The Chvostek’s sign is a clinical finding characterized by an involuntary contraction or twitch of the facial muscles. This physical reaction is provoked by gently tapping a specific point on the face. It serves as a bedside indicator of increased neuromuscular excitability, suggesting that peripheral nerves are unusually sensitive to mechanical stimulation. The sign acts as a diagnostic clue, pointing toward a possible systemic imbalance that affects nerve function and electrolyte balance.
How the Chvostek’s Sign is Elicited
Eliciting the Chvostek’s sign is a straightforward physical examination maneuver. The technique involves locating the path of the facial nerve (Cranial Nerve VII) on the side of the face. This nerve passes approximately two centimeters anterior to the external ear canal and just below the zygomatic arch.
The clinician then applies a gentle tap or percussion over this location, often using a fingertip or a reflex hammer. A positive result is confirmed if the mechanical stimulus triggers a transient, unilateral spasm or twitch of the facial muscles on the same side. This contraction typically involves the muscles around the eye (orbicularis oculi) and those around the mouth and nose (orbicularis oris). This twitch indicates that the underlying nerve is abnormally irritable and has a lowered threshold for firing an impulse.
The Primary Condition Indicated
A positive Chvostek’s sign is most commonly associated with hypocalcemia, a deficiency of calcium ions in the blood serum. Calcium is a tightly regulated mineral whose concentration must be maintained for normal bodily functions. Hypocalcemia is typically defined as a corrected serum total calcium level below 8.8 milligrams per deciliter or a low ionized calcium level.
This low calcium state can arise from several underlying medical issues. The most frequent cause is hypoparathyroidism, which is a reduced function of the parathyroid glands. These glands produce parathyroid hormone (PTH), which regulates calcium levels. When PTH levels are low, the body cannot absorb enough calcium from the diet or release it from bone stores, leading to a deficit.
Hypocalcemia can also result from severe vitamin D deficiency, as vitamin D is necessary for the intestinal absorption of dietary calcium. Chronic kidney disease can impair the conversion of inactive vitamin D into its active form, further contributing to low calcium levels. Other causes include low magnesium levels, which interfere with PTH release, and conditions that shift the body’s acid-base balance, such as respiratory alkalosis.
Understanding Nerve Hyperexcitability
The facial muscle twitch observed in Chvostek’s sign is a manifestation of neuromuscular hyperexcitability, caused by the low concentration of calcium ions in the blood. Calcium ions play a primary role in stabilizing the electrical potential of nerve cell membranes. These ions bind to voltage-gated sodium channels embedded within the nerve membrane.
The binding of calcium ions to these channels makes it more difficult for the nerve cell to spontaneously depolarize and fire an electrical impulse. When extracellular calcium drops, fewer ions are available to bind and stabilize the channels. This lack of stabilization effectively lowers the nerve’s threshold for activation.
As a result, the nerve cell membrane becomes more permeable to sodium ions, causing the cell to reach its firing potential more easily. The nerve becomes hypersensitive to any external stimulus, such as the mechanical tap used to elicit the sign. This heightened irritability leads to the uncontrolled, involuntary contraction of the facial muscles, often described as latent tetany.
Clinical Confirmation and Treatment
While the Chvostek’s sign offers a quick clinical suspicion of hypocalcemia, diagnosis requires laboratory confirmation to determine the severity and underlying cause. The initial step is to measure the serum calcium level, which is usually corrected for blood albumin concentration. Measuring the ionized calcium level provides the most accurate assessment of the biologically active calcium available in the blood.
Further blood tests investigate the cause of the deficiency, including measuring parathyroid hormone (PTH) levels and the active and inactive forms of vitamin D. These results help distinguish between issues with the parathyroid glands, nutritional deficiency, or kidney problems. For example, a low calcium level paired with a low PTH level strongly suggests hypoparathyroidism.
Treatment for hypocalcemia depends on the severity of symptoms and the underlying cause. Patients with acute, severe symptoms require immediate intervention with intravenous calcium, typically administered as calcium gluconate. For chronic or milder cases, management involves oral calcium supplements, often ranging from 1500 to 2000 milligrams per day. The underlying cause must also be addressed, which may involve prescribing active vitamin D metabolites or PTH replacement therapy for chronic hypoparathyroidism.