Hypoparathyroidism

Hypoparathyroidism is the combination of symptoms due to inadequate parathyroid hormone production.  This is a very rare condition, and most commonly occurs because of damage to or removal of parathyroid glands at the time of parathyroid or thyroid surgery.   

Hypoparathyroidism is the state of decreased secretion or activity of parathyroid hormone (PTH).  This leads to decreased blood levels of calcium (hypocalcemia) and increased levels of blood phosphorus (hyperphosphatemia). 

Symptoms can range from quite mild (tingling in the hands, fingers, and around the mouth) to more severe forms of muscle cramps leading all the way to tetany (severe muscle cramping of the entire body) and convulsions (this is very rare).

Parathyroid gland insufficiency is quite rare, but it can occur in several well defined ways.  The most common cause of hypoparathyroidism is the loss of active parathyroid tissue following thyroid or parathyroid surgery.  More rare is a defect present at birth (congenital), where a person is born without parathyroid glands.  Occasionally, the specific cause of hypoparathyroidism cannot be determined.

Two Categories of Hypoparathyroidism

• Deficient parathyroid hormone secretion
• Inability of the kidneys and bones to respond to PTH

Deficient Parathyroid Hormone Secretion
This type of hypoparathyroidism is the easiest to understand.  A patient afflicted with this condition simply has too little (or a complete absence of) parathyroid tissue; therefore, inadequate PTH is produced.

There are two major causes of this problem: 

1.  Post-surgical.  The first (and by far most common) cause of inadequate parathyroid hormone production is the removal of parathyroid glands during surgery.  The operations that are typically associated with this problem are operations designed to remove parathyroid glands for hyperparathyroidism.  The goal of this operation is to remove those parathyroid glands that are overproducing PTH. But occasionally, (about 1%-2% of the time) too much parathyroid tissue is removed. 

The second operation associated with post-operative hypoparathyroidism is a total thyroidectomy.   This operation is performed for a number of reasons, but because of the close relationship that the thyroid and parathyroid have to one another (including sharing the same blood supply), the parathyroid glands can be injured or removed.  This is very rare and occurs in less than 1% of thyroid operations.  In many patients, the inadequate secretion of PTH is transient following surgery on the thyroid or parathyroid glands, so this diagnosis cannot be made immediately following surgery.

2. Idiopathic.   Deficient PTH secretion without a defined cause (e.g. surgical injury) is termed Idiopathic hypoparathyroidism.  This disease is rare and can be congenital or acquired later in life.

•  Congenital:   Patients in this category are born without parathyroid tissues.  Most patients with congenital hypoparathyroidism have no family history of the disease. Those who do may have any one of a number of congenital causes.
  
  The pattern of inheritance is as varied as the kinds of genetic abnormalities that cause the disease. The children in some families are at a 50% risk for disease (dominant gene defect), while others are at a risk of 25% or less (recessive gene defect). In some families, only the boys suffer from disease. This sex-linked inheritance pattern indicates the presence of a genetic defect on the X chromosome. The inherited forms tend to arise from abnormal genes that either: 1) encode abnormal forms of PTH or its receptor, 2) prevent normal conduction of cell signals from the PTH receptor to the nucleus, or 3) prevent normal gland development before birth.
  
  Hypoparathyroidism with onset during the first few months of life can be permanent or temporary. The cause is usually unknown if spontaneous resolution occurs.  If it does not, it will usually manifest by 24 months of age. Finally, mothers who have overactive parathyroid glands may have high calcium levels. The excess ionized calcium can enter the baby and suppress the baby’s parathyroid gland function. If suppression of the gland is not released quickly enough after birth, low calcium levels can be a temporary problem for the baby. This will not result in permanent parathyroid gland dysfunction in the child.
• Acquired:   The acquired form of this disease typically arises because the immune system has developed antibodies against parathyroid tissues in an attempt to reject what is sees as a foreign tissue, much as it would a transplanted organ. This disease can affect the parathyroid glands in isolation or can be part of a syndrome that involves many organs.
  
  An antibody that binds to the calcium sensor in the parathyroid gland has been discovered in the blood of patients with autoimmune hypoparathyroidism. It has been proposed that such binding "tricks" the parathyroid gland into believing that the blood level of ionized calcium is high. Responding to this signal, the parathyroid stops making PTH.

3. Hypomagnesemia. The element magnesium is closely related to calcium in the body.  When magnesium levels are too low, calcium levels may also fall.  It appears that magnesium is important for parathyroid cells to make PTH normally.  Once recognized, this is usually very easy to fix.  Chronic alcoholism is a frequent cause of low calcium and magnesium levels.

Resistance to Parathyroid Hormone  (pseudo-hypoparathyroidism)
This disease is also very rare.  Like hypoparathyroidism, this disease is characterized by hypocalcemia (too low calcium levels) and hyperphosphatemia (too high phosphorus levels), but patients with pseudo-hypoparathyroidism (or reistance to PTH) are distinguished by the fact that they produce PTH, but their bones and kidneys do not respond to it.  Even if PTH is given to them in their veins, they do not respond to it.  Therefore, these rare individuals have plenty of PTH, but their organs do not behave appropriately to it. They appear to have hypoparathyroidism,  but they do not; thus the name pseudo-hypoparathyroid.

Treatment of Hypoparathyroidism
Vitamin D and calcium supplements are the primary treatments for hypoparathyroidism, regardless of the cause.  The only exception is when the inactivity of PTH is due to hypomagnesemia, which is readily treated with magnesium supplementation.  At this time, a replacement form of PTH is not available.

• Back to Parathyroid Introduction
• More about Hyperparathyroidism