On average, a person has four parathyroid glands – two of which are located in the posterior left lobe of the thyroid gland and another two on the posterior of the right lobe. Combined, these four weigh less than 500 mg. Each gland is composed mainly of chief cells, which synthesize and secrete parathyroid hormone or parathormone or PTH for short.
PTH is responsible for resorption of bone in cases of low calcium levels. These hormones tap into the calcium-rich source which is the bone and act on the osteocytes and osteoclast to begin pumping calcium out of the bone and into the extracellular fluid. As with all substances in the body, it is necessary that the body's systems keep a close watch over the balance of PTH and calcium concentrations. An excess of PTH called hyperparathyroidism could cause a weakening of the bones due to excessive calcium and phosphate resorption, while a decrease of which would result in hypoparathyroidism, which could result in tetanic spasms due to a severe deficiency of calcium in the blood.
The development of benign tumors is one of the most common causes of parathyroid disorders. In 90 percent of cases, only one of the glands will develop a tumor while the rest stay happily normal and responsive to changes in the body. The tumor, however, will continue to secrete the hormone regardless of the shift in the balance in the body.
Tumors in the parathyroid are almost always never cancerous. In these glands, the development of cancer is very, very rare. However, the fact that these tumors still produce more parathormone than necessary is genuine cause for worry.
The mechanisms for the development of these tumors are generally unknown. It has been speculated that it may develop due to a genetic factor in much the same way that breast tumors develop. There may be some people who are genetically predisposed to developing the tumors.
The prolonged use of lithium for therapeutic purposes may also cause the development of benign tumors. Among the other possible causes of benign tumors, these cases have a higher risk of developing more than one tumor. Tumors caused by prolonged use of lithium generally show up after 10 to 15 years of therapy.
Another cause is the prolonged use of radioactive iodine as treatment for hyperthyroidism and thyroid cancers. Just like lithium, the tumors develop after a long time – much longer than lithium at 20 years or so. Unlike lithium, however, the prolonged use of radioactive iodine usually causes just one gland to be affected. The other three or so glands remain without tumors most of the time.
This type of disorder is caused by an overgrowth of the glands themselves. Unlike the benign tumors which only affect one or two of the glands, hyperplasia happens simultaneously in all four or more of them. Like benign tumors, however, it has not been fully explained how these glands grow to the degree that they do in parathyroid hyperplasia.
Treatment of hyperplasia involves the removal of most of the glands, leaving just a part of the normal gland behind to continue secreting adequate amounts of parathyroid hormone. This is quite unlike benign tumors, where only one or two glands are removed because in hyperplasia, all four of the glands are causing the problem so your surgeon will have to remove most of them and leave you with just a rather healthy gland to do the necessary work.
Patients with multiple endocrine neoplasia syndrome or MEN may also develop hyperplasia but cases of MEN are very rare. In MEN, hyperplasia develops in patients as young as ten years old. These patients need constant monitoring by a specialist because they could always develop another tumor or hyperplasia even after an operation.
Hereditary Forms of Hyperparathyroidism
Of all the disorders of the parathyroid glands, this is among the rarest, occurring in only about 2 percent of all parathyroid patients. Nearly all of these patients will develop a single adenoma or tumor but most of them will have parathyroid hyperplasia. The difference between hereditary hyperparathyroidism and hyperplasia is that patients with hereditary hyperparathyroidism will almost always develop kidney stones, while those with hyperplasia generally do not.