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.

This occurs because calcium ions interact with the exterior surface of sodium channels in the plasma membrane of nerve cells and hypocalcemia effectively increases resting potential (rendering the cells more excitable) since less positive charge is present extracellularly.

[7] 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.

French Professor Armand Trousseau (1801–1867) devised the maneuver of occluding the brachial artery by squeezing, to trigger cramps in the fingers.

[8] Also, tetany can be demonstrated by tapping anterior to the ear, at the emergence of the facial nerve.