What is hypoparathyroidism?
Hypoparathyroidism is the term for a low levels of parathyroid hormone (PTH) due to underactivity of the parathyroid gland. Since PTH is an important regulator of calcium and phosphate levels in the body, a deficiency will lead to low calcium and high phosphate levels. This may result in a host of signs and symptoms some of which are similar to an overactive parathyroid gland but with hypoparathyroidism, the bones are left intact and do not weaken and fracture easily. Underactivity of the parathyroid gland is not as common as overactivity of the gland (hyperparathyroidism) and most cases arise with surgical removal, either purposely or accidentally during a thyroidectomy (thyroid gland removal).
Hypoparathyroidism can be classified as primary or secondary hypoparathyroidism, or pseudohypoparathyroidism.
- Primary hypoparathyroidism occurs when there is a deficiency of parathyroid hormone, either due to a parathyroid gland damage or removal.
- Secondary hypoparathyroidism occurs when high levels of calcium in the blood depress PTH secretion although the parathyroid gland is normal.
- Pseudohypoparathyriodism is when the parathyroid gland is functioning normally but the target tissues become resistant to PTH. The circulating levels of PTH are therefore elevated as the gland continues to secrete PTH in an attempt to increase calcium levels.
Causes of Underactive Parathyroid Gland
The causes of hypoparathyroidism can be classified as acquired, inherited or congenital.
- Acquired hypoparathyroidism is not present from birth and is acquired during the course of life.
- Inherited hyperparathyroidism (hereditary) is due to abnormal genes inherited from parents but is not necessarily present from birth.
- Congenital hyperparathyroidism is present from birth and may be due to genetic defects or other conditions during fetal development.
The most common of all the causes is surgically-induced hypoparathyroidism.
- Surgically-induced hypoparathyroidism (iatrogenic hypoparathyroidism) may be purposeful or accidental during the surgical removal of the thyroid gland (thyroidectomy). It may also be mistaken for a lymph node and removed during surgery in certain neck malignancies. Sometimes too much of the parathyroid tissue is removed during surgical treatment of hyperparathyroidism (overactive parathyroid gland) thereby causing a state of hypoparathyroidism.
- Radiation-induced hypoparathyroidism is another form of iatrogenic hypoparathyroidism. This occurs when radiation therapy to the neck, face or upper chest to treat a malignant tumor (cancer) in the area inadvertently damages the parathyroid gland. This type of hypoparathyroidism may also be seen with the use of radioactive iodine used in the treatment of hyperthyroidism (overactive thyroid gland).
- Autoimmune hypoparathyroidism, as the name suggests, is an immune-mediated reaction where the body’s immune system targets the parathyroid gland. APS1 (autoimmune polyendocrine syndrome type 1) is a result of genetic mutation and often associated with chronic mucocutaneous candidiasis and primary adrenal insufficiency.
- Familial isolated hypothyroidism (FIH) may be autosomal-dominant or autosomal-recessive. This means that the autosomal-dominant form requires only one copy of the abnormal gene (from one parent) to cause the condition while the autosomal-recessive form requires two copies of abnormal gene for the disease to develop.
- Congenital hypoparathyroidism is an underactive parathyroid gland that is present from birth. It may be associated with many other conditions. It is also possible that the parathyroid glands are completely absent.
Signs and Symptoms of an Underactive Parathyroid Gland
The persisting low levels of calcium will lead to a host of signs and symptoms, the most prominent of which for hypoparathyroidism, is tetanty. This is intermittent muscle spasms that may be painful and often leads to involuntary twitching of the muscles. It can affect any muscle in the body but tends to occur in the limbs (arms and legs) and lower back.
Tetany is such a key feature of hypoparathyroidism that it may be tested for even when not apparent (latent tetany). It may also be one of the contributing factors for painful menstruation (dysmenorrhea) and headaches which are seen with hypoparathyroidism. If papilledema, nausea and/or vomiting are also present, then the headache may be associated with raised intracranial pressure (pressure on the brain) which may occur with hypoparathyroidism.
Mental symptoms are also quite prominent with an underactive parathyroid gland. This may range from anxiety and nervousness to extreme mood swings and even severe depression. In some cases, patients may be confused, experience hallucinations or display psychotic behavior.
Other features of hypoparathyroidism includes :
- Fatigue and weakness
- Hair loss
- Dry skin
- Brittle nails
- Dental abnormalities
- ECG abnormalities