In hyperparathyroidism, one or more of the tiny parathyroid glands in the neck are over-producing parathyroid hormone. The excess amount of this hormone in the blood causes hypercalcemia, which is an abnormally high level of calcium. Symptoms of this condition include bone and joint pain, weakened bones, abdominal pain and other issues, though many times these symptoms are fairly mild. Primary hyperparathyroidism is when one or more parathyroid glands become enlarged (sometimes due to a tumor) and start producing too much hormone, while secondary hyperparathyroidism is when an underlying disease is present that causes an abnormally low level of calcium, which in turn stimulates the parathyroids to produce more hormones. Treatment of hyperparathyroidism may entail close monitoring of blood calcium, kidney function and bone density; surgery to remove malfunctioning parathyroid glands; various medications; and hormone replacement therapy.