The Chvostek sign (/ˈkvɒstɪk/) is a clinical sign that someone may have a low blood calcium level (a decreased serum calcium, called hypocalcemia). The Chvostek sign is the abnormal twitching of muscles that are activated (innervated) by the facial nerve (also known as Cranial Nerve Seven, or CNVII).[1] When the facial nerve is tapped in front of the ear, the facial muscles on the same side of the face will contract sporadically (called ipsilateral facial spasm). The muscles that control the nose, lips and eyebrows are often the ones that will spasm.
These facial spasms are caused by the nerves that control the muscle being easily excited (called hyperexcitability) due to hypocalcemia. Hypocalcemia can be caused by many things, including parathyroid conditions (such as when the parathyroid gland does not function well, called hypoparathyroidism) and vitamin diseases (such as a vitamin D deficiency). Sometimes, the Chvostek sign can be caused by other conditions which interfere with the balance of calcium, such as imbalanced acid and alkaline in blood causing respiratory alkalosis (an alkaline blood pH).
The Trousseau sign of latent tetany is another sign of decreased calcium in blood where muscles in the hand contract when the brachial artery supplying the area is occluded. The Trousseau sign of latent tetany also generally occurs earlier than the Chvostek sign and is a more accurate predictor of hypocalcemia, allowing clinicians to recognise the condition earlier.