The positive Chvostek sign is a specific clinical finding used by healthcare professionals to assess a patient’s overall neuromuscular excitability. This physical marker suggests a heightened sensitivity of the nervous system, often indicating a state known as latent tetany. The presence of this sign indicates that the body’s mineral balance may be altered and prompts further diagnostic investigation into conditions that increase nerve and muscle irritability.
Eliciting the Positive Chvostek Sign
The Chvostek sign is named after Austrian physician Franz Chvostek, who first described the phenomenon in 1876. To test for the sign, a healthcare provider performs a simple physical maneuver that stimulates the facial nerve (Cranial Nerve VII). The provider gently taps the patient’s cheek over the nerve’s path, typically located just in front of the earlobe and slightly below the cheekbone (zygomatic arch).
A positive result is characterized by an involuntary, brief twitching or spasm of the facial muscles on the same side of the face as the tap. This muscle contraction can vary in intensity, appearing as a slight flicker of the corner of the mouth, the nose, or the eyelid. The mechanical stimulus deliberately excites the nerve, revealing an underlying hyper-excitability not otherwise apparent in a resting state. The facial twitching confirms the motor neuron is reacting abnormally to a minimal stimulus.
The Role of Calcium in Neuromuscular Excitability
The physiological basis for a positive Chvostek sign centers on the concentration of calcium ions in the blood, specifically low calcium levels (hypocalcemia). Calcium plays a fundamental role in stabilizing the membranes of nerve cells and muscles throughout the body. These positively charged calcium ions normally bind to the outside surface of voltage-gated sodium channels on nerve membranes, which initiate nerve signals.
By binding to these channels, calcium acts like a brake, making it more difficult for the sodium channels to open and fire a nerve impulse. When the concentration of extracellular calcium drops, this stabilizing effect is reduced or lost, essentially taking the brake off the nervous system. This lowered threshold means the nerve requires much less stimulation to fire an action potential, leading to hyper-excitability.
The motor nerves become overly sensitive to even minor mechanical stimulation, such as the light tap used in the Chvostek test. This increased electrical excitability causes the spontaneous and involuntary muscle contractions seen in the face, which is a localized manifestation of the body’s overall neuromuscular irritability.
Underlying Causes and Clinical Significance
A positive Chvostek sign serves as a clinical red flag that prompts immediate investigation into the patient’s serum calcium levels. The most common cause of hypocalcemia leading to this sign is hypoparathyroidism, a condition resulting from insufficient production of parathyroid hormone, often following thyroid or neck surgery. Other potential causes include severe Vitamin D deficiency, which impairs calcium absorption, and chronic kidney failure, which disrupts the balance of calcium and phosphate.
The sign can also appear in acute conditions like severe acute pancreatitis, where calcium is sequestered in the abdomen, or in cases of hypomagnesemia, as magnesium is necessary for proper parathyroid hormone function. Because a positive Chvostek sign may also be present in a small percentage of healthy individuals, its clinical significance is always interpreted alongside a patient’s medical history and laboratory blood tests.
Confirmation of hypocalcemia necessitates prompt treatment to correct the mineral imbalance, often involving intravenous calcium salts and oral supplements like Vitamin D or calcitriol. Unmanaged severe hypocalcemia can lead to serious systemic complications, including painful, sustained muscle spasms (tetany), laryngospasm, and even seizures. The presence of the sign guides medical professionals toward a timely diagnosis and intervention to prevent these neurological events.