Primary Hyperparapthrydoidism (1˚HPT)

Primary Hyperparpathyroidism

This is a parathyroid adenoma. It is a benign growth of one of the parathyroid glands and is the most common cause of 1°HPT. This gland weighs about 500 mg (about 10× normal size) and it is a typical parathyroid adenoma. One can appreciate how it is different from the normal parathyroid gland seen on the previous page.

1°HPT is an elevated PTH level cased by a primary problem with the parathyroid gland itself. That is to say, an overgrowth of abnormally functioning parathyroid cells causes too much PTH to be produced. This happens because the calcium sensing receptors are reduced and calcium particles can’t turn off the parathyroid glands. Therefore the glands are always” turned on” and constantly produce too much PTH leading to the health problems we discussed earlier. Genetic abnormalities in the parathyroid cells cause a decrease in these receptors and a overgrowth of abnormally functioning cells. If this happens to only one gland it is an adenoma. If all the glands are overgrown it is called hyperplasia. These are benign conditions. While we understand a lot about how this happens, we really don’t know why it happens or the specific cause in a given patient. It occurs more often in people who have had head and neck radiation( not simple x-rays or CT scans). It can be inherited. It is more common in women than men, especially post-menopausal women.

1°HPT is commonly found through routine screening blood work that shows an elevated calcium level. Not uncommonly, this elevated calcium may be thought to be a lab error or an irrelevant finding but most often it represents a significant issue. Sometimes patients may present with a kidney stone or osteoporosis and a fracture after relatively minor trauma.

When an elevated calcium is found it should be evaluated. There are many causes of elevated calcium but part of the work-up includes checking a PTH level. If both the PTH and calcium are elevated then 1°HPT is likely. This feature of 1°HPT readily separates it from other causes of hypercalcemia.  If the PTH level is in the low normal range then other causes of elevated calcium should be investigated.

A vitamin D level is frequently checked during an evaluation for hypercalcemia. In-directly 1°HPT results in a modest decrease in vitamin D. This may be confusing to patients and some physicians. Mistakenly, It may be assumed that low vitamin D seen with 1°HPT is the cause of the hypercalcemia when in fact it is the result of hyperparathyroidism. Vitamin D supplements in this setting will not correct low vitamin D level or the abnormal calcium physiology. Low vitamin D levels may be associated with elevated PTH levels but the calcium level will be low.

Once 1°HPT is suspected, 3 fasting calcium levels and at least 2 PTH levels, a week apart, should be checked. Kidney function should be confirmed to be normal and thiazide diuretics stopped if possible as this may lead to confusing lab results. Vitamin D levels should also be evaluated. Rarely, 1°HPT can be confused with an inherited syndrome called Benign Familial Hypocalciuric Hypercalcemia (FHH). A review of family history, checking the magnesium level and urine for calcium excretion usually excludes this rare disorder. In 1°HPT the magnesium level is low and calcium in the urine is usually elevated. In FHH the magnesium level is usually elevated and urine calcium excretion is low.

Age many affect the normal range for calcium and PTH. The calcium level really should not be greater than 10 in patients over 50 years old. PTH levels in these patients should not be higher than 50. Therefore, in patients over 50, high normal calcium levels and high normal PTH levels may represent 1°HPT. Additionally in patients with elevated calcium levels the PTH  level should be low if the parathyroid glands are functioning normally. Therefore, patients with high calcium levels and high normal PTH levels (non-suppressed PTH) commonly have 1°HPT.

Generally, a single adenoma is responsible for about 80% of 1°HPT. About 13% of patients have hyperplasia, where all the glands are enlarged and overactive. About 7% of patients have hyperparathyroidism due to double adenomas (2 glands are enlarged, usually the superior glands). Less than 1% of patients with 1°HPT have parathyroid cancer.

Click on the following links for more information: treatment of 1°HPT, risk of surgery,post-op care.