Secondary hyperparathyroidism
Encyclopedia
Secondary hyperparathyroidism refers to the excessive secretion of parathyroid hormone
(PTH) by the parathyroid gland
s in response to hypocalcemia (low blood
calcium
levels) and associated hypertrophy of the glands. This disorder is especially seen in patients with chronic renal failure. It is often—although not consistently—abbreviated as SHPT in medical literature.
is the most common cause of secondary hyperparathyroidism. Failing kidneys do not convert enough vitamin D
to its active form, and they do not adequately excrete phosphate
. When this happens, insoluble calcium phosphate
forms in the body and removes calcium from the circulation. Both processes lead to hypocalcemia and hence secondary hyperparathyroidism. Secondary hyperparathyroidism can also result from malabsorption (chronic pancreatitis, small bowel disease, malabsorption-dependent bariatric surgery
) in that the fat soluble vitamin D can not get reabsorbed. This leads to hypocalcemia and a subsequent increase in parathyroid hormone secretion in an attempt to increase the serum calcium levels.
such as calcitriol
, Hectorol, Zemplar(paricalcitol), etc. and phosphate binders
which can be divided into calcium-based and non-calcium based. A newer class of medications is calcimimetics, one of which is commercially available as Sensipar (cinacalcet
) in the US and Australia, and as Mimpara in the EU. Calcimimetics have achieved positive responses and are FDA approved for use in patients on dialysis, but have not been approved for use in chronic kidney disease pre-dialysis because, among other concerns, they can increase phosphorus levels. Most patients with hyperparathyroidism secondary to chronic kidney disease will improve after renal transplantation, but many will continue to have a degree of residual hyperparathyroidism (tertiary hyperparathyroidism) post-transplant with associated risk of bone loss, etc.
, where correction of the underlying cause will not stop excess PTH secretion, i.e. parathyroid gland hypertrophy becomes irreversible.
Parathyroid hormone
Parathyroid hormone , parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands as a polypeptide containing 84 amino acids...
(PTH) by the parathyroid gland
Parathyroid gland
The parathyroid glands are small endocrine glands in the neck that produce parathyroid hormone. Humans usually have four parathyroid glands, which are usually located on the rear surface of the thyroid gland, or, in rare cases, within the thyroid gland itself or in the chest...
s in response to hypocalcemia (low blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
levels) and associated hypertrophy of the glands. This disorder is especially seen in patients with chronic renal failure. It is often—although not consistently—abbreviated as SHPT in medical literature.
Signs and Symptoms
Bone and joint pain are common, as are limb deformities. The elevated PTH has also pleiotropic effects on blood, immune system and neurological system.Diagnosis
The PTH is elevated due to decreased levels of calcium or 1,25-dihydroxy-vitamin D3. It is usually seen in cases of chronic renal disease or defective calcium receptors on the surface of parathyroid glands.Etiology
Chronic renal failureChronic renal failure
Chronic kidney disease , also known as chronic renal disease, is a progressive loss in renal function over a period of months or years. The symptoms of worsening kidney function are unspecific, and might include feeling generally unwell and experiencing a reduced appetite...
is the most common cause of secondary hyperparathyroidism. Failing kidneys do not convert enough vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
to its active form, and they do not adequately excrete phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
. When this happens, insoluble calcium phosphate
Calcium phosphate
Calcium phosphate is the name given to a family of minerals containing calcium ions together with orthophosphates , metaphosphates or pyrophosphates and occasionally hydrogen or hydroxide ions ....
forms in the body and removes calcium from the circulation. Both processes lead to hypocalcemia and hence secondary hyperparathyroidism. Secondary hyperparathyroidism can also result from malabsorption (chronic pancreatitis, small bowel disease, malabsorption-dependent bariatric surgery
Bariatric surgery
Bariatric surgery includes a variety of procedures performed on people who are obese. Weight loss is achieved by reducing the size of the stomach with an implanted medical device or through removal of a portion of the stomach or by resecting and re-routing the small intestines...
) in that the fat soluble vitamin D can not get reabsorbed. This leads to hypocalcemia and a subsequent increase in parathyroid hormone secretion in an attempt to increase the serum calcium levels.
Treatment
If the underlying cause of the hypocalcemia can be addressed, the hyperparathyroidism will resolve. In patients with chronic renal failure, treatment consists of dietary restriction of phosphorus, supplements with an active form of vitamin DVitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
such as calcitriol
Calcitriol
Calcitriol , also called 1,25-dihydroxycholecalciferol or 1,25-dihydroxyvitamin D3, is the hormonally active form of vitamin D with three hydroxyl groups...
, Hectorol, Zemplar(paricalcitol), etc. and phosphate binders
Phosphate binders
Phosphate binders are a group of medications used to reduce the absorption of phosphate and taken with meals and snacks. They are typically used in patients with chronic renal failure as they cannot get rid of the phosphates that get into their blood Phosphate binders are a group of medications...
which can be divided into calcium-based and non-calcium based. A newer class of medications is calcimimetics, one of which is commercially available as Sensipar (cinacalcet
Cinacalcet
Cinacalcet is a drug that acts as a calcimimetic by allosteric activation of the calcium-sensing receptor that is expressed in various human organ tissues. It is sold by Amgen under the trade name Sensipar in North America and Australia and as Mimpara in Europe...
) in the US and Australia, and as Mimpara in the EU. Calcimimetics have achieved positive responses and are FDA approved for use in patients on dialysis, but have not been approved for use in chronic kidney disease pre-dialysis because, among other concerns, they can increase phosphorus levels. Most patients with hyperparathyroidism secondary to chronic kidney disease will improve after renal transplantation, but many will continue to have a degree of residual hyperparathyroidism (tertiary hyperparathyroidism) post-transplant with associated risk of bone loss, etc.
Prognosis
If left untreated, the disease will progress to tertiary hyperparathyroidismTertiary hyperparathyroidism
Tertiary hyperparathyroidism is a state of excessive secretion of parathyroid hormone after a long period of secondary hyperparathyroidism and resulting hypercalcemia...
, where correction of the underlying cause will not stop excess PTH secretion, i.e. parathyroid gland hypertrophy becomes irreversible.