In a patient with tumor lysis syndrome presenting with nausea, vomiting, palpitations, and muscle aches, which electrolyte abnormality is most likely responsible?

A - Hyperkalemia

In a patient with tumor lysis syndrome presenting with nausea, vomiting, palpitations, and muscle aches, hyperkalemia is the electrolyte abnormality responsible for this specific constellation of symptoms. 1

Why Hyperkalemia Explains This Clinical Picture

Cardiac Manifestations

• Palpitations arise directly from hyperkalemia-induced cardiac electrical disturbances, including arrhythmias, ventricular tachycardia, and fibrillation, as the elevated potassium disrupts normal myocardial conduction. 12
• The American Society of Clinical Oncology emphasizes that hyperkalemia is the most hazardous acute complication of TLS, capable of causing sudden death from cardiac arrhythmias. 23

Neuromuscular Effects

• Muscle aches and cramps represent the neuromuscular dysfunction caused by high potassium concentrations affecting skeletal muscle membrane potentials. 12
• These symptoms occur alongside generalized muscle weakness and paresthesias as potassium levels rise. 1

Gastrointestinal Symptoms

• Nausea and vomiting are common manifestations of TLS-related hyperkalemia, though less specific than the cardiac and neuromuscular findings. 2

Why the Other Options Are Incorrect

Hypocalcemia (Option B)

• Hypocalcemia in TLS typically produces tetany, seizures, carpopedal spasm, and positive Chvostek/Trousseau signs—not palpitations or muscle weakness. 12
• The European Hematology Association guidelines specify that asymptomatic hypocalcemia does not require treatment, and symptomatic hypocalcemia manifests as neuromuscular irritability rather than the described symptom pattern. 24

Hyperuricemia (Option C)

• Hyperuricemia primarily causes renal complications through uric acid crystal deposition in tubules, leading to oliguria and acute renal failure. 15
• It does not generate the cardiac arrhythmias (palpitations) or neuromuscular symptoms (muscle aches) characteristic of this patient's presentation. 1

Hypomagnesemia (Option D)

• Hypomagnesemia is not a cardinal feature of tumor lysis syndrome, which is defined by hyperkalemia, hyperphosphatemia, hypocalcemia, and hyperuricemia. 16
• This electrolyte abnormality does not explain the clinical syndrome described. 1

Critical Clinical Context

Mortality Risk

• Clinical TLS with significant hyperkalemia carries an 83% mortality rate compared to 24% in patients without clinical TLS. 1
• In Burkitt's lymphoma cohorts, two of four deaths were directly attributable to hyperkalemia, underscoring its life-threatening nature. 1

Pathophysiology

• Rapid tumor cell lysis releases massive amounts of intracellular potassium (normal intracellular concentration is 140 mEq/L) into the bloodstream. 17
• Concurrent renal failure impairs potassium excretion, creating a perfect storm for severe hyperkalemia. 14

Immediate Management Priorities

Do not await laboratory confirmation when the clinical picture strongly suggests hyperkalemia—initiate empiric treatment immediately to avoid fatal delays. 1

• Continuous ECG monitoring to detect life-threatening arrhythmias promptly. 24
• Rapid intravenous insulin (0.1 U/kg) with 25% dextrose (2 mL/kg) to shift potassium intracellularly. 12
• Calcium carbonate (100-200 mg/kg per dose) to stabilize myocardial cell membranes and prevent ventricular fibrillation or cardiac arrest. 12
• Prepare for emergency hemodialysis if hyperkalemia persists despite medical therapy or if the patient becomes hemodynamically unstable. 14