tetany, condition of mineral imbalance in the body that results in severe muscle spasms. Tetany occurs when the concentration of calcium ions (Ca⁺⁺) in extracellular fluids such as plasma falls below normal. The nervous system becomes increasingly excitable, and nerves discharge spontaneously, sending impulses to skeletal muscles and causing spasmodic contractions. Mild tetany is characterized by tingling in the fingers, toes, and lips; acute tetany, consisting of severe muscular contractions, tremors, and cramps, can result in death. Abnormally low extracellular calcium ion concentration can result from failure of the parathyroid glands to release parathyroid hormone, the substance responsible for the regulation of calcium concentration in the body; a deficiency in vitamin D, which facilitates calcium ion absorption from the gastrointestinal tract; or alkalosis, an excessively alkaline state of body fluids resulting from persistent vomiting, rapid breathing, or excess activity of the hormone aldosterone. Most forms of tetany can be treated with calcium, vitamin D, and a controlled diet. Muscle tetany is also caused by the pathogenic bacterium Clostridium tetani in the disease tetanus.