Tetany, parathyroid deficiency

Hypocalcemia - To correct plasma calcium levels (eg, neonatal tetany and tetany due to parathyroid deficiency, vitamin D deficiency, alkalosis) prevention of hypocalcemia during exchange transfusions conditions associated with intestinal malabsorption. 

Tetany—A deficiency of vitamin D may cause tetany, though it is not the only cause. Tetany may also result from insufficient absorption of calcium or from a disturbance of the parathyroid gland. Tetany is characterized by muscle twitching, cramps, convulsions, and low serum calcium—less than 7 mg per 100 ml. 

Calcium and magnesium deficiency also occur in some patients with the malabsorption syndrome and this may lead to tetany or bone changes. Low blood calcium levels may result from decreased absorption associated with lack of effective compensatory parathyroid activity. In patients in whom secondary hyperparathyroidism is effective, extensive loss of calcium from the bones may occur. The cause of the defective absorption of calcium in patients of the sprue group is complex and not yet fully understood (B3, Dl, Jl, M7, Nl). It is important that complications such as calcium or magnesium deficiency should be corrected before the final steps of definitive diagnosis are attempted. If this is not done, the secondary effects may obscure the results of other tests. 

Calcium gluconate is indicated in hypocalcemia associated with neonatal tetany and tetany due to parathyroid difficulty, vitamin D deficiency, or alkalosis in prevention of tetany during exchange transfusions and in conditions related to malabsorption. 

It is obvious that a variety of disorders would result from a disturbance of the vitamin D endocrine system. Fat malabsorption would result in a deficiency of vitamin D giving rise ultimately to osteomalacia or rickets or secondary hyperparathyroidism. A hepatic disorder such as severe cirrhosis, or biliary atresia, may result in malabsorption of vitamin D and defective vitamin D-25-hydroxylation. Dilantin and phenobarbital cause low plasma 25-OH-D levels resulting in rickets and osteomala-cia246) Qf parathyroid glands would cause a severe hypocalcemia and tetany. 

Removal of the parathyroid glands in dogs, alone or in combination with the thyroid, lowered blood GSH (222-225, 203). During the period of latent tetany, there was a slight decrease, but when manifest signs of tetany developed there was a more abrupt fall (up to 28%) in the blood GSH level (203). The drop in blood GSH was especially marked in those animals which survived the operation for a longer period because of the administration of small doses of parathormone (203), and it was partially restored by treatment with AT-10 (203) or parathormone (222, 203). The studies reported in thyroid-parathyroidectomized dogs (225) are more difficult to interpret because of the combined hormone deficiency. 

Another substance, chemically related to vitamin D2 (calciferol), has an effect similar to that of parathormone. This is dihydrotochysterol (AT 10). The effect is, however, in some aspects more comparable to D-hypervitaminosis. Dihydrotachysterol is used frequently in tetany caused by a deficiency of the parathyroid hormone, because the peptide hormone is not readily available. 

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