The positive Chvostek sign is a clinical finding used as a physical assessment tool for neuromuscular irritability. Named after the 19th-century Austrian surgeon Franz Chvostek, the sign was first described in patients experiencing latent tetany. The test is a simple, non-invasive method for a clinician to assess the excitability of a patient’s peripheral nerves. A positive result indicates a heightened state of nerve sensitivity, often linked to a mineral imbalance within the body.
How the Chvostek Sign is Elicited
Eliciting the Chvostek sign involves a straightforward physical maneuver performed by a healthcare professional. The patient is typically relaxed, and the head is positioned comfortably to allow easy access to the side of the face being examined. The clinician locates the path of the facial nerve (Cranial Nerve VII), which emerges near the ear.
The testing location is usually about two centimeters in front of the earlobe, situated just below the zygomatic arch, or cheekbone. The clinician delivers a gentle, sharp tap over this precise point using a fingertip or a reflex hammer. This action provides a minor mechanical stimulus directly to the underlying facial nerve trunk.
A response is considered positive if the tapping causes an involuntary contraction or twitching of the facial muscles on the same side of the face. This spasm can range from a slight twitch around the mouth to a more pronounced contraction involving the muscles around the nose or the eyelid. The presence of any visible, ipsilateral facial muscle contraction following the tap is interpreted as a positive Chvostek sign.
Clinical Meaning of a Positive Result
A positive Chvostek sign is traditionally associated with hypocalcemia, meaning low levels of calcium circulating in the blood. This reduction in calcium concentration can severely disrupt normal physiological functions. While the sign points toward neuromuscular hyperexcitability, it is not perfectly reliable, as studies show it can be present in up to 25% of healthy individuals with normal calcium levels.
Despite its limitations, the sign remains a valuable clinical indicator, particularly when used in conjunction with other symptoms. Low blood calcium levels can lead to tetany, characterized by painful, involuntary muscle spasms and cramps throughout the body. The Chvostek sign suggests a heightened susceptibility to this severe muscle hyperactivity.
Several underlying conditions can lead to the severe hypocalcemia necessary to provoke this reaction. The most common cause is parathyroid gland dysfunction (hypoparathyroidism), where the glands do not produce enough parathyroid hormone to regulate calcium. This is frequently seen following neck surgery, such as a thyroidectomy, where the parathyroid glands may be inadvertently damaged. Other causes include severe Vitamin D deficiency, which impairs calcium absorption, and chronic kidney disease, which affects calcium processing.
The Role of Calcium in Nerve Function
The physiological basis for the positive Chvostek sign lies in the fundamental role calcium plays in stabilizing the membranes of nerve cells. Nerve impulses, or action potentials, are generated when sodium ions flow rapidly into the nerve cell through voltage-gated sodium channels. These channels are the molecular gates that determine when a nerve will “fire.”
Calcium ions in the fluid surrounding the nerve cell membrane normally bind to the outside surface of these sodium channels. This binding acts as a stabilizer, effectively increasing the amount of electrical stimulation required to open the channels and initiate a nerve impulse. The calcium acts as a kind of brake, keeping the nerve from firing too easily.
When the concentration of calcium in the blood drops, this stabilizing effect is significantly diminished or entirely lost. The voltage-gated sodium channels become unstable and are more sensitive to even minor changes in electrical potential. This effectively lowers the threshold at which the nerve will depolarize.
Consequently, the nerve becomes hyper-excitable, meaning it is prone to discharging spontaneously or in response to a minimal stimulus. The gentle mechanical percussion delivered during the Chvostek test, which would be ignored by a nerve with normal calcium levels, is enough to mechanically deform the nerve membrane and trigger an action potential. This uncontrolled nerve firing causes the corresponding facial muscle to contract, resulting in the characteristic twitch that defines the positive Chvostek sign.