What is it? It is the facial contraction obtained by the distribution of the facial nerve in front of the action of swallowing.
It is caused by the mechanical irritability of the peripheral nerves. It is indicative of hypocalcemia and is the most reliable test for hypocalcemia.
A contraction of the facial muscles after gentle tapping on the facial nerve in front of the ear indicating hyperirritability of the facial nerve.
The Chvostek sign is a clinical indication of hypocalcemia .
It manifests when the doctor hits the facial nerve in the jaw. The sign manifests as a contraction of the nose or lips on the same side. This is due to nerves in the area that is hyperexcited due to lack of calcium.
The presence of the sign may be useful in a differential diagnosis, since it only appears in a few conditions such as hypoparathyroidism and vitamin D overdose.
A simple test used during a physical examination to check for very low levels of calcium in the blood, originally recorded by 19th-century Austrian surgeon Frantisek Chvostek.
The Chvostek sign is considered a classic sign of hypocalcemia.
With this test, the doctor hits the middle cheekbone near the area where the facial nerve is located (where the seventh cranial nerve leaves the salivary parotid gland).
If the person is hypocalcemic, this action will usually cause a contraction similar to that of a complaint in the cheek, nose and corner of the patient’s mouth.
Patients who exhibit the Chvostek sign will need supplemental doses of calcium and will often also need vitamin D supplements to stimulate the additional absorption of calcium from their intestines.
Unfortunately, less than 20-25 percent of patients who do not have hypocalcemia also show some facial contractions with this test. In addition, some patients who do not really have hypocalcemia will not produce the Chvostek sign.
The Chvostek sign is also sometimes positive in the absence of hypocalcemia when patients have other diseases, such as myxedema, rickets, measles, and diphtheria. In addition, some healthy patients may show a positive Chvostek sign.
In the best case, the Chvostek sign is simply a good basic indicator of possible hypocalcemia and should be followed by a blood test of the patient’s calcium levels.
The definition of the Chvostek sign varies in the medical literature, as does the interpretation of the sign. In fact, two methods clearly described to obtain the Chvostek sign have been reported.
The most known version of the sign, or the Chvostek I phenomenon, is described as contraction and / or contracture of the facial muscles.
Produced by hitting the facial nerve at a specific point on the face. This point is located 0.5 to 1 cm below the zygomatic process of the temporal bone, 2 cm before the lobe of the ear, and in a line with the angle of the jaw.
A similar response described, the lesser known Chvostek II, can be produced by touching a different location on the face. This point is located on the line between the zygomatic prominence and the corner of the mouth, a third of the distance from the zygoma.
Signo of Trousseau
The Trousseau-von Bonsdorff test has been correlated with the presence of the Trousseau sign. The Trousseau-von Bonsdorff test is performed immediately after deflating the sphygmomanometer.
The patient is instructed to breathe deeply at a speed of 40 breaths / min and then carefully observe the spasms in the carpopedal previously described.
One study found the Trousseau-von Bonsdorff test as a useful complement to the Trousseau sign when assessing the presence of hypocalcemia
The Trousseau sign is more consistently defined in the medical literature than the Chvostek sign. The sign of Trousseau is presented as a carpopedal spasm that occurs after a few minutes of inflating a sphygmomanometer cuff above the systolic blood pressure.
The occlusion of the brachial artery causes flexion of the wrist and metacarpophalangeal joints, hyperextension of the fingers and flexion of the thumb fingers in the palm, producing the characteristic posture called d’accoucheur .
In addition to the obvious visual manifestations, patients with a positive Trousseau sign may also experience paresthesia of the fingers, muscle fasciculations or contractions of the fingers, and feeling of muscle cramping or stiffness.
The mechanism proposed for the sign of Trousseau is the increased excitability of the nerves in the arm and forearm, ostensibly caused by hypocalcemia, which in turn causes muscle contractions.
These conditions are exacerbated by the ischemia produced by the sphygmomanometer, which results in the spasm that defines the sign.
The sign of Trousseau was observed by the nineteenth-century French physician Armand Trousseau.
Most experts believe that this sign, which uses a blood pressure cuff to cause the characteristic flexion of the wrist and finger joints, is more reliable (sensitive and specific) than the Chvostek sign for hypocalcemic.
As with the Chvostek sign, hypocalcemia is not the only condition that can produce a positive Trousseau sign. Another common clinical entity that is known to cause a positive Trousseau sign is hypomagnesemia.
Because this condition often occurs concomitantly with hypocalcemia, the determination of the electrolyte abnormality responsible for causing the two separate positive responses is difficult.
Comparison of the Sign of Chvostek and the Sign of Trousseau
Although the two signs have never been compared directly, it is believed that the Trousseau sign is more specific for hypocalcemia than the Chvostek sign.
In one study, 94% of patients with confirmed hypocalcemia had a positive Trousseau sign, whereas only 1% of healthy patients showed a positive Trousseau sign. In addition, only 9% of normal patients had a positive Trousseau-von Bonsdorff test.