Tetany

Muscle cramps caused by the disease tetanus are not classified as tetany; rather, they are due to a lack of inhibition to the neurons that supply muscles. Tetanic contractions (physiologic tetanus) have a broad range of muscle contraction types, of which tetany is only one.

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.^{[citation needed]}

• The usual cause of tetany is a deficiency of calcium. An excess of phosphate (high phosphate-to-calcium ratio) can also trigger the spasms.^[2][3]
• Underfunction of the
  parathyroid
  gland can lead to tetany.
• Low levels of carbon dioxide cause tetany by altering the albumin binding of calcium such that the ionized (physiologically influencing) fraction of calcium is reduced; one common reason for low carbon dioxide levels is hyperventilation.^[4]
• Low levels of magnesium can lead to tetany.^[5][6]
• Clostridium tetani toxin, via inhibition of glycine-mediated and GABA-ergic neurotransmission, may lead to tetany.^{[verification needed]}

• An excess of potassium in grass hay or pasture can trigger winter tetany, or grass tetany, in ruminants.^{[verification needed]}
• Osteomalacia and rickets due to deficiency of vitamin D ^{[verification needed]}

Metabolic alkalosis with hypokalemia like Gitelman syndrome and Bartter syndrome can cause tetany. Vomiting induced alkalosis and hyperventilation induced respiratory alkalosis also cause tetany because of neuronal irritability.^{[citation needed]}

French Professor Armand Trousseau (1801–1867) devised the maneuver of occluding the brachial artery by squeezing, to trigger cramps in the fingers. This is now known as the Trousseau sign of latent tetany.^[8]

Also, tetany can be demonstrated by tapping anterior to the ear, at the emergence of the facial nerve. A resultant twitch of the nose or lips suggests low calcium levels. This is now known as the Chvostek sign.^{[citation needed]}

EMG studies reveal single or often grouped motor unit discharges at low discharge frequency during tetany episodes.^{[citation needed]}