The usual cause of tetany is lack of calcium. But excess of phosphate can also trigger the spasms. Hypoparathyroidism (hyposecretion of parathormone) can lead to tetany. In this, some skeletal muscles, usually of hands and feet fail to relax after a contraction and remain in sustained condition. Tetany of laryngeal, thoracic and phrenic muscles which help in breathing causes death, because the patient fails to breath (asphyxia).