Hyperkalemia is the Primary Cause
The muscle weakness, palpitations, and body ache in this patient with Tumor Lysis Syndrome (TLS) after chemotherapy are caused by hyperkalemia, not hypocalcemia. This represents a life-threatening emergency requiring immediate ECG monitoring and aggressive treatment to prevent cardiac arrest.
Why Hyperkalemia Causes These Symptoms
Hyperkalemia produces this exact symptom constellation in TLS patients through its effects on cardiac and neuromuscular function. 1 The rapid release of massive intracellular potassium from lysed tumor cells—particularly within 12-72 hours after chemotherapy initiation—overwhelms the body's excretory capacity and causes:
- Cardiac manifestations: Palpitations, arrhythmias, ventricular tachycardia, and potential cardiac arrest 2
- Neuromuscular effects: Muscle weakness, muscle cramps, and paresthesias 2
- Body aches: Generalized musculoskeletal discomfort from elevated potassium levels 1
This clinical presentation demands immediate assessment before progression to fatal arrhythmias. 1
Why Not Hypocalcemia
Hypocalcemia in TLS typically causes a distinctly different symptom pattern—tetany and seizures—rather than the muscle weakness and palpitations described here. 2 The European Hematology Association guidelines specifically distinguish hypocalcemia's presentation (tetany, seizures) from hyperkalemia's presentation (the symptoms in this case). 1
Furthermore, asymptomatic hypocalcemia does not require treatment in TLS, whereas symptomatic hyperkalemia requires urgent intervention. 2
The Mortality Risk
Clinical TLS with significant hyperkalemia carries an 83% mortality rate versus 24% without clinical TLS. 1 In one Burkitt's lymphoma cohort, two of four deaths were directly attributable to hyperkalemia. 1 This underscores why recognizing hyperkalemia as the cause is critical for survival.
Immediate Management Algorithm
Step 1: Obtain immediate ECG monitoring to detect cardiac arrhythmias from hyperkalemia. 1 Careful ECG monitoring should be performed in all hyperkalemic patients. 2
Step 2: Classify severity and treat accordingly:
For Severe Hyperkalemia (≥6 mmol/L or symptomatic):
- Rapid insulin (0.1 units/kg) plus glucose (25% dextrose 2 mL/kg) to shift potassium intracellularly 2
- Calcium carbonate 100-200 mg/kg/dose to stabilize myocardial cell membranes 2
- Sodium bicarbonate to correct acidosis 2
- Emergency hemodialysis if persistent or life-threatening 1, 3
For Mild Hyperkalemia (<6 mmol/L, asymptomatic):
- Aggressive hydration with loop diuretics to enhance renal excretion 2
- Sodium polystyrene sulfonate 1 g/kg orally or by enema 2
Critical Pitfall to Avoid
Do not aggressively treat hypocalcemia with calcium in the presence of hyperphosphatemia, as this can precipitate calcium-phosphate crystals in renal tubules and worsen kidney injury. 2 Only treat hypocalcemia if symptomatic (tetany, seizures) with a single cautious dose of calcium gluconate 50-100 mg/kg. 2