Most parathyroid tumors are benign.
Parathyroid tumors secrete parathyroid hormone (PTH). Elevated parathyroid hormone levels (hyperparathyroidism) cause hypercalcemia.
Parathyroid adenoma
Parathyroid adenomas are benign tumors that secrete excessive amounts of parathyroid hormone (PTH), leading to hyperparathyroidism which causes hypercalcemia, hypophosphatemia, and excessive bone resorption (leading to osteoporosis).
Parathyroid adenomas are most often isolated solitary adenomas and are more common among older females. However, parathyroid adenoma may occur as part of a hereditary syndrome in patients with multiple endocrine neoplasia.
Most parathyroid adenomas do not cause symptoms and are identified when blood tests done for another reason reveal elevated calcium levels. Symptoms of hyperparathyroidism may occur and are usually due to hypercalcemia or kidney stones.
Diagnosis of hyperparathyroidism is based on the presence of an elevated PTH level in patients with hypercalcemia. In patients with elevated levels of PTH, further testing is needed, including measurement of calcium and phosphorus levels and imaging to evaluate bone density and determine the presence of kidney stones.
Localization of parathyroid tissue before surgery on the parathyroid(s) is sometimes done, especially when minimally invasive surgery is planned. Several techniques have been used, and all are highly accurate:
High-resolution CT with or without CT-guided biopsy
MRI
High-resolution ultrasound
Digital subtraction angiography
Technetium-99 sestamibi scanning
Sestamibi-single photon emission computed tomography (SPECT or MIBI-SPECT)
Technetium-99 sestamibi, a radionuclide agent for parathyroid imaging, is more sensitive and specific than other agents and may be useful for identifying solitary adenomas.
MIBI SPECT (sestamibi-single photon emission computed tomography) gives a 3 dimensional sestamibi scan that improves the ability to localize ectopic glands compared with planar sestamibi scans.
Treatment is usually surgical removal of the affected parathyroid gland. Parathyroid surgery should done by a surgeon experienced in operating on the parathyroid glands.
Occasionally, the calcimimetic, cinacalcet, is given to decrease secretion of PTH.
Parathyroid cancer
Parathyroid cancer is rare.
Risk factors for parathyroid cancer include:
Radiation therapy to the neck
Family history of parathyroid tumors
Parathyroid carcinomas cause hyperparathyroidism similar to adenomas except that the hyperparathyroidism and hypercalcemia due to parathyroid carcinoma is more severe. Calcium levels of 14 to15 mg/dL (3.5 to 3.7 mmol/L) should raise concern for carcinoma.
Symptoms are due to hypercalcemia.
Diagnosis includes blood tests to detect elevated levels of PTH and imaging tests to locate tumors.
Genetic screening of family members in select cases can be performed.
Parathyroid cancers are usually removed surgically. Sometimes radiation therapy and/or chemotherapy are also needed.
Parathyroid carcinomas are usually slow growing. If the initial surgery is able to remove the entire gland without rupture of the capsule, long-term survival without recurrence is common. Recurrent cancer is usually slow growing and spreads locally in the neck. Occasionally, parathyroid cancers are more aggressive with distant metastases.
Discovery of a number of mutations in established cancer genes in parathyroid carcinoma cells suggests targeted therapeutic agents developed for other types of cancers may be useful. Unsuspected germline mutations have also been discovered in a minority of patients with parathyroid cancer (1, 2).
References
1. Sharretts JM, Simonds WF. Clinical and molecular genetics of parathyroid neoplasms. Best Pract Res Clin Endocrinol Metab. 2010;24(3):491-502. doi:10.1016/j.beem.2010.01.003
2. Shattuck TM, Välimäki S, Obara T, et al. Somatic and germ-line mutations of the HRPT2 gene in sporadic parathyroid carcinoma. N Engl J Med. 2003;349(18):1722-1729. doi:10.1056/NEJMoa031237
Key Points
Parathyroid tumors secrete parathyroid hormone (PTH) causing hyperparathyroidism and hypercalcemia.
Parathyroid adenomas are most often isolated solitary adenomas but sometimes occur with other endocrine tumors as part of a multiple endocrine neoplasia syndrome.
Parathyroid cancers cause hyperparathyroidism and hypercalcemia that is often more severe than with adenomas.
Surgical resection is often curative for both parathyroid adenoma and carcinoma.
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