Chvostek sign

**Technique:** Tap the facial nerve (CN VII) about 2 cm anterior to the earlobe, below the zygomatic arch, over the parotid gland. A positive response is ipsilateral contraction of facial muscles. Grades range from twitching of the lip corner (mildest) to the nose, eyelid, and all facial muscles (most severe).

**Pathophysiology:** Extracellular Ca²⁺ stabilizes voltage-gated Na⁺ channels by shielding negative surface charges on the membrane. In hypocalcemia, this stabilizing effect is lost. The threshold for depolarization drops, so peripheral nerves fire spontaneously or with minimal stimulation. This produces neuromuscular hyperexcitability (tetany). Ionized (free) Ca²⁺ is the active fraction. Alkalosis (for example, hyperventilation) increases albumin binding of Ca²⁺ and lowers ionized Ca²⁺, which can produce the same signs.

**Causes of hypocalcemia (key associations):** - Hypoparathyroidism, most often postsurgical (thyroidectomy, parathyroidectomy) or autoimmune - DiGeorge syndrome (22q11 deletion; third and fourth pharyngeal pouch defects) - Vitamin D deficiency, or CKD with low calcitriol and high phosphate - Acute pancreatitis (fat saponification) - Hypomagnesemia (impairs PTH secretion and action) - Pseudohypoparathyroidism (PTH resistance; high PTH, Albright hereditary osteodystrophy) - Massive transfusion (citrate chelation), rhabdomyolysis, tumor lysis syndrome, and hungry bone syndrome - Loop diuretics

**Related signs:** - **Trousseau sign:** carpopedal spasm after inflating a BP cuff above systolic pressure for about 3 minutes. It is more specific and more sensitive than Chvostek sign. - Perioral and fingertip paresthesias, muscle cramps, laryngospasm, and seizures - **ECG:** prolonged QT interval, which risks torsades de pointes - Chronic hypocalcemia: cataracts, basal ganglia calcifications, and dry skin

**Test characteristics (high-yield):** Chvostek sign is less specific than Trousseau sign. It is positive in about 10–25% of healthy people, so a positive result alone is not diagnostic. It can also be absent in true hypocalcemia. Interpret it alongside serum ionized calcium, PTH, Mg²⁺, phosphate, and vitamin D.

**Management:** Treat the underlying cause. For symptomatic or severe hypocalcemia (tetany, seizures, QT prolongation), give IV calcium gluconate with cardiac monitoring. Replete magnesium if it is low. Chronic treatment is oral calcium plus vitamin D (calcitriol).

**Eponym:** Named for Czech-Austrian physician František Chvostek (1835–1884). Do not confuse it with Trousseau sign of hypocalcemia, which is distinct from Trousseau sign of malignancy (migratory thrombophlebitis).