Tetany (medical sign)
Tetany is a medical sign
Medical sign
A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....

 consisting of the involuntary contraction of muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

s, which may be caused by disease or other conditions that increase the action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

 frequency. Muscle cramps that are caused by the disease tetanus
Tetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani...

 are not classified as tetany; rather, they are due to a blocking of the inhibition to the neurons that supply muscles.


Low calcium levels in the bloodstream increase the permeability of neuronal membranes to sodium ions, causing a progressive depolarization, which increases the possibility of action potentials. If the plasma Ca2+ decreases to less than 50% of the normal value of 9.4 mg/dl, action potentials may be spontaneously generated, causing contraction of peripheral skeletal muscles.


  • The usual cause of tetany is lack of calcium
    Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

    . An excess of phosphate
    A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

     (high phosphate-to-calcium ratio) can also trigger the spasms. Milk-and-alkali tetany
    Milk-and-alkali tetany
    Milk-and-alkali tetany is a form of tetany cramps of the wrists and hands or legs caused by an electrolyte imbalance....

     is an example of this imbalance.
  • Underfunction of the parathyroid gland can lead to tetany.
  • Low levels of carbon dioxide
    Carbon dioxide
    Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

     cause tetany by altering the albumin
    Albumin refers generally to any protein that is water soluble, which is moderately soluble in concentrated salt solutions, and experiences heat denaturation. They are commonly found in blood plasma, and are unique to other blood proteins in that they are not glycosylated...

     binding of calcium such that the ionised (physiologically influencing) fraction of calcium is reduced; the most common reason for low carbon dioxide levels is hyperventilation
    Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...

  • Low levels of magnesium
    Hypomagnesemia is an electrolyte disturbance in which there is an abnormally low level of magnesium in the blood. Usually a serum level less than 0.7 mmol/L is used as reference. The prefix hypo- means low . The middle 'magnes' refers to magnesium...

     can lead to tetany.
  • Clostridium tetani
    Clostridium tetani
    Clostridium tetani is a rod-shaped, anaerobic bacterium of the genus Clostridium. Like other Clostridium species, it is Gram-positive, and its appearance on a gram stain resembles tennis rackets or drumsticks. C. tetani is found as spores in soil or in the gastrointestinal tract of animals. C...

     toxin, via inhibition of glycine
    Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...

    -mediated and GABA
    Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...

    -ergic neurotransmission
    Neurotransmission , also called synaptic transmission, is the process by which signaling molecules called neurotransmitters are released by a neuron , and bind to and activate the receptors of another neuron...

    , may lead to tetany.
  • Rebirthing-Breathwork
    Rebirthing-breathwork is a breathing technique that claims to heal suppressed emotions such as anger, fear, sadness, etc. It shares a common belief with various other therapies called rebirthing, with both groups believing that human birth is a traumatic event and that reviewing or revisiting this...

    , purposeful rapid breathing for one - two hours at a time; first causing hyperventilation, may cause tetany.

An excess of potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 in grass hay
Hay is grass, legumes or other herbaceous plants that have been cut, dried, and stored for use as animal fodder, particularly for grazing livestock such as cattle, horses, goats, and sheep. Hay is also fed to pets such as rabbits and guinea pigs...

 or pasture
Pasture is land used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep or swine. The vegetation of tended pasture, forage, consists mainly of grasses, with an interspersion of legumes and other forbs...

 can trigger winter tetany, or grass tetany
Grass tetany
Grass tetany or hypomagniesemic tetany is a metabolic disease of dairy cows grazing on lush pastures, of rapidly growing grass, especially in early spring....

, in ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...



French Professor Armand Trousseau
Armand Trousseau
Armand Trousseau was a French internist. His contributions to medicine include Trousseau sign of malignancy, Trousseau sign of latent tetany, Trousseau-Lallemand bodies , and the truism, "use new drugs quickly, while they still work."-Biography:A native of Tours, Indre-et-Loire, Armand Trousseau...

 (1801-1867) devised the trick (now known as the Trousseau sign of latent tetany
Trousseau sign of latent tetany
Trousseau sign of latent tetany is a medical sign observed in patients with low calcium. This sign may become positive before other gross manifestations of hypocalcemia such as hyperreflexia and tetany, but is generally believed to be more sensitive than the Chvostek sign for hypocalcemia.To...

) of occluding the brachial artery
Brachial artery
The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...

 by squeezing to trigger cramps in the fingers. Also, tetany can be demonstrated by tapping anterior to the ear, at the emergence of the facial nerve. This is now known as the Chvostek sign
Chvostek sign
The Chvostek sign is one of the signs of tetany seen in hypocalcemia. It refers to an abnormal reaction to the stimulation of the facial nerve. When the facial nerve is tapped at the angle of the jaw , the facial muscles on the same side of the face will contract momentarily because of...


Tetany is characterized by contraction of distal muscles of the hands (carpal spasm with extension of interphalangeal joints and adduction and flexion of the metacarpophalangeal joints) and feet (pedal spasm) and is associated with tingling around the mouth and distally in the limbs.

EMG studies reveal single or often grouped motor unit discharges at low discharge frequency during tetany episodes.

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