Hyperparathyroidism comes in three different forms, but essential all result in an increase in the level of parathyroid hormone. Before being able to understand the different types of hyperparathyroidism, we first need to understand the role of the parathyroid hormone (PTH).
PTH is produced in the parathyroid glands. We have 4 of these glands which sit in our thyroid gland, an “H” shaped gland in our necks. PTH is secreted from these glands in a response to a low level of calcium within the blood. PTH then causes:
1- Calcium to be released from the bone by stimulating osteoclasts to break down bone.
2- Stimulates the kidneys to increase the reabsorption of calcium, so less calcium is lost in the urine
3- Activation of a hormone in the kidneys that are involved in the conversion of inactive vitamin D to active vitamin D. Increased levels of active vitamin D then act on the intestines to increase the absorption of calcium
All of these lead to an increase in free calcium within the blood. Calcium levels in the blood are important as they are involved in a number of processes; such as blood clotting, hormone secretion, contraction of the muscle and generating action potentials within neurons.
So back to hyperparathyroidism. The three types are classified as primary, secondary and tertiary. Primary hyperparathyroidism is the inappropriate secretion of PTH from the parathyroid glands that are not due to external stimulation, most commonly due to a parathyroid gland adenoma. The secondary is therefore when an external stimulus triggers excess secreting of PTH, for example, a hypocalcaemia picture caused by chronic kidney disease. Tertiary hyperparathyroidism is slightly different in the fact that it is an excessive secretion of PTH however is a result of secondary where the parathyroid gland becomes desensitised to external stimulation.
High levels of calcium can lead to kidney stones and less neuronal stimulation (harder to produce action potentials). Whereas due to the calcium being released from bones in this process, bone pain can be a symptom as well as an increased risk of fractures due to bone fragility.