Normocalcemic Primary Hyperparathyroidism

Easy reading

Patients with an elevated parathyroid hormone (PTH) level and normal calcium levels can have one of two problems. Most often, the parathyroid glands are responding to a different problem elsewhere in the body. Problems with low vitamin D levels, not taking in enough calcium in the diet or putting out too much calcium in the urine are common examples of problems that can cause the parathyroid glands to work too hard. Patients who have had gastric bypass surgery for weight loss can have this problem, too. PTH levels can become normal again by fixing the problem elsewhere in the body. The parathyroid glands are doing their job the way it is supposed to be done.

Another type of problem where the calcium is normal and the PTH level is higher than normal is called normocalcemic primary hyperparathyroidism. Normocalcemic means the calcium level measured in the blood is in the normal range. This may be the very beginning of a problem with the parathyroid glands. With this type of problem, the parathyroid glands are not responding correctly to the signals the body is giving them. Sometimes, the type of calcium measured in the blood is falsely low, and another type of calcium (ionized calcium) is a better type of calcium to check to see if it is elevated. If the ionized calcium level is high and the PTH level is high, this is the same as primary hyperparathyoidism and is not ‘normocalcemic’.

During this time, even though the calcium level is normal, because the PTH level is high, patients can still develop weak bones and kidney stones. Over time, in patients with normocalcemic primary hyperparathyroism, the calcium level may become higher than normal. This is called primary hyperparathyroidism. This rise in calcium from normal to higher than normal when PTH levels are high happens in 1 out of 5 patients when followed for over 4 years. During this time, even though the calcium level is normal, because the PTH level is high, patients can still develop weak bones and kidney stones.   

It isn’t clear if patients with normocalcemic primary hyperparathyroidism should undergo surgery. It depends on what other problems patients have. Every patient should be given the chance to meet with an expert parathyroid surgeon to help decide if surgery would be helpful in this situation.

In-depth reading

Patients with an elevated parathyroid hormone and normal calcium levels require special consideration.  Causes of secondary hyperparathyroidism (vitamin D deficiency, renal calcium loss and malabsorption) should be considered and ruled out.  In some patients the total serum calcium (albumin corrected) may be normal while the ionized calcium is elevated.  After appropriate investigation these patients may be determined to have normocalcemic hyperparathyroidism.  Many consider it to be an early form of traditional primary hyperparathyroidism.  Despite normal calcium levels these patients may develop reduced bone mineral density or kidney stones.  When followed non-operatively about 20% of these patients over 4 years will progress to a biochemical picture consistent with traditional primary hyperparathyroidism.   

The issue of surgery in normocalcemic hyperparathyroidism is unclear. Following surgery, biochemical indices tend to return to normal.  However the long-term benefits of surgery in this sub-group are as of yet not clearly defined.  Perhaps some patients can be followed long term without significant adverse effects and surgery could be offered to a subset of patients with specific clinical indicators.  This issue should be clarified with further study.  Currently it is prudent to have patients with normocalcemic hyperparathyroidism meet with an experienced parathyroid surgeon to discuss the options and potential risks and benefits of surgery.  Decision should be made on a case by case basis.