Abstract

Hypoparathyroidism results in a disruption of calcium and phosphorus homeostasis, leading to a range of clinical manifestations, including neuromuscular symptoms, cardiac abnormalities, and bone abnormalities. Management typically involves supplementation with calcium and active vitamin D analogs to maintain adequate calcium levels and minimize symptoms associated with hypocalcemia

What happens when too little parathyroid hormone is secreted?

When too little parathyroid hormone (PTH) is secreted, a condition known as hypoparathyroidism occurs. Hypoparathyroidism is characterized by insufficient PTH levels, leading to disturbances in calcium and phosphorus metabolism. Here’s what happens when PTH secretion is inadequate:

1. Hypocalcemia: One of the primary consequences of hypoparathyroidism is low blood calcium levels (hypocalcemia). PTH normally acts to increase calcium levels in the blood by stimulating the release of calcium from bones, enhancing renal calcium reabsorption, and promoting the production of active vitamin D (calcitriol), which enhances intestinal calcium absorption. In hypoparathyroidism, the absence or deficiency of PTH leads to reduced calcium mobilization from bones, decreased renal calcium reabsorption, and impaired intestinal calcium absorption, resulting in hypocalcemia.
2. Neuromuscular Symptoms: Hypocalcemia can manifest with various neuromuscular symptoms due to the essential role of calcium ions in nerve and muscle function. Symptoms may include muscle cramps, spasms, twitching, numbness or tingling (paresthesias), and seizures. Severe hypocalcemia can lead to tetany, a condition characterized by involuntary muscle contractions, particularly affecting the hands and feet.
3. Cardiac Arrhythmias: Low calcium levels can also affect cardiac function, potentially leading to cardiac arrhythmias (irregular heart rhythms) such as prolongation of the QT interval on electrocardiogram (ECG). Severe hypocalcemia may predispose individuals to life-threatening arrhythmias, including ventricular tachycardia and ventricular fibrillation.
4. Bone Abnormalities: Chronic hypocalcemia resulting from prolonged hypoparathyroidism can lead to alterations in bone metabolism and mineralization. Reduced calcium levels in the extracellular fluid can impair bone mineralization, potentially leading to osteopenia (reduced bone density) or osteomalacia (softening of bones).
5. Increased Phosphorus Levels: In addition to hypocalcemia, hypoparathyroidism can also lead to elevated blood phosphorus levels (hyperphosphatemia). Normally, PTH inhibits renal tubular reabsorption of phosphorus, leading to phosphaturia (excretion of phosphorus in urine). In hypoparathyroidism, the absence of PTH results in reduced renal phosphorus excretion, contributing to hyperphosphatemia.

In hypoparathyroidism, several laboratory tests may show abnormalities indicative of impaired calcium and phosphorus metabolism. Here are the typical findings in primary hypoparathyroidism and the life-threatening complications associated with the condition:

1. Abnormal Laboratory Findings in Hypoparathyroidism:
   • Hypocalcemia: Serum calcium levels are typically low due to decreased calcium mobilization from bones, impaired renal calcium reabsorption, and decreased intestinal calcium absorption.
   • Hyperphosphatemia: Blood phosphorus levels may be elevated as a result of reduced renal phosphorus excretion due to insufficient parathyroid hormone (PTH) action.
   • Low or Inappropriately Normal PTH Levels: In primary hypoparathyroidism, PTH levels are usually low or inappropriately normal despite hypocalcemia. This is because the parathyroid glands fail to produce or secrete adequate amounts of PTH.
2. Blood Results for Primary Hypoparathyroidism:
   • Serum Calcium: Low (hypocalcemia)
   • Serum Phosphorus: High (hyperphosphatemia)
   • Serum Parathyroid Hormone (PTH): Low or inappropriately normal
3. Life-Threatening Complications of Hypoparathyroidism:
   • Tetany: Severe hypocalcemia can lead to tetany, a condition characterized by involuntary muscle spasms and contractions. Tetany can manifest as carpopedal spasms (involuntary flexion of the wrists and fingers), laryngospasm (spasm of the vocal cords leading to difficulty breathing), and seizures. Severe tetany can be life-threatening if not promptly treated with intravenous calcium.
   • Cardiac Arrhythmias: Profound hypocalcemia can affect cardiac function, leading to cardiac arrhythmias such as ventricular tachycardia or torsades de pointes. These arrhythmias can cause hemodynamic instability and cardiac arrest if left untreated.
   • Chvostek’s Sign and Trousseau’s Sign: These are clinical manifestations of neuromuscular irritability seen in hypocalcemia. Chvostek’s sign refers to facial muscle twitching elicited by tapping the facial nerve, while Trousseau’s sign is the induction of carpal spasm by inflating a blood pressure cuff above systolic pressure for a few minutes. These signs indicate severe hypocalcemia and can precede the onset of tetany.

Hypoparathyroidism can lead to life-threatening complications, particularly when severe hypocalcemia is present. Prompt recognition and treatment of hypocalcemia are essential to prevent complications and ensure patient safety. Treatment typically involves calcium and vitamin D supplementation to maintain normal serum calcium levels and alleviate symptoms associated with hypocalcemia

Verified by: Dr.Diab (March 29, 2024)

Citation: Dr.Diab. (March 29, 2024). What happens when too little parathyroid hormone is secreted?. Medcoi Journal of Medicine, 3(2). urn:medcoi:article32912.