Muscular tetany can be caused by the deficiency of
Parathyroid hormone
Parathormone is secreted by the parathyroid gland. This hormone increases the blood calcium level.
In case of its deficiency, the blood plasma levels of calcium fall significantly. The nerve cells reaching muscles cause frequent stimulation in muscles which leads to the sustained contraction of muscles of feet, hands, larynx etc. which is called muscular tetany.