Parathyroid Disorders

Hyperparathyroidism

Primary (originating from the parathyroid gland) hyperparathyroidism is most often caused by a parathyroid adenoma (generally benign). Carcinoma of parathyroid gland is quite rare. Parathyroid adenomas can be seen in isolation or as a component of the multiple endocrine neoplasia syndromes (MEN) I or IIa. Clinically, primary hyperparathyroidism can lead to metastatic calcification in soft tissues and calcium stone formation in the kidneys. Further, increased levels of PTH and the resultant hypercalcemia can predispose to peptic ulcers. Secondary hyperparathyroidism is usually caused by advanced kidney disease. Inability of the failing kidney to excrete phosphorus leads to [Page 1337]increased levels of phosphorus in the serum and decreased levels of calcium both of which are a signal for PTH production and release. The parathyroids, under constant stimulation from these electrolyte abnormalities, undergo hyperplasia (growth in the number of cells).

Tertiary hyperparathyroidism is persistent parathyroid hyperfunction in spite of correction of hypocalcemia in preexisting secondary hyperparathyroidism. It is often caused by the development of an adenoma in a previously hyperplastic gland. Hyperparathyroidism may also arise from enzyme deficiencies that are involved in the processing of vitamin D. A discussion of hyperparathyroidism is not complete without a discussion of hypercalcemia, given the direct relationship between PTH levels and serum calcium levels.

Increased levels of serum calcium can be associated with bone pain, kidney stone formation, stomach pain, and psychiatric disturbances. Although rare in cases of parathyroid dysfunction, acutely high levels of calcium necessitate immediate hydration. After hydration and volume restoration is performed, calcium excretion can be achieved with the use of loop diuretics such as furosemide. Parathyroid adenomas can be removed by endocrine surgeons; however, it is prudent to watch serum calcium levels in the postoperative period.

Hypoparathryroidism

Hypoparathryroidism is most commonly caused by accidental surgical excision during removal of the thyroid gland. Care must be taken intraoperatively to identify the parathyroid glands at the time of surgery. Absence of the parathyroid glands may be seen with the congenital disorder DiGeorge syndrome, which is associated with thymic hypoplasia and deletion of chromosome 22q11. Hypoparathyroidism manifests as hypocalcemia. Hypocalcemia can lead to increased neuromuscular excitability and tetany (prolonged, sustained contraction of muscle). This can be tested for in a person with suspected hypocalcemia with the use of Chvostek's sign and Trousseau's sign. The Chvostek maneuver includes tapping the cheek to check for spasm of the muscles of mastication (chewing). Trousseau's maneuver involves inflating a blood pressure cuff over an upper extremity and checking for spasms of muscle movement (referred to as carpopedal spasms). Treatment of hypocalcemia includes prompt and careful replacement of serum calcium usually intravenously.

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