Prepared by: Daniela Cihakova MD, PhD|
Definition: Autoimmune hypoparathyroidism is an autoimmune inflammatory disease of parathyroid glands, which results in deficiency of the parathormone (PTH).
Description: Four parathyroid glands are placed behind the thyroid. They produce PTH, which is the most important hormone controlling calcium and phosphorus metabolism. If calcium levels in the blood decrease, parathyroid hormone acts in the kidneys and bone and increases serum calcium levels. Parathormone acts through vitamin D in the gastrointestinal tract and enhances absorption of calcium. Hyposecretion of PTH causes depressed serum calcium levels, and increased phosphate serum levels.
Symptoms: Hypocalcemia can manifest only during fasting or low calcium intake in the beginning when only reserve secretory capacity of parathyroid gland is lost. Symptoms include:
Tetany can lead to laryngospasm and seizures and can be life threatening.
- neuromusclar irritability,
- numbness or burning/tickling/tingling (paresthesia) of hands or feet,
- and psychosis.
In differential diagnosis, it is important to distinguish idiopathic hypoparathyreosis from DiGeorge syndrome and pseudohypoparathyroidism. Also, patients with idiopathic hypoparathyroidism should always be repeatedly screened for Addison’s disease, because hypoparathyreodism can be the first sign of polyglandular autoimmune disease type 1 (see there).
- Blood tests: low calcium level, elevated phosphorus level, decrease parathyroid hormone level, and (sometimes) decreased magnesium level.
- Clinical signs:
- Trousseau sign: hand spasm occurs when an inflate blood pressure cuff is left around arm for several minutes.
- Chvostek sign: tapping on the facial nerve in front of the ear causes contraction of muscles of eye, mouth, and nose
- EKG: prolonged QT interval
Incidence: Not known in the U.S.
In Japan, it is 7.2 per million people. Idiopathic hypoparathyroidism is usually sporadic, but it may occur on a familial basis. The age of onset is usually the first decade of life.
Treatment: Oral calcium carbonate and vitamin D. A high-calcium, low-phosphorous diet is recommended.. Parathyroid hormone cannot be used in treatment. Regular blood calcium levels monitoring is very important.
Pathogenesis: It is believed that idiopathic hypoparathyroidism is an autoimmune disease; however, there is only a limited evidence to support it, given that the disease is very rare. The evidence is circumstantial and consists of the following:
Hypoparathyroidism is very often a part of PAS-1 (see there)
- Patients with hypoparathyreosis have antibodies against parathyroid cells and calcium-sensing receptor in parathyroid gland.