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- parathyroid gland
hyperparathyroidism
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What is hyperparathyroidism?
Hyperparathyroidism is an endocrine disorder marked by an abnormal increase in parathormone secretion from one or more parathyroid glands. It is divided into primary and secondary types.
Primary hyperparathyroidism occurs when one or more parathyroid glands produce excessive amounts of parathormone, leading to increased serum calcium concentrations by stimulating bone breakdown and increasing calcium reabsorption in the kidneys. This form is often caused by a benign tumor (adenoma) on a parathyroid gland or, less frequently, by hyperplasia (abnormal cell growth) of all parathyroid glands.
Secondary hyperparathyroidism arises when the parathyroid glands overwork to compensate for low serum calcium levels, often due to vitamin D deficiency or chronic kidney disease.
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What does the parathyroid gland do in the body?
The parathyroid glands, typically four in number in humans, are endocrine glands located near or behind the thyroid. They secrete parathyroid hormone (PTH), which is essential for regulating calcium and phosphate levels in the blood. PTH increases serum calcium concentration by activating bone-dissolving cells, stimulating calcium reabsorption in the kidneys, and promoting calcitriol production for calcium absorption in the gastrointestinal tract.
Hyperparathyroidism involves an abnormal increase in parathormone secretion, leading to elevated serum calcium levels. Primary hyperparathyroidism is often caused by a benign tumor (adenoma) in a parathyroid gland, while secondary hyperparathyroidism occurs as a response to conditions like vitamin D deficiency or chronic kidney disease.
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How does hyperparathyroidism affect the way the parathyroid gland works?
Hyperparathyroidism involves an abnormal increase in parathormone secretion by the parathyroid glands. In primary hyperparathyroidism, one or more parathyroid glands produce excessive parathormone, raising serum calcium levels by breaking down bone and increasing calcium reabsorption in the kidneys. This is often caused by a benign tumor (adenoma) or, less commonly, hyperplasia of all parathyroid glands, leading to parathormone secretion largely independent of serum calcium concentration. Secondary hyperparathyroidism occurs when the parathyroid glands overwork to compensate for low serum calcium, often due to vitamin D deficiency or chronic kidney disease. Parathormone regulates calcium metabolism, and its increased secretion elevates blood calcium levels.
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What are the main symptoms or signs of hyperparathyroidism?
Hyperparathyroidism is an endocrine disorder where one or more parathyroid glands secrete excessive parathormone, leading to elevated serum calcium levels.
Symptoms range from nonspecific to severe. Mild hypercalcemia may present with fatigue, weakness, depression, and appetite loss, or be asymptomatic. Severe hypercalcemia can cause nausea, vomiting, constipation, bone pain, and marked weakness. Kidney stones and osteoporosis may also occur. In rare cases, severe osteoporosis, known as osteitis fibrosa cystica, can develop.
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How does hyperparathyroidism affect the bones and kidneys?
Hyperparathyroidism occurs when there is an abnormal increase in the secretion of parathormone by the parathyroid glands. This can impact the bones and kidneys.
In primary hyperparathyroidism, excessive parathormone stimulates the breakdown of bone and increases calcium reabsorption in the kidneys, which elevates serum calcium concentrations. Over time, bone tissue may be replaced by fibrous tissue, increasing the risk of fractures and skeletal deformities. About 20 percent of cases are detected because patients develop kidney stones.
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What are the common causes of hyperparathyroidism?
Hyperparathyroidism, an elevation in parathormone secretion, has primary and secondary forms. Primary hyperparathyroidism is commonly due to a benign tumor (adenoma) in a parathyroid gland, leading to increased serum calcium. The cause of these parathyroid tumors is often unknown. In about 10% of cases, hyperplasia (increase in cell number) of all parathyroid glands is the cause, which can be related to multiple endocrine neoplasia type 1 (MEN1). Rarely, parathyroid carcinoma is the cause. Secondary hyperparathyroidism occurs when the parathyroid glands overwork to compensate for low serum calcium, often from vitamin D deficiency or chronic kidney disease. Certain drugs, like thiazide diuretics and lithium carbonate, can also cause secondary hyperparathyroidism.
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hyperparathyroidism, abnormal increase in the secretion of parathormone by one or more parathyroid glands.
Hyperparathyroidism may be primary or secondary. In primary hyperparathyroidism, one or more parathyroid glands produces excessive amounts of parathormone. This causes an increase in serum calcium concentrations by stimulating the breakdown of bone and by increasing calcium reabsorption by the kidneys. In secondary (compensatory) hyperparathyroidism, the parathyroid glands become overactive in an attempt to compensate for low serum calcium concentrations. Secondary hyperparathyroidism occurs most often in patients with vitamin D deficiency or chronic kidney disease.
Primary hyperparathyroidism is most often caused by an adenoma (a benign tumour) of one parathyroid gland. The adenoma produces and secretes an excessive amount of parathormone largely independent of the serum calcium concentration. The cause of parathyroid gland tumours is not known. About 10 percent of patients have primary hyperplasia (abnormal increase in the number of cells) of all the parathyroid glands. Primary parathyroid hyperplasia can occur as a result of a familial disorder known as multiple endocrine neoplasia type 1 (MEN1). In rare cases the cause of hyperparathyroidism is attributed to parathyroid carcinoma (a malignant tumour).
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Primary hyperparathyroidism is a relatively common disorder and is usually detected when serum calcium is measured as part of a routine health examination. Most patients have mild hypercalcemia (increased serum calcium concentration), although there are some patients who have no symptoms at all. There are also other patients who have nonspecific symptoms, such as fatigue, weakness, depression, and loss of appetite. Patients with more-severe hypercalcemia may have nausea, vomiting, weight loss, constipation, bone pain, and more-marked weakness and depression. About 20 percent of cases are detected because patients develop kidney stones, and about 1 to 2 percent of cases are detected because the patient has symptomatic osteoporosis (loss of bone). In rare cases, patients have a severe form of osteoporosis called osteitis fibrosa cystica, in which there is intense local resorption of bone that results in the formation of cystlike spaces within the bones that are filled with fibrous tissue.
Secondary hyperparathyroidism may be caused by thiazide diuretic drugs (used to treat hypertension) and lithium carbonate (used to treat depression). In some cases, serum calcium and serum parathormone concentrations are high as a result of a disorder called familial hypocalciuric hypercalcemia (familial benign hypercalcemia). This disorder is caused by a mutation in the calcium receptor gene that reduces the ability of calcium to inhibit parathormone secretion. In most patients with this disorder, serum calcium and parathormone concentrations are only minimally elevated.
Patients with primary hyperparathyroidism with symptoms of hypercalcemia, kidney stones, or bone disease are treated by surgical removal of the tumour (or most of the hyperplastic tissue). The most appropriate treatment of patients with asymptomatic hyperparathyroidism is less clear. Many of these patients remain symptom-free: their serum calcium concentrations do not increase, and their bone density does not decrease. Thus, one alternative is to monitor the patient from year to year, periodically measuring serum calcium and bone density, deciding to treat the patient only when the condition becomes more severe. Another alternative is to treat the patient with a bisphosphonate drug to prevent or decrease the rate of bone loss.
In patients who have acute marked symptoms of hypercalcemia, fluids are administered intravenously as a way to rapidly lower serum calcium concentrations. If that is not effective, a bisphosphonate drug, such as pamidronate or zoledronate, is administered intravenously to reduce hypercalcemia.
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