The Chvostek sign (also Weiss sign) is one of the signs of tetany seen in hypocalcemia. It refers to an abnormal reaction to the stimulation of the facial nerve. When the facial nerve is tapped at the angle of the jaw (i.e. masseter muscle), the facial muscles on the same side of the face will contract momentarily (typically a twitch of the nose or lips) because of hypocalcemia (i.e. from hypoparathyroidism, pseudohypoparathyroidism, hypovitaminosis D) with resultant hyperexcitability of nerves. Though classically described in hypocalcemia, this sign may also be encountered in respiratory alkalosis, such as that seen in hyperventilation, which actually causes decreased serum Ca2+ with a normal calcium level due to a shift of Ca2+ from the blood to albumin which has become more negative in the alkalotic state.
It was first described by František Chvostek, a Czecho-Austrian physician in 1876, and later independently by Nathan Weiss in 1883.
The Trousseau sign of latent tetany is also often used to detect early tetany.
Chvostek's sign may also be present in hypomagnesemia, frequently seen in alcoholics, persons with diarrhea, patients taking aminoglycosides or diuretics, because hypomagnesemia can cause hypocalcemia. Magnesium is a cofactor for Adenylate cyclase. The reaction that Adenylate Cyclase catalyzes is the conversion of ATP to 3',5'-cyclic AMP. The 3',5'-cyclic AMP (cAMP) is required for Parathyroid hormone activation.
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