The Chvostek sign is a clinical sign of hypocalcemia which consist of twitching of muscles innervated by facial nerve. It refers to an abnormal reaction to the stimulation of the facial nerve. When the facial nerve is tapped in front of the tragus, the facial muscles on the same side of the face will contract momentarily, because of hypocalcemia, 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 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.
Etymology
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, in 1883.
It is obtained by striking with a finger or a hammer a point that is approximately 2 cm in front of the lobe of the ear and about 1 cm below the zygomatic process. Response occurs in the form of ipsilateral contraction of some or all of the muscles innervated by the facial nerve. The effect is the lateral deviation of the labial and nasal fold toward the stimulated side.
Hitting a point between the middle third and upper third of the line joining the angle of the mouth to the zygomatic process gives rise to only a contraction of the muscles of the mouth and nose.
Causes
Chvostek's sign is found in tetany. However, it may also be present in hypomagnesemia. Magnesium is a cofactor for adenylate cyclase, which catalyzes the conversion of ATP to 3',5'-cyclic AMP. The 3',5'-cyclic AMP is required for parathyroid hormone activation. It is frequently seen in alcoholics, persons with diarrhea, patients taking aminoglycosides or diuretics, because hypomagnesemia can cause hypocalcemia. It is also seen in measles, tetanus and myxedema. It can also be found in subjects with respiratory alkalosis, for example as a result of hyperventilation syndrome, which can lead to a drastic reduction of the concentration in serum of calcium ions while at normal levels, for the binding of a significant proportion of ionized calcium with albumin and globulins.
Chvostek's sign is not a very specific sign of tetany as it may be seen in 10% to 25% of healthy adults. It is therefore not a reliable clinical sign for diagnosing latent tetany. The sensitivity is lower than that in the corresponding Trousseau sign as it is negative in 30% of patients with hypocalcemia. Due to the combination of poor sensitivity and specificity the clinical utility of this sign is reduced.
