A condition characterised by SPASM of muscle, usually caused by a fall in blood CALCIUM levels. This results in hyperexcitability of muscles which may go into spasm at the slightest stimulus. This is well demonstrated in two of the classical signs of the disease: Chvostek's sign, in which the muscles of the face contract when the cheek is tapped over the facial nerve as it emerges on the cheek; and Erb's sign, in which muscles go into spasm in response to an electrical stimulus which normally causes only a brief contraction of the muscle. Tetany can occur in premature newborn babies who may have a low level of calcium, and in children as a result of RICKETS; it also occurs after excessive vomiting, or certain forms of NEPHRITIS. It may also be due to lack of the active principle of the PARATHYROID glands. Treatment consists of the administration of calcium salts, and in severe cases this is done by giving calcium gluconate intravenously or intramuscularly. High doses of vitamin D are also required. HYPERVENTILATION which may occur in acute anxiety, when very fearful or when overbreathing by choice – for example during labour – may also be a cause; the excessive expiration results in loss of carbon dioxide. In turn this increases the degree to which calcium in the blood is bound to albumin, so producing tetany. Treatment is by getting the patient to breathe in and out of a closed bag. This allows build-up of carbon dioxide in the bag, which is rebreathed, so increasing its blood level.