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The Chvostek sign (//) is a clinical signs 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 sign is named after František Chvostek, an Austrian born surgeon in Moravia in the Czech Republic. Chvostek in his professional life he devoted himself to the study of the etiopathogenesis and treatment of neurological disorders, including through the use electrotherapy. He described for the first time in 1876 the sign that bears his name. Later it was independently described by another Austrian physician Nathan Weiss (1851-1883) 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.
Chvostek's sign is found in tetany.
It may also be present in hypomagnesemia, 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. 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 (Ca 2+ ) 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 actual clinical utility of this sign has become reduced.
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