pain, weakness, and cola-coloured urine. Bloods: CK 18,000 U/L, creatinine 220 µmol/L, potassium 5.9 mmol/L. Analysis: Statin-induced myopathy progressing to rhabdomyolysis, worsened by interacting macrolide antibiotic. Diagnosis: Statin-induced rhabdomyolysis. Management: Stop statin and interacting drug, IV fluids, monitor electrolytes and renal function. Treat hyperkalaemia if severe.
• Case 3 (Exertional / Heat-related): 🏃‍♂️🔥 A 22-year-old army recruit collapses after intense training in hot weather. He reports severe muscle cramps, weakness, and passing very dark urine. Bloods: CK 20,000 U/L, urate raised, phosphate raised. Analysis: Exertional heat illness with rhabdomyolysis due to muscle overuse and dehydration. Diagnosis: Exertional rhabdomyolysis. Management: Rapid IV rehydration, electrolyte correction, cooling measures. Avoid nephrotoxic drugs (NSAIDs, contrast).