Parathyroid disease
The body has four parathyroid glands — tiny structures about the size of a grain of rice — located in the neck near the thyroid gland.
Parathyroid glands control your calcium, like a thermostat controls the temperature in your house. If your house is 90 °F, then the thermostat should turn "off" the heater. If the heater is still "on," then your thermostat is broken. Similarly, your parathyroid glands control calcium levels in your blood. If your serum calcium is high, then your parathyroid glands should be "turned off" (i.e., your parathyroid hormone (PTH) should be low). If your serum calcium is high and your parathyroid glands are making lots of PTH, then one or more parathyroid glands are not working correctly. Doctors call this condition primary hyperparathyroidism. Most people with primary hyperparathyroidism have a parathyroid adenoma, which is a benign, enlarged parathyroid gland.
People with kidney problems can have problems with their parathyroid glands also. In these cases all four parathyroid glands grow and calcium levels can be high or low. This is called secondary or tertiary hyperparathyroidism, depending on the calcium levels.