The
Chvostek sign 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 Ca
2+ with a normal calcium level due to a shift of Ca
2+ from the blood to
albumin which has become more negative in the alkalotic state.