Causes of primary hyperparathyroidism include parathyroid adenomas, hyperplasia of the para-thyroid gland, and certain carcinomas. Secondary hyperparathyroidism is an adaptive response to hypocalcemia produced by conditions such as kid-ney failure or intestinal malabsorption syndromes. Ectopic hyperparathyroidism is due to production of PTH by rare tumors outside the parathyroid gland. Parathyroid hormone–related peptide may cause significant hypercalcemia when secreted by a carci-noma (eg, bronchogenic [lung] carcinoma or hepa-toma). Bone invasion with osteolytic hypercalcemia may complicate multiple myeloma, lymphoma, or leukemia. Overall, the most common cause of hyper-calcemia in hospitalized patients is malignancy. Nearly all clinical manifestations of hyperparathy-roidism are due to hypercalcemia (Table 34–7). Rarer causes of hypercalcemia include bone metas-tases of solid organ tumors, vitamin D intoxication, milk-alkali syndrome, lithium therapy, sarcoidosis, and prolonged immobilization. The treatment of hyperparathyroidism depends on the cause, but sur-gical removal of all four glands is often required in the setting of parathyroid hyperplasia. When there is a single adenoma, its removal cures many patients with sporadic primary hyperparathyroidism.
In patients with hypercalcemia due to hyperpara-thyroidism, hydration with normal saline and diure-sis facilitated by furosemide will usually decrease serum calcium to acceptable values (<14 mg/dL, 7 mEq/L, or 3.5 mmol/L). More aggressive therapy with the intravenous bisphosphonates pamidronate (Aredia) or etidronate (Didronel) may be neces-sary for patients with hypercalcemia of malignancy.
Plicamycin (Mithramycin), glucocorticoids, calcito-nin, or dialysis may be necessary when intravenous bisphosphonates are not sufficient or are contraindi-cated. Hypoventilation should be avoided, as acidosis increases ionized calcium. Elevated calcium levels can cause cardiac arrhythmias. The response to NMBs may be altered in patients with preexisting muscle weakness caused by the effects of calcium at the neuromuscular junction. Osteoporosis worsened by hyperparathyroidism predisposes patients to vertebral compression and bone fractures during anesthetic procedures, positioning, and transport. The notable postoperative complications of parathyroidectomy are similar to those for subtotal thyroidectomy.
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