A positive Chvostek’s sign is a clinical finding indicating heightened excitability within the nervous system. This response is primarily associated with hypocalcemia, which describes abnormally low levels of calcium circulating in the blood. While not exclusively diagnostic, the presence of this sign prompts investigation into a potential electrolyte imbalance.
How the Chvostek’s Sign Test is Performed
The Chvostek’s sign is elicited through a straightforward physical examination maneuver involving the facial nerve (Cranial Nerve VII). The examiner identifies the target area just anterior to the patient’s ear and administers a gentle, sharp tap using a fingertip or a reflex hammer. A positive result is confirmed if the stimulation causes an involuntary, brief spasm or twitching of the facial muscles on the same side of the face. This muscular response can range from a slight quiver of the lip to a more noticeable contraction. This twitching is a direct physical manifestation of latent tetany, indicating the facial nerve has become overly sensitive.
The Essential Connection to Hypocalcemia
A positive Chvostek’s sign points toward hypocalcemia because calcium is fundamental to stabilizing nerve cell membranes. Calcium ions interact with and partially block voltage-gated sodium channels, which elevates the threshold required to generate a nerve impulse. In essence, calcium acts as a natural buffer, preventing the nerve from firing too easily.
When calcium concentration drops below the normal range, this stabilizing effect is significantly diminished. The absence of the calcium-mediated block causes the nerve membrane to become highly permeable to sodium ions, lowering the threshold potential required to trigger an electrical impulse. This state of heightened excitability means a minimal stimulus, like the tap during the Chvostek’s test, provokes a spontaneous discharge in the facial nerve. This pathological sensitivity is termed neuromuscular irritability. The Chvostek’s sign is a localized reflection of this systemic hyperexcitability.
Medical Conditions That Trigger Hypocalcemia
A positive Chvostek’s sign is a consequence of an underlying disorder that disrupts calcium homeostasis.
Hypoparathyroidism
The most frequent cause of hypocalcemia is a reduction in parathyroid hormone (PTH) levels, known as hypoparathyroidism. The parathyroid glands regulate calcium, and their accidental damage during neck surgeries, such as a thyroidectomy, is the most common reason for acute postsurgical hypoparathyroidism. A lack of PTH means the body cannot effectively mobilize calcium from bone or promote its reabsorption in the kidneys.
Vitamin D Deficiency
Severe Vitamin D deficiency is another significant cause, as it impairs the body’s ability to absorb calcium from the diet in the intestines. Inadequate sunlight exposure or poor nutritional intake prevents the formation of the active form of Vitamin D necessary for calcium absorption.
Chronic Kidney Disease
Chronic kidney disease also frequently leads to hypocalcemia. The kidneys are responsible for activating Vitamin D into its usable form; when kidney function declines, this activation process is impaired. Additionally, failing kidneys cannot excrete phosphate efficiently, and the resulting high phosphate levels bind to serum calcium, further reducing the amount of free, active calcium available.
Other Factors
Other factors, like hypomagnesemia, also contribute to low calcium levels. Magnesium is required for the secretion and function of parathyroid hormone, so its deficiency can induce a functional hypoparathyroidism. Conditions such as acute pancreatitis, which causes calcium to precipitate with fatty acids, and certain medications can also trigger this electrolyte imbalance.
Addressing the Underlying Cause
A positive Chvostek’s sign indicates that a comprehensive laboratory workup is necessary. The first step is confirming hypocalcemia by measuring serum calcium levels, specifically the ionized calcium. Further blood tests determine the root cause, including measuring parathyroid hormone (PTH), Vitamin D levels, and magnesium. Management focuses entirely on correcting the underlying calcium deficiency.
For acute, symptomatic hypocalcemia, intravenous administration of calcium, usually calcium gluconate, is required to rapidly restore normal nerve function and prevent complications. For chronic or less severe cases, the standard treatment involves oral supplementation with calcium and active forms of Vitamin D. If the cause is hypoparathyroidism, a physician may use recombinant human PTH in refractory cases. The overall goal is to carefully monitor calcium levels and treat the primary disorder to achieve lasting electrolyte balance.