Trousseau Sign: Definition and Clinical Significance
Trousseau sign is a clinical test for latent tetany caused by neuromuscular hyperexcitability, most commonly due to hypocalcemia, in which inflating a blood pressure cuff above systolic pressure for 3 minutes induces carpopedal spasm—characterized by flexion of the wrist and metacarpophalangeal joints with extension of the interphalangeal joints. 1, 2
Clinical Manifestation
- The classic presentation involves the hand adopting a characteristic "obstetrician's hand" position: wrist flexion, thumb adduction, metacarpophalangeal joint flexion, and interphalangeal joint extension 3
- This spasm occurs because ischemia from cuff inflation increases neuromuscular excitability in patients with underlying electrolyte disturbances 2
- The test is considered positive when this carpopedal spasm develops within 3 minutes of cuff inflation above systolic blood pressure 1
Primary Causes and Pathophysiology
Hypocalcemia is the most common cause, requiring treatment when serum calcium falls below 8.4 mg/dL with clinical symptoms including paresthesia, positive Chvostek's and Trousseau's signs, bronchospasm, laryngospasm, tetany, or seizures 1
Other Electrolyte Disturbances
- Hypomagnesemia can cause positive Trousseau sign and must be corrected, as magnesium deficiency impairs parathyroid hormone secretion and prevents successful calcium correction 1, 2
- Hypokalemia can induce tetany with positive Trousseau sign even in the absence of alkalosis, though this is rare 4
- Metabolic alkalosis increases neuromuscular excitability and can cause tetany with positive Trousseau sign, even with normal calcium levels 3, 5
Diagnostic Workup When Trousseau Sign is Positive
Immediately order ionized calcium (or corrected total calcium), magnesium, parathyroid hormone, phosphorus, creatinine, and 25-hydroxyvitamin D levels to determine both severity and underlying etiology 6
Essential Laboratory Panel
- Ionized calcium is the most accurate measure, with levels below 0.8 mmol/L indicating urgent need for correction due to cardiac dysrhythmia risk 6
- Magnesium level is critical—hypomagnesemia will prevent successful calcium correction regardless of supplementation 6
- Phosphorus and intact PTH help differentiate causes of hypocalcemia 7
- 12-lead ECG to assess for prolonged QT interval, as hypocalcemia can cause cardiac arrhythmias and impaired contractility 6
Corrected Calcium Calculation
- Use the formula: Corrected calcium (mg/dL) = Total calcium (mg/dL) + 0.8 × [4 - Serum albumin (g/dL)] 1
Clinical Companion: Chvostek Sign
- Chvostek sign (facial muscle twitching when tapping the facial nerve anterior to the ear) is another provocative test for latent tetany 2
- Trousseau sign is generally more specific than Chvostek sign for detecting hypocalcemia 3
- Both signs can be positive simultaneously, though Trousseau sign may be positive when Chvostek sign is negative 4, 8
Critical Clinical Pitfalls
- Never assume hypocalcemia is the only cause—tetany with positive Trousseau sign can occur with normocalcemia in the setting of severe metabolic alkalosis, hypophosphatemia, or isolated hypokalemia 3, 4
- Always check magnesium—hypomagnesemia is frequently overlooked and will prevent correction of hypocalcemia 6
- Consider alkalosis—the pH change reduces ionized calcium even when total calcium is normal, and complexing of calcium as calcium bicarbonate further decreases the ionized fraction 5
- Monitor calcium-phosphorus product—maintain below 55 mg²/dL² to prevent dangerous precipitation and soft tissue calcification 1, 6