Primary hyperparathyroidism can be caused by the following:
• Adenomas (80%); may be associated with MEN 1
• Parathyroid hyperplasia (15%)
°° Characterized by diffuse enlargement of all 4 glands; the enlarged glands are usually composed of chief cells
°° Parathyroid carcinoma is very rare
• Hyperparathyroidism can also occur as a paraneoplastic syndrome of lung and renal cell carcinomas.
The excess production of parathyroid hormone (PTH) leads to hypercalcemia, with lab studies showing elevated serum calcium and PTH.
Primary hyperparathyroidism is often asymptomatic, but may cause kidney stones, osteoporosis and osteitis fibrosa cystica, metastatic calcifications, or neurologic changes.
Secondary hyperparathyroidism is caused by any disease that results in hypocalce-mia, leading to increased secretion of PTH by the parathyroid glands; it can result from chronic renal failure, vitamin D deficiency, or malabsorption.
Hypoparathyroidism can result from the surgical removal of glands during thy-roidectomy, DiGeorge syndrome, or a hereditary autoimmune syndrome caused by mutations in the autoimmune regulator gene AIRE. Patients present with muscle spasm and tingling of toes and lips. The hypocalcemia may also cause psychiatric disturbances and cardiac conduction defects (ECG: prolonged QT interval).
Treatment of hypoparathyroidism is vitamin D and calcium.
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