What are the Parathyroid Glands?
The parathyroid glands are four small glands that reside in the neck adjacent to the thyroid gland. They play an integral role in blood stream calcium level monitoring and regulation.
Approximately 1-2% of the total body calcium exists in the blood stream, while 98% is contained within the bones. Although the blood stream calcium accounts for a very small percentage of total body calcium, its regulation is critical for normal muscle, nerve and heart function.
The parathyroid glands monitor serum calcium levels and produce parathyroid hormone (PTH) in response to decreasing levels. Parathyroid hormone acts at the level of the bone to cause the release of calcium into the bloodstream. As the bloodstream calcium levels rise, the parathyroid glands recognize this increase and diminish the production of parathyroid hormone. This results in what is called a negative feedback loop.
Bloodstream calcium levels are also affected by vitamin D which functions to allow calcium absorption in the digestive tract. Vitamin D is consumed in the diet and is activated through a multistep process that requires UV light exposure. Vitamin D, when activated, facilitates the absorption of calcium into the bloodstream. The final step of vitamin D activation occurs in the kidneys and can be affected when kidney function is abnormal.
Hyperparathyroidism is a term that describes over function of one or more of the parathyroid glands. Primary hyperparathyroidism is the most common form and results from the loss of the normal response by the parathyroid glands to rising calcium levels. As a result, primary hyperthyroidism is manifested by elevated blood calcium levels while PTH levels are also elevated. Primary hyperparathyroidism most commonly results from a parathyroid adenoma (benign enlargement of the gland) involving one of the 4 glands.
Single gland involvement accounts for nearly 80% of the cases of primary hyperparathyroidism. 15% of the time, all 4 glands are slightly enlarged and over functioning; while the remainder of cases involve 2 or 3 glands. Primary hyperparathyroidism can present with symptoms such as kidney stones, stomach ulcers, bone fractures, or anxiety and depression.
These days, it is commonly diagnosed by the identification of an elevated calcium level on routine blood work. Many patients are candidates for surgical treatment prior to the development of symptoms that are associated with advanced disease.
Secondary hyperparathyroidism is a condition that occurs when blood calcium levels are low causing chronic stimulation of the parathyroid glands to produce parathyroid hormone. This is most commonly seen in kidney failure as a result of the inability to convert vitamin D to its active form.
The parathyroid glands maintain the ability to respond normally to the calcium level, but they are unable to correct the low calcium. This results in enlargement of all 4 parathyroid glands. Secondary hyperparathyroidism will present with diffuse bone pain and bone mineral loss. Secondary hyperparathyroidism is often controlled with medications.
Tertiary hyperparathyroidism results when the glands of secondary hyperparathyroidism lose their ability to respond appropriately to calcium levels. This is most commonly seen after kidney transplantation with the improvement of vitamin D levels associated with the rise in calcium levels. Tertiary hyperparathyroidism will present with elevated calcium levels as well as elevated PTH levels. This is most commonly manifested by all 4 glands.
Parathyroid surgery has evolved over the past 2 decades. Hyperparathyroidism traditionally was treated by neck exploration allowing the surgeon to visualize all 4 parathyroid glands. As imaging and lab monitoring have improved, minimally invasive parathyroid surgery has become the standard of care. If a parathyroid gland can be demonstrated as enlarged by either ultrasound or nuclear medicine scanning (Sestimibi scanning), the surgeon can approach this single gland without having to disturb the rest of the neck. This allows for a more cosmetically pleasing scar as well as the possibility of same day discharge from the hospital. Intraoperative PTH monitoring has also allowed the surgeon to demonstrate cure of the disease while in the operating room and decreases the likelihood of leaving additional hyperfunctioning parathyroid tissue. Hyperparathyroidism is only cured through surgical intervention. In experienced hands, parathyroid surgery is successful 97-98% of the time.
Parathyroid imaging can be achieved using ultrasound or Sestimibi scanning. Ultrasound can be performed by the surgeon and is relatively inexpensive. This allows the surgeon to have a more detailed understanding of the location of the parathyroid gland and the surrounding anatomy. Additional imaging may involve CT scan or MRI scanning.