Thyroid & Adrenal
Commonest cause of hyperparathyroidism is:
|C||Hyperplasia of a single parathyroid gland|
|D||Hyperplasia of all the parathyroid glands|
a. The exact cause of PHPT is unknown, although exposure to low-dose therapeutic ionizing radiation and familial predisposition account for some cases.
b. Various diets and intermittent exposure to sunshine may also be related. Other causes include renal leak of calcium and declining renal function with age, as well as alteration in the sensitivity of parathyroid glands to suppression by calcium.
c. The latency period for development of PHPT after radiation exposure is longer than that for the development of thyroid tumors, with most cases occurring 30 to 40 years after exposure.
d. Patients who have been exposed to radiation have similar clinical presentations and calcium levels when compared to patients without a history of radiation exposure.
e. However, the former tend to have higher PTH levels and a higher incidence of concomitant thyroid neoplasms.
f. Lithium therapy has been known to shift the set-point for PTH secretion in parathyroid cells, thereby resulting in elevated PTH levels and mild hypercalcemia.
g. Lithium stimulates the growth of abnormal parathyroid glands in vitro, and in susceptible patients in vivo. 52 PHPT results from the enlargement of a single gland or parathyroid adenoma in approximately 80% of cases, multiple adenomas or hyperplasia in 15 to 20% of patients and parathyroid carcinoma in 1% of patients.
h. Existence of two enlarged glands or double adenomas is supported by biochemical (calcium and PTH), intraoperative PTH, molecular, and histologic data.
i. This entity is less common in younger patients, but accounts for up to 10% of older patients with primary HPT.
j. It should be emphasized that when more than one abnormal parathyroid gland is identified preoperatively or intraoperatively, the patient has hyperplasia (all glands abnormal) until proven otherwise.