Chvostek sign
The Chvostek sign (/ˈkvɒstᵻk/) is a clinical sign of existing nerve hyperexcitability (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.
The Trousseau sign of latent tetany is also often used to detect early tetany.
The sign is named after František Chvostek, an Austrian-born surgeon who lived in Moravia, in the Czech Republic. In his professional life, Chvostek devoted himself to the study of etiopathogenesis and to the treatment of neurological disorders, including by means of electrotherapy. In 1876, he first described the sign that bears his name. Later it was independently described by another Austrian physician Nathan Weiss (1851-1883) in 1883.
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