The Chvostek sign is one of the best-known symptoms of latent tetany. It is also sometimes seen in patients in an anxious state. Learning to check for the sign and understanding its significance can make a big difference in your patient’s health.
The Chvostek (pronounced “vos-tek”) sign is typically detected by registered nurses on their first encounter with a patient. Doctors typically don’t check for this sign, so if the sign is not checked for by a nurse and reported forward, the underlying issue may go unaddressed.
We discuss all there is to know about Chvostek and its relation to the Trousseau sign in this post. You may also want to check out other nursing tips such as identifying HELLP syndrome or performing a BUBBLE HE assessment.
What is Chvostek’s sign?
A positive Chvostek sign is the spasm or twitching of the facial muscles when a healthcare professional gently taps on the patient’s cheek. More specifically, the cheek is tapped about two centimeters from the ear. If twitching occurs, it is a clinical finding indicating low calcium levels in the patient’s blood (hypocalcemia).
The idea behind the tapping of the cheek is to see if the facial nerve has an atypical reaction to the tapping. Normally, the facial nerves don’t twitch on tapping. If there is no twitching, the Chvostek sign is negative for the patient.
However, the pressure put on the facial nerve by the tapping can trigger involuntary contractions of muscles in the area. If the face muscles spasm, the patient has a positive Chvostek sign.
While our understanding of this phenomenon is still limited, what we do know is that ionized calcium controls the neuron’s threshold potential. The threshold potential of a neuron is the point before which a neuron fires.
When there is a low calcium level in a patient’s blood, the threshold potential for neurons is decreased. In other words, neurons fire a lot more easily when stimulated.
Hypocalcemia, therefore, increases the hyperexcitability of nerves in the body. This is what results in the spontaneous spasms of the facial nerves when stimulated by tapping.
Trousseau sign vs Chvostek sign
In clinical medicine, Chvostek’s and Trousseau’s signs are the two most recognized signs of hypocalcemia.
While the Trousseau sign refers to the carpopedal spasm that appears when blood pressure is measured, the Chvostek sign refers to the twitching of the facial muscles when the patient’s cheek is tapped gently.
Side-by-side photographs of both signs were published as an Images in Clinical Medicine feature in the New England Journal of Medicine (Jesus and Landry, 2012).
How to perform the Chvostek sign
To check for the sign, you must tap the patient’s cheek gently, about two centimeters in front of their ear. This spot is just over the facial nerve’s route, and you will be stimulating the seventh cranial nerve.
If you see the periorbital and the mouth muscles, or the muscles close to the eyes twitching, on the same side of the face you’re stimulating, you can consider the patient to have a positive Chvostek sign.
Types of Chvostek sign
The sign is of two types:
Chvostek sign: type I
The type I Chvostek sign is the technique where you use a finger or a hammer to tap about 2cm in front of the ear. If you notice ipsilateral contraction in some or all the muscles that the facial nerve controls, the sign is positive. Bear in mind that the twitching appears on only the stimulated side of the face.
Chvostek sign: type II
The type II Chvostek sign involves gently tapping the region between the middle and upper third of the line that joins the zygomatic process and the mouth.
If the sign is positive, the muscles of the mouth and the nose contract involuntarily.
What does a positive Chvostek sign mean?
As mentioned earlier, a positive Chvostek sign is an indicator of low calcium levels in the body. Hypocalcemia can have several effects on the patient’s body since calcium is responsible for regulating several cellular processes.
Besides neuronal activity, hypocalcemia can affect hormone secretion and blood coagulation.
It is important to note that the parathyroid hormone (PTH), which is released by the body’s parathyroid glands, is responsible for regulating the calcium levels in the body. When the calcium levels in the body drop, PTH is circulated in the body.
In simple words, hypocalcemia commonly results from hypoparathyroidism, which is inadequate production of PTH. Most often this PTH deficit follows thyroid or parathyroid surgery, where the parathyroid glands are removed or their blood supply is damaged. (Hyperparathyroidism is the opposite condition – excess PTH, which raises serum calcium rather than lowering it.)
Hypoparathyroidism can also result from autoimmune disorders and genetic conditions that involve the parathyroid glands.
There are several other factors that can lead to a patient having a positive Chvostek sign:
- Kidney failure
- Acute pancreatitis
- Respiratory alkalosis due to hyperventilation
- Low vitamin D or magnesium levels in the body
- Effect of medicine such as proton pump inhibitors and bisphosphonates
Reliability of the Chvostek sign
In 2013, a study published in Neurology (Méneret et al.) concluded the sign is not a reliable indicator of hypocalcemia. Roughly one in four healthy subjects showed a positive sign, and 29% of patients with hypocalcemia did not show a positive sign. Reported sensitivity is about 26% – it misses most true hypocalcemia – while specificity is high at roughly 96%.
Furthermore, a positive sign can appear due to reasons other than hypocalcemia. This contributes to its overall unreliability.
A larger population-based analysis reinforces the point rather than rescuing the sign. Hujoel’s 2016 study in Neurology: Clinical Practice, using NHANES I data on 3,434 adults aged 25-74, found that the odds of a positive Chvostek sign rose by about 4% for each 1 mg/dL increase in serum calcium – the opposite direction from what the sign is supposed to indicate.
The author’s conclusion was blunt: a positive Chvostek sign is informative of normal to increased serum calcium rather than hypocalcemia.
The practical implication for nursing is straightforward. Treat a positive Chvostek sign as a prompt to check an ionized calcium level, never as a substitute for one. A negative sign does not rule out hypocalcemia, and a positive sign in an otherwise well patient is more likely to be a normal variant. Trousseau’s sign is the more reliable of the two bedside signs.
How did the Chvostek sign get its name?
Researcher Franz Chvostek first described this phenomenon in 1876. The tetany sign was named after him, and he stated that the twitching of the facial nerve is not a body reflex but rather a result of stimulation of the facial nerve.
Another researcher, Shultze, observed that the Chvostek’s sign appears on another part of the face: between the zygomatic arch and the corner of the mouth. However, this mode of stimulation isn’t given a name after its researcher. Instead, it is called Chvostek signs II and III, depending on the extensiveness of the response.
A lot of the time, the Chvostek sign appears in patients in this mode only.
References
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